fix(assembly): update solver submodule — enforce drag quaternion continuity (#338)

Points solver to fix/drag-quat-continuity (solver#40) which fixes
the planar constraint drift during interactive drag by enforcing
quaternion continuity on dragged parts and detecting branch jumps
beyond simple hemisphere negation.

.gitea/workflows/release.yml

@@ -322,6 +322,7 @@ jobs:
 
     env:
       BUILD_TAG: ${{ github.ref_name || inputs.tag }}
+      COMMIT_SHA: ${{ github.sha }}
       NODE_EXTRA_CA_CERTS: /etc/ssl/certs/ca-certificates.crt
 
     steps:
@@ -386,6 +387,7 @@ jobs:
               'name': f'Kindred Create {tag}',
               'body': body,
               'prerelease': prerelease,
+              'target_commitish': '${COMMIT_SHA}',
           }))
           ")
 

.gitignore

@@ -77,3 +77,5 @@ docs/book/
 
 # To regenerate themed icons: python3 icons/retheme.py
 # icons/themed/ is tracked (committed) so CI builds include them
+
+CLAUDE.md

.gitmodules

@@ -22,3 +22,6 @@
 	path = mods/solver
 	url = https://git.kindred-systems.com/kindred/solver.git
 	branch = main
+[submodule "mods/quicknav"]
+	path = mods/quicknav
+	url = https://git.kindred-systems.com/kindred/quicknav.git

CLAUDE.md

@@ -0,0 +1,285 @@
+# CLAUDE.md — Developer Context for Kindred Create
+
+## Project Overview
+
+Kindred Create is a fork of FreeCAD 1.0+ that adds integrated tooling for professional engineering workflows. It ships a context-aware UI system, two addon command sets (ztools and Silo), a Catppuccin Mocha dark theme, and a pluggable file origin layer on top of FreeCAD's parametric modeling core.
+
+- **Kindred Create version:** 0.1.5
+- **FreeCAD base version:** 1.2.0
+- **License:** LGPL-2.1-or-later
+- **Repository:** `git.kindred-systems.com/kindred/create` (Gitea)
+- **Main branch:** `main`
+
+## Quick Start
+
+```bash
+git clone --recursive ssh://git@git.kindred-systems.com:2222/kindred/create.git
+cd create
+pixi run configure      # CMake configure (debug by default)
+pixi run build          # Build
+pixi run install        # Install to build dir
+pixi run freecad        # Launch
+pixi run test           # Run C++ tests (ctest)
+pixi run test-kindred   # Run Python/Kindred tests
+```
+
+Build variants: append `-debug` or `-release` (e.g., `pixi run build-release`). See `CMakePresets.json` for platform-specific presets (Linux x86_64/aarch64, macOS Intel/ARM, Windows x64).
+
+## Repository Structure
+
+```
+create/
+├── src/
+│   ├── App/                    Core application (C++)
+│   ├── Base/                   Base classes, type system, persistence (C++)
+│   ├── Gui/                    GUI framework (C++)
+│   │   ├── EditingContext.h    Editing context resolver (Kindred feature)
+│   │   ├── BreadcrumbToolBar.h Breadcrumb navigation widget (Kindred feature)
+│   │   ├── FileOrigin.h        Abstract origin interface (Kindred feature)
+│   │   ├── OriginManager.h     Origin lifecycle management
+│   │   ├── CommandOrigin.cpp   Origin_Commit/Pull/Push/Info/BOM commands
+│   │   ├── ApplicationPy.h     All FreeCADGui.* Python bindings
+│   │   ├── Application.h       App signals (fastsignals)
+│   │   ├── Stylesheets/        QSS theme files
+│   │   └── PreferencePacks/    Preference configurations (build-time generated)
+│   ├── Mod/                    FreeCAD modules (PartDesign, Assembly, Sketcher, etc.)
+│   │   └── Create/            Kindred Create module
+│   │       ├── Init.py         Console bootstrap — loads addons
+│   │       ├── InitGui.py      GUI bootstrap — loads addons, Silo setup, update checker
+│   │       ├── addon_loader.py Manifest-driven loader with dependency resolution
+│   │       └── kc_format.py    .kc file format preservation
+│   └── 3rdParty/              Vendored dependencies
+│       ├── OndselSolver/      [submodule] Assembly constraint solver (forked)
+│       ├── FastSignals/       Signal/slot library (NOT Boost)
+│       └── GSL/               [submodule] Microsoft Guidelines Support Library
+├── mods/                       Kindred addon modules
+│   ├── sdk/                   Addon SDK — stable API contract (priority 0)
+│   ├── ztools/                [submodule] Command provider (priority 50)
+│   ├── silo/                  [submodule] PLM workbench (priority 60)
+│   ├── solver/                [submodule] Assembly solver research (GNN-based)
+│   └── quicknav/              [submodule] Navigation addon
+├── docs/                       mdBook documentation + architecture docs
+├── tests/                      C++ unit tests (GoogleTest)
+├── package/                    Packaging (debian/, rattler-build/)
+├── resources/                  Branding, icons, desktop integration
+├── cMake/                      CMake helper modules
+├── .gitea/workflows/           CI/CD pipelines
+├── CMakeLists.txt              Root build configuration (CMake 3.22.0+)
+├── CMakePresets.json           Platform build presets
+└── pixi.toml                  Pixi environment and build tasks
+```
+
+## Build System
+
+- **Primary:** CMake 3.22.0+ with Ninja generator
+- **Environment:** [Pixi](https://pixi.sh) (conda-forge) manages all dependencies
+- **Key deps:** Qt 6.8.x, Python 3.11.x, OpenCASCADE 7.8.x, PySide6, Boost, VTK, SMESH
+- **Presets:** `conda-linux-debug`, `conda-linux-release`, `conda-macos-debug`, `conda-macos-release`, `conda-windows-debug`, `conda-windows-release`
+- **Tasks summary:**
+
+| Task | Description |
+|------|-------------|
+| `pixi run configure` | CMake configure (debug) |
+| `pixi run build` | Build (debug) |
+| `pixi run install` | Install to build dir |
+| `pixi run freecad` | Launch FreeCAD |
+| `pixi run test` | C++ tests via ctest |
+| `pixi run test-kindred` | Python/Kindred test suite |
+
+## Architecture Patterns
+
+### Signals — Use FastSignals, NOT Boost
+
+```cpp
+#include <fastsignals/signal.h>
+// See src/Gui/Application.h:121-155 for signal declarations
+```
+
+All signals in `src/Gui/` use `fastsignals::signal`. Never use Boost.Signals2.
+
+### Type Checking Across Modules
+
+Avoid header dependencies between `src/Gui/` and `src/Mod/` by using runtime type checks:
+
+```cpp
+auto type = Base::Type::fromName("Sketcher::SketchObject");
+if (obj->isDerivedFrom(type)) { ... }
+```
+
+### Python Bindings
+
+All `FreeCADGui.*` functions go in `src/Gui/ApplicationPy.h` and `src/Gui/ApplicationPy.cpp`. Use `METH_VARARGS` only (no `METH_KEYWORDS` in this file). Do not create separate files for new Python bindings.
+
+### Toolbar Visibility
+
+Use `ToolBarItem::DefaultVisibility::Unavailable` to hide toolbars by default, then `ToolBarManager::setState(ForceAvailable)` to show them contextually. This pattern is proven by the Sketcher module.
+
+The `appendToolbar` Python API accepts an optional 3rd argument: `"Visible"`, `"Hidden"`, or `"Unavailable"`.
+
+### Editing Context System
+
+The `EditingContextResolver` singleton (`src/Gui/EditingContext.h/.cpp`) drives the context-aware UI. It evaluates registered context definitions in priority order and activates the matching one, setting toolbar visibility and updating the `BreadcrumbToolBar`.
+
+Built-in contexts: `sketcher.edit`, `assembly.edit`, `partdesign.feature`, `partdesign.body`, `assembly.idle`, `spreadsheet`, `empty_document`, `no_document`.
+
+Python API:
+- `FreeCADGui.registerEditingContext()` — register a new context
+- `FreeCADGui.registerEditingOverlay()` — conditional toolbar overlay
+- `FreeCADGui.injectEditingCommands()` — add commands to existing contexts
+- `FreeCADGui.currentEditingContext()` — query active context
+- `FreeCADGui.refreshEditingContext()` — force re-evaluation
+
+### Addon Loading
+
+Addons in `mods/` are loaded by `src/Mod/Create/addon_loader.py`. Each addon provides a `package.xml` with `<kindred>` extensions declaring version bounds, load priority, and dependencies. The loader resolves via topological sort: **sdk** (0) -> **ztools** (50) -> **silo** (60).
+
+A `<workbench>` tag in `package.xml` is required for `InitGui.py` to be loaded, even if no actual workbench is registered.
+
+### Deferred Initialization
+
+GUI setup uses `QTimer.singleShot` with staggered delays:
+- 500ms: `.kc` file format registration
+- 1500ms: Silo origin registration
+- 2000ms: Auth dock + ztools commands
+- 2500ms: Silo overlay
+- 3000ms: Silo first-start check
+- 4000ms: Activity panel
+- 10000ms: Update checker
+
+### Unified Origin System
+
+File operations (New, Open, Save, Commit, Pull, Push) are abstracted behind `FileOrigin` (`src/Gui/FileOrigin.h`). `LocalFileOrigin` handles local files; `SiloOrigin` (`mods/silo/freecad/silo_origin.py`) backs Silo-tracked documents. The active origin is selected automatically based on document properties (`SiloItemId`, `SiloPartNumber`).
+
+## Submodules
+
+| Path | Repository | Branch | Purpose |
+|------|------------|--------|---------|
+| `mods/ztools` | `git.kindred-systems.com/forbes/ztools` | `main` | Extended PartDesign/Assembly/Spreadsheet tools |
+| `mods/silo` | `git.kindred-systems.com/kindred/silo-mod` | `main` | PLM workbench (includes silo-client submodule) |
+| `mods/solver` | `git.kindred-systems.com/kindred/solver` | `main` | Assembly solver research (GNN-based) |
+| `mods/quicknav` | `git.kindred-systems.com/kindred/quicknav` | — | Navigation addon |
+| `src/3rdParty/OndselSolver` | `git.kindred-systems.com/kindred/solver` | — | Constraint solver (forked with NR fix) |
+| `src/3rdParty/GSL` | `github.com/microsoft/GSL` | — | Guidelines Support Library |
+| `src/Mod/AddonManager` | `github.com/FreeCAD/AddonManager` | — | FreeCAD addon manager |
+| `tests/lib` | `github.com/google/googletest` | — | C++ test framework |
+
+Update a submodule:
+```bash
+cd mods/silo
+git checkout main && git pull
+cd ../..
+git add mods/silo
+git commit -m "chore: update silo submodule"
+```
+
+Initialize all submodules: `git submodule update --init --recursive`
+
+## Key Addon Modules
+
+### ztools (`mods/ztools/`)
+
+Command provider (NOT a workbench). Injects tools into PartDesign, Assembly, and Spreadsheet contexts via `_ZToolsManipulator` (WorkbenchManipulator) and `injectEditingCommands()`.
+
+Commands: `ZTools_DatumCreator`, `ZTools_EnhancedPocket`, `ZTools_RotatedLinearPattern`, `ZTools_AssemblyLinearPattern`, `ZTools_AssemblyPolarPattern`, spreadsheet formatting (Bold, Italic, Underline, alignment, colors, QuickAlias).
+
+Source: `mods/ztools/ztools/ztools/commands/` (note the double `ztools` nesting).
+
+### Silo (`mods/silo/`)
+
+PLM workbench with 14 commands for parts lifecycle management. Go REST API server + PostgreSQL + MinIO backend. FreeCAD client communicates via shared `silo-client` submodule.
+
+Silo origin detection: `silo_origin.py:ownsDocument()` checks for `SiloItemId`/`SiloPartNumber` properties on the active document.
+
+### SDK (`mods/sdk/`)
+
+Stable API contract for addons. Provides wrappers for editing contexts, theme tokens (Catppuccin Mocha YAML palette), FileOrigin registration, and deferred dock panels. Addons should use `kindred_sdk.*` instead of `FreeCADGui.*` internals where possible.
+
+## Theme
+
+- **Canonical source:** `src/Gui/Stylesheets/KindredCreate.qss`
+- The PreferencePacks copy at `src/Gui/PreferencePacks/KindredCreate/KindredCreate.qss` is **generated at build time** via `configure_file()`. Only edit the Stylesheets copy.
+- Color palette: Catppuccin Mocha (26 colors + 14 semantic roles, defined in `mods/sdk/kindred_sdk/palettes/catppuccin-mocha.yaml`)
+- Default preferences: `src/Gui/PreferencePacks/KindredCreate/KindredCreate.cfg`
+
+## Git Conventions
+
+### Branch Names
+
+`type/kebab-case-description`
+
+Types: `feat/`, `fix/`, `chore/`, `docs/`, `refactor/`, `art/`
+
+### Commit Messages
+
+[Conventional Commits](https://www.conventionalcommits.org/):
+
+```
+type(scope): lowercase imperative description
+```
+
+| Prefix | Purpose |
+|--------|---------|
+| `feat:` | New feature |
+| `fix:` | Bug fix |
+| `chore:` | Maintenance, dependencies |
+| `docs:` | Documentation only |
+| `art:` | Icons, theme, visual assets |
+| `refactor:` | Code restructuring |
+
+Scopes: `solver`, `sketcher`, `editing-context`, `toolbar`, `ztools`, `silo`, `breadcrumb`, `gui`, `assembly`, `ci`, `theme`, `quicknav`, or omitted.
+
+### PR Workflow
+
+1. Create a branch from `main`: `git checkout -b feat/my-feature main`
+2. Commit with conventional commit messages
+3. Push and open a PR against `main` via Gitea (or `tea pulls create`)
+4. CI runs automatically on PRs
+
+### Code Style
+
+- **C++:** clang-format (`.clang-format`), clang-tidy (`.clang-tidy`)
+- **Python:** black (100-char line length), pylint (`.pylintrc`)
+- **Pre-commit hooks:** `pre-commit install` (runs clang-format, black, trailing-whitespace, etc.)
+
+## CI/CD
+
+- **Build:** `.gitea/workflows/build.yml` — runs on pushes to `main` and on PRs
+- **Release:** `.gitea/workflows/release.yml` — triggered by `v*` tags, builds AppImage and .deb
+- **Platform:** Currently Linux x86_64 only in CI; other platforms have presets but no runners yet
+
+## Documentation
+
+| Document | Content |
+|----------|---------|
+| `README.md` | Project overview, installation, usage |
+| `CONTRIBUTING.md` | Branch workflow, commit conventions, code style |
+| `docs/ARCHITECTURE.md` | Bootstrap flow, addon lifecycle, source layout |
+| `docs/COMPONENTS.md` | Feature inventory (ztools, Silo, origin, theme, icons) |
+| `docs/KNOWN_ISSUES.md` | Known issues, incomplete features, next steps |
+| `docs/INTEGRATION_PLAN.md` | 5-layer architecture, phase status |
+| `docs/CI_CD.md` | Build and release workflows |
+| `docs/KC_SPECIFICATION.md` | .kc file format specification |
+| `docs/UPSTREAM.md` | FreeCAD upstream merge strategy |
+| `docs/INTER_SOLVER.md` | Assembly solver integration |
+| `docs/BOM_MERGE.md` | BOM-Assembly bridge specification |
+
+The `docs/src/` directory contains an mdBook site with detailed guides organized by topic (architecture, development, guide, reference, silo-server, solver).
+
+## Issue Tracker
+
+Issues are tracked on Gitea at `git.kindred-systems.com/kindred/create/issues`. Use the `tea` CLI for local interaction:
+
+```bash
+tea issues              # List open issues
+tea issues 123          # View issue #123 details
+tea pulls create        # Create a PR
+```
+
+## Known Issues and Pitfalls
+
+1. **Silo auth not production-hardened** — LDAP/OIDC backends are coded but need infrastructure deployment
+2. **No unit tests** for ztools/Silo FreeCAD commands or Go backend
+3. **Assembly solver datum handling is minimal** — joints referencing datum planes/points may produce incorrect placement
+4. **PartDesign menu insertion fragility** — `_ZToolsPartDesignManipulator.modifyMenuBar()` inserts after `PartDesign_Boolean`; upstream renames break silently
+5. **`Silo_BOM` requires Silo-tracked document** — unregistered documents show a warning with no registration path
+6. **QSS edits** — only edit `src/Gui/Stylesheets/KindredCreate.qss`; the PreferencePacks copy is auto-generated

CMakeLists.txt

@@ -53,7 +53,7 @@ project(KindredCreate)
 # Kindred Create version
 set(KINDRED_CREATE_VERSION_MAJOR "0")
 set(KINDRED_CREATE_VERSION_MINOR "1")
-set(KINDRED_CREATE_VERSION_PATCH "0")
+set(KINDRED_CREATE_VERSION_PATCH "5")
 set(KINDRED_CREATE_VERSION "${KINDRED_CREATE_VERSION_MAJOR}.${KINDRED_CREATE_VERSION_MINOR}.${KINDRED_CREATE_VERSION_PATCH}")
 
 # Underlying FreeCAD version

README.md

@@ -2,7 +2,7 @@
 
 **An engineering-focused parametric 3D CAD platform built on FreeCAD 1.0+**
 
-Kindred Create 0.1.0 | FreeCAD 1.2.0 base
+Kindred Create 0.1.5 | FreeCAD 1.2.0 base
 
 [Website](https://www.kindred-systems.com/create) |
 [Downloads](https://git.kindred-systems.com/kindred/create/releases) |

docs/src/SUMMARY.md

@@ -12,6 +12,7 @@
 - [Workbenches](./guide/workbenches.md)
   - [ztools](./guide/ztools.md)
   - [Silo](./guide/silo.md)
+  - [Document Templates](./guide/templates.md)
 
 # Architecture
 
@@ -49,6 +50,16 @@
 - [Solver Service](./silo-server/SOLVER.md)
 - [Roadmap](./silo-server/ROADMAP.md)
 
+# Kindred Solver
+
+- [Overview](./solver/overview.md)
+- [Expression DAG](./solver/expression-dag.md)
+- [Constraints](./solver/constraints.md)
+- [Solving Algorithms](./solver/solving.md)
+- [Diagnostics](./solver/diagnostics.md)
+- [Assembly Integration](./solver/assembly-integration.md)
+- [Writing a Custom Solver](./solver/writing-a-solver.md)
+
 # Reference
 
 - [Configuration](./reference/configuration.md)

docs/src/development/build-system.md

@@ -13,7 +13,7 @@ Kindred Create uses **CMake** for build configuration, **pixi** (conda-based) fo
 ## CMake configuration
 
 The root `CMakeLists.txt` defines:
-- **Kindred Create version:** `0.1.0` (via `KINDRED_CREATE_VERSION`)
+- **Kindred Create version:** `0.1.5` (via `KINDRED_CREATE_VERSION`)
 - **FreeCAD base version:** `1.0.0` (via `FREECAD_VERSION`)
 - CMake policy settings for compatibility
 - ccache auto-detection
@@ -25,7 +25,7 @@ The root `CMakeLists.txt` defines:
 The version flows from CMake to Python via `configure_file()`:
 
 ```
-CMakeLists.txt (KINDRED_CREATE_VERSION = "0.1.0")
+CMakeLists.txt (KINDRED_CREATE_VERSION = "0.1.5")
     → src/Mod/Create/version.py.in (template)
     → build/*/Mod/Create/version.py (generated)
     → update_checker.py (imports VERSION)

docs/src/development/gui-build-integration.md

@@ -157,7 +157,7 @@ Edit only the canonical file in `Stylesheets/` — the preference pack copy is g
 Defined in the top-level `CMakeLists.txt` and injected as compiler definitions:
 
 ```cmake
-set(KINDRED_CREATE_VERSION "0.1.0")
+set(KINDRED_CREATE_VERSION "0.1.5")
 set(FREECAD_VERSION "1.0.0")
 
 add_definitions(-DKINDRED_CREATE_VERSION="${KINDRED_CREATE_VERSION}")

docs/src/guide/silo.md

@@ -53,6 +53,7 @@ The silo-mod repository was split from a monorepo into three repos: `silo-client
 | `Silo_TagProjects` | Multi-select dialog for assigning project tags to items |
 | `Silo_Rollback` | Select a previous revision and create a new revision from that point with optional comment |
 | `Silo_SetStatus` | Change revision lifecycle status: draft → review → released → obsolete |
+| `Silo_SaveAsTemplate` | Save a copy of the current document as a reusable [template](./templates.md) with metadata |
 
 ### Administration
 
@@ -129,9 +130,11 @@ mods/silo/
 ├── freecad/
 │   ├── InitGui.py             # SiloWorkbench registration
 │   ├── schema_form.py         # Schema-driven item creation dialog (SchemaFormDialog)
-│   ├── silo_commands.py       # 14 commands + dock widgets
+│   ├── silo_commands.py       # 15 commands + dock widgets
 │   ├── silo_origin.py         # FileOrigin backend
 │   ├── silo_start.py          # Native start panel (database items, activity feed)
+│   ├── templates.py           # Template discovery, filtering, injection
+│   ├── templates/             # System template .kc files + CLI injection tool
 │   └── resources/icons/       # 10 silo-*.svg icons
 ├── silo-client/               # Shared Python API client (nested submodule)
 │   └── silo_client/

docs/src/guide/templates.md

@@ -0,0 +1,140 @@
+# Document Templates
+
+Templates let you create new parts and assemblies from pre-configured `.kc` files. Instead of starting from a bare `App::Part` or `Assembly::AssemblyObject`, a template can include predefined tree structures, jobs, metadata, and workbench-specific features.
+
+## How templates work
+
+A template is a normal `.kc` file with an extra `silo/template.json` descriptor inside the ZIP archive. When you select a template during **Silo > New**:
+
+1. The template `.kc` is **copied** to the canonical file path
+2. `silo/template.json` and `silo/manifest.json` are **stripped** from the copy
+3. The document is **opened** in FreeCAD
+4. Silo properties (part number, item ID, revision, type) are **stamped** onto the root object
+5. On **save**, `kc_format.py` auto-creates a fresh manifest
+
+The original template file is never modified.
+
+## Using templates
+
+### Creating a new item from a template
+
+1. **Silo > New** (Ctrl+N)
+2. Select an **Item Type** (Part, Assembly, etc.)
+3. The **Template** dropdown shows templates matching the selected type and category
+4. Select a template (or leave as "No template" for a blank document)
+5. Fill in the remaining fields and click **Create**
+
+The template combo updates automatically when you change the item type or category.
+
+### Saving a document as a template
+
+1. Open the document you want to use as a template
+2. **Silo > Save as Template**
+3. Fill in the template metadata:
+   - **Name** — display name shown in the template picker (pre-filled from document label)
+   - **Description** — what the template is for
+   - **Item Types** — which types this template applies to (part, assembly, etc.)
+   - **Categories** — category prefix filter (e.g. `F`, `M01`); leave empty for all categories
+   - **Author** — pre-filled from your Silo login
+   - **Tags** — comma-separated search tags
+4. Click **Save Template**
+5. Optionally upload to Silo for team sharing
+
+The template is saved as a copy to your personal templates directory. The original document is unchanged.
+
+## Template search paths
+
+Templates are discovered from three locations, checked in order. Later paths shadow earlier ones by name (so you can override a system template with a personal one).
+
+| Priority | Path | Purpose |
+|----------|------|---------|
+| 1 (lowest) | `mods/silo/freecad/templates/` | System templates shipped with the addon |
+| 2 | `~/.local/share/FreeCAD/Templates/` | Personal templates (sister to `Macro/`) |
+| 3 (highest) | `~/projects/templates/` | Org-shared project templates |
+
+The personal templates directory (`Templates/`) is created automatically when you first save a template. It lives alongside the `Macro/` directory in your FreeCAD user data.
+
+## Template descriptor schema
+
+The `silo/template.json` file inside the `.kc` ZIP has the following structure:
+
+```json
+{
+  "template_version": "1.0",
+  "name": "Sheet Metal Part",
+  "description": "Body with SheetMetal base feature and laser-cut job",
+  "item_types": ["part"],
+  "categories": [],
+  "icon": "sheet-metal",
+  "author": "Kindred Systems",
+  "tags": ["sheet metal", "fabrication"]
+}
+```
+
+| Field | Type | Required | Description |
+|-------|------|----------|-------------|
+| `template_version` | string | yes | Schema version, currently `"1.0"` |
+| `name` | string | yes | Display name in the template picker |
+| `description` | string | no | Human-readable purpose |
+| `item_types` | string[] | yes | Controls visibility — `["part"]`, `["assembly"]`, or both |
+| `categories` | string[] | no | Category prefix filter. Empty array means all categories |
+| `icon` | string | no | Icon identifier (reserved for future use) |
+| `author` | string | no | Template author |
+| `tags` | string[] | no | Searchable metadata tags |
+
+### Filtering rules
+
+- **item_types**: The template only appears when the selected item type is in this list
+- **categories**: If non-empty, the template only appears when the selected category starts with one of the listed prefixes. An empty list means the template is available for all categories
+
+## Creating templates from the command line
+
+The `inject_template.py` CLI tool can inject `silo/template.json` into any `.kc` file:
+
+```bash
+cd mods/silo/freecad/templates/
+
+# Create a template from an existing .kc file
+python inject_template.py my-part.kc "My Custom Part" \
+    --type part \
+    --description "Part with custom features" \
+    --author "Your Name" \
+    --tag "custom"
+
+# Assembly template
+python inject_template.py my-assembly.kc "My Assembly" \
+    --type assembly \
+    --description "Assembly with predefined joint groups"
+
+# Template with category filtering
+python inject_template.py sheet-metal.kc "Sheet Metal Part" \
+    --type part \
+    --category S \
+    --category X \
+    --tag "sheet metal" \
+    --tag "fabrication"
+```
+
+## Module structure
+
+```
+mods/silo/freecad/
+├── templates.py               # Discovery, filtering, injection helpers
+├── templates/
+│   └── inject_template.py     # CLI tool for injecting template.json
+├── schema_form.py             # Template combo in New Item form
+└── silo_commands.py           # SaveAsTemplateDialog, Silo_SaveAsTemplate,
+                               # SiloSync.create_document_from_template()
+```
+
+### Key functions
+
+| Function | File | Purpose |
+|----------|------|---------|
+| `discover_templates()` | `templates.py` | Scan search paths for `.kc` files with `silo/template.json` |
+| `filter_templates()` | `templates.py` | Filter by item type and category prefix |
+| `inject_template_json()` | `templates.py` | Inject/replace `silo/template.json` in a `.kc` ZIP |
+| `get_default_template_dir()` | `templates.py` | Returns `{userAppData}/Templates/`, creating if needed |
+| `get_search_paths()` | `templates.py` | Returns the 3-tier search path list |
+| `create_document_from_template()` | `silo_commands.py` | Copy template, strip identity, stamp Silo properties |
+| `_clean_template_zip()` | `silo_commands.py` | Strip `silo/template.json` and `silo/manifest.json` from a copy |

docs/src/quicknav/SPEC.md

@@ -0,0 +1,441 @@
+# QuickNav — Keyboard Navigation Addon Specification
+
+**Addon name:** QuickNav
+**Type:** Pure Python FreeCAD addon (no C++ required)
+**Compatibility:** FreeCAD 1.0+, Kindred Create 0.1+
+**Location:** `mods/quicknav/`
+
+---
+
+## 1. Overview
+
+QuickNav provides keyboard-driven command access for FreeCAD and Kindred Create. It replaces mouse-heavy toolbar navigation with a numbered key system organized by workbench and command grouping. The addon is activated by loading its workbench and toggled on/off with the `0` key.
+
+### Design Goals
+
+- Numbers `1-9` execute commands within the active command grouping
+- `Shift+1-9` switches command grouping within the active workbench
+- `Ctrl+1-9` switches workbench context
+- All groupings and workbenches are ordered by most-recently-used (MRU) history
+- History is unlimited internally, top 9 shown, remainder scrollable/clickable
+- Mouse interaction remains fully functional — QuickNav is purely additive
+- Configuration persisted via `FreeCAD.ParamGet()`
+
+---
+
+## 2. Terminology
+
+| Term | Definition |
+|------|-----------|
+| **Workbench** | A FreeCAD workbench (Sketcher, PartDesign, Assembly, etc.). Fixed assignment to Ctrl+N slots. |
+| **Command Grouping** | A logical group of commands within a workbench, mapped from existing FreeCAD toolbar groupings. Max 9 per tier. |
+| **Active Grouping** | The left-most visible grouping in the navigation bar. Its commands are accessible via `1-9`. |
+| **Navigation Bar** | Bottom toolbar displaying the current state: active workbench, groupings, and numbered commands. |
+| **MRU Stack** | Most-recently-used ordering. Position 0 = currently active, 1 = previously active, etc. |
+| **Tier** | When a workbench has >9 command groupings, they are split: Tier 1 (most common 9), Tier 2 (next 9). |
+
+---
+
+## 3. Key Bindings
+
+### 3.1 Mode Toggle
+
+| Key | Action |
+|-----|--------|
+| `0` | Toggle QuickNav on/off. When off, all QuickNav key interception is disabled and the navigation bar hides. |
+
+### 3.2 Command Execution
+
+| Key | Action |
+|-----|--------|
+| `1-9` | Execute the Nth command in the active grouping. If the command is auto-executable (e.g., Pad after closed sketch), execute immediately. Otherwise, enter tool mode (same as clicking the toolbar button). |
+
+### 3.3 Grouping Navigation
+
+| Key | Action |
+|-----|--------|
+| `Shift+1-9` | Switch to the Nth command grouping (MRU ordered) within the current workbench. The newly activated grouping moves to position 0 in the MRU stack. |
+| `Shift+Left/Right` | Scroll through groupings beyond the visible 9. |
+
+### 3.4 Workbench Navigation
+
+| Key | Action |
+|-----|--------|
+| `Ctrl+1` | Sketcher |
+| `Ctrl+2` | Part Design |
+| `Ctrl+3` | Assembly |
+| `Ctrl+4` | Spreadsheet |
+| `Ctrl+5` | TechDraw |
+| `Ctrl+6-9` | User-configurable / additional workbenches |
+
+Switching workbench via `Ctrl+N` also restores that workbench's last-active command grouping.
+
+---
+
+## 4. Navigation Bar
+
+The navigation bar is a `QToolBar` positioned at the bottom of the main window (replacing or sitting alongside FreeCAD's default bottom toolbar area).
+
+### 4.1 Layout
+
+```
+┌─────────────────────────────────────────────────────────────────────┐
+│ [WB: Sketcher] │ ❶ Primitives │ ② Constraints │ ③ Dimensions │ ◀▶ │
+│                │ 1:Line 2:Rect 3:Circle 4:Arc 5:Point 6:Slot ...  │
+└─────────────────────────────────────────────────────────────────────┘
+```
+
+- **Left section:** Current workbench name with Ctrl+N hint
+- **Middle section (top row):** Command groupings, MRU ordered. Active grouping is ❶ (filled circle), others are ②③ etc. Scrollable horizontally if >9.
+- **Middle section (bottom row):** Commands within the active grouping, numbered 1-9
+- **Right section:** Scroll arrows for overflow groupings
+
+### 4.2 Visual States
+
+- **Active grouping:** Bold text, filled number badge, Catppuccin Mocha `blue` (#89b4fa) accent
+- **Inactive groupings:** Normal text, outlined number badge, `surface1` (#45475a) text
+- **Hovered command:** `surface2` (#585b70) background highlight
+- **Active command (tool in use):** `green` (#a6e3a1) underline indicator
+
+### 4.3 Mouse Interaction
+
+- Click any grouping to activate it (equivalent to Shift+N)
+- Click any command to execute it (equivalent to pressing N)
+- Scroll wheel on grouping area to cycle through overflow groupings
+- Click scroll arrows to page through overflow
+
+---
+
+## 5. Workbench Command Groupings
+
+Each workbench's existing FreeCAD toolbars map to command groupings. Where a workbench has >9 toolbars, split into Tier 1 (default, most common) and Tier 2 (accessible via scrolling or `Shift+Left/Right`).
+
+### 5.1 Sketcher (Ctrl+1)
+
+| Grouping | Commands (1-9) |
+|----------|---------------|
+| Primitives | Line, Rectangle, Circle, Arc, Point, Slot, B-Spline, Polyline, Ellipse |
+| Constraints | Coincident, Horizontal, Vertical, Parallel, Perpendicular, Tangent, Equal, Symmetric, Block |
+| Dimensions | Distance, Horizontal Distance, Vertical Distance, Radius, Diameter, Angle, Lock, Constrain Refraction |
+| Construction | Toggle Construction, External Geometry, Carbon Copy, Offset, Trim, Extend, Split |
+| Tools | Mirror, Array (Linear), Array (Polar), Move, Rotate, Scale, Close Shape, Connect Edges |
+
+### 5.2 Part Design (Ctrl+2)
+
+| Grouping | Commands (1-9) |
+|----------|---------------|
+| Additive | Pad, Revolution, Additive Loft, Additive Pipe, Additive Helix, Additive Box, Additive Cylinder, Additive Sphere, Additive Cone |
+| Subtractive | Pocket, Hole, Groove, Subtractive Loft, Subtractive Pipe, Subtractive Helix, Subtractive Box, Subtractive Cylinder, Subtractive Sphere |
+| Datums | New Sketch, Datum Plane, Datum Line, Datum Point, Shape Binder, Sub-Shape Binder, ZTools Datum Creator, ZTools Datum Manager |
+| Transformations | Mirrored, Linear Pattern, Polar Pattern, MultiTransform, ZTools Rotated Linear Pattern |
+| Modeling | Fillet, Chamfer, Draft, Thickness, Boolean, ZTools Enhanced Pocket |
+
+### 5.3 Assembly (Ctrl+3)
+
+| Grouping | Commands (1-9) |
+|----------|---------------|
+| Components | Insert Component, Create Part, Create Assembly, Ground, BOM |
+| Joints | Fixed, Revolute, Cylindrical, Slider, Ball, Planar, Distance, Angle, Parallel |
+| Patterns | ZTools Linear Pattern, ZTools Polar Pattern |
+
+### 5.4 Spreadsheet (Ctrl+4)
+
+| Grouping | Commands (1-9) |
+|----------|---------------|
+| Editing | Merge Cells, Split Cell, Alias, Import CSV, Export CSV |
+| Formatting | Bold, Italic, Underline, Align Left, Align Center, Align Right, BG Color, Text Color, Quick Alias |
+
+### 5.5 TechDraw (Ctrl+5)
+
+Groupings derived from TechDraw's existing toolbars at runtime.
+
+> **Note:** The exact command lists above are initial defaults. The addon discovers available commands from each workbench's toolbar structure at activation time and falls back to these defaults only if discovery fails.
+
+---
+
+## 6. MRU History Behavior
+
+### 6.1 Grouping History (per workbench)
+
+Each workbench maintains its own grouping MRU stack.
+
+- When a grouping is activated (via `Shift+N` or mouse click), it moves to position 0
+- The previously active grouping moves to position 1, everything else shifts down
+- Position 0 is always the active grouping (already selected, shown leftmost)
+- `Shift+1` is a no-op (already active), `Shift+2` activates the previous grouping, etc.
+
+### 6.2 Workbench History
+
+- Workbenches have fixed Ctrl+N assignments (not MRU ordered)
+- However, each workbench remembers its last-active grouping
+- Switching to a workbench restores its last-active grouping as position 0
+
+### 6.3 Persistence
+
+Stored in `FreeCAD.ParamGet("User parameter:BaseApp/Preferences/Mod/QuickNav")`:
+
+| Parameter | Type | Description |
+|-----------|------|-------------|
+| `Enabled` | Bool | Whether QuickNav is currently active |
+| `GroupHistory/<Workbench>` | String | Semicolon-delimited list of grouping names in MRU order |
+| `LastGrouping/<Workbench>` | String | Name of the last-active grouping per workbench |
+| `CustomSlots/Ctrl6` through `Ctrl9` | String | Workbench names for user-configurable slots |
+
+---
+
+## 7. Auto-Execution Logic
+
+When a command is invoked via number key, QuickNav checks if the command can be auto-executed:
+
+### 7.1 Auto-Execute Conditions
+
+A command auto-executes (runs and completes without entering a persistent mode) when:
+
+1. **Pad/Pocket after closed sketch:** If the active body has a sketch that was just closed (sketch edit mode exited with a closed profile), pressing the Pad or Pocket command key creates the feature with default parameters. The task panel still opens for parameter adjustment.
+2. **Boolean operations:** If exactly two bodies/shapes are selected, boolean commands execute with defaults.
+3. **Constraint application:** If appropriate geometry is pre-selected in Sketcher, constraint commands apply immediately.
+
+### 7.2 Mode-Entry (Default)
+
+All other commands enter their standard FreeCAD tool mode — identical to clicking the toolbar button. The user interacts with the 3D view and/or task panel as normal.
+
+---
+
+## 8. Key Event Handling
+
+### 8.1 Event Filter Architecture
+
+```python
+class QuickNavEventFilter(QObject):
+    """Installed on FreeCAD's main window via installEventFilter().
+
+    Intercepts KeyPress events when QuickNav is active.
+    Passes through all events when QuickNav is inactive.
+    """
+
+    def eventFilter(self, obj, event):
+        if event.type() != QEvent.KeyPress:
+            return False
+        if not self._active:
+            return False
+
+        # Don't intercept when a text input widget has focus
+        focused = QApplication.focusWidget()
+        if isinstance(focused, (QLineEdit, QTextEdit, QPlainTextEdit, QSpinBox, QDoubleSpinBox)):
+            return False
+
+        # Don't intercept when task panel input fields are focused
+        if self._is_task_panel_input(focused):
+            return False
+
+        key = event.key()
+        modifiers = event.modifiers()
+
+        if key == Qt.Key_0 and modifiers == Qt.NoModifier:
+            self.toggle_active()
+            return True
+
+        if key >= Qt.Key_1 and key <= Qt.Key_9:
+            n = key - Qt.Key_0
+            if modifiers == Qt.ControlModifier:
+                self.switch_workbench(n)
+                return True
+            elif modifiers == Qt.ShiftModifier:
+                self.switch_grouping(n)
+                return True
+            elif modifiers == Qt.NoModifier:
+                self.execute_command(n)
+                return True
+
+        return False  # Pass through all other keys
+```
+
+### 8.2 Conflict Resolution
+
+QuickNav's event filter takes priority when active. FreeCAD's existing keybindings for `Ctrl+1` through `Ctrl+9` (if any) are overridden while QuickNav is enabled. The original bindings are restored when QuickNav is toggled off or unloaded.
+
+Existing `Shift+` and bare number key bindings in FreeCAD are similarly overridden only while QuickNav is active. This is safe because:
+- FreeCAD does not use bare number keys as shortcuts by default
+- Shift+number is not commonly bound in default FreeCAD
+
+### 8.3 Input Widget Safety
+
+The event filter must NOT intercept keys when the user is:
+- Typing in the Python console
+- Entering values in the task panel (dimensions, parameters)
+- Editing spreadsheet cells
+- Typing in any `QLineEdit`, `QTextEdit`, `QSpinBox`, or `QDoubleSpinBox`
+- Using the Sketcher's inline dimension input
+
+---
+
+## 9. Addon Structure
+
+```
+mods/quicknav/
+├── package.xml              # FreeCAD addon manifest with <kindred> extension
+├── Init.py                  # Non-GUI initialization (no-op)
+├── InitGui.py               # Registers QuickNavWorkbench
+├── quicknav/
+│   ├── __init__.py
+│   ├── core.py              # QuickNavManager singleton — orchestrates state
+│   ├── event_filter.py      # QuickNavEventFilter (QObject)
+│   ├── nav_bar.py           # NavigationBar (QToolBar subclass)
+│   ├── workbench_map.py     # Fixed workbench → Ctrl+N mapping + grouping discovery
+│   ├── history.py           # MRU stack with ParamGet persistence
+│   ├── auto_exec.py         # Auto-execution condition checks
+│   ├── commands.py          # FreeCAD command wrappers (QuickNav_Toggle, etc.)
+│   └── resources/
+│       ├── icons/           # Number badge SVGs, QuickNav icon
+│       └── theme.py         # Catppuccin Mocha color tokens
+└── tests/
+    └── test_history.py      # MRU stack unit tests
+```
+
+### 9.1 Manifest
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<package format="1">
+  <name>QuickNav</name>
+  <description>Keyboard-driven toolbar navigation</description>
+  <version>0.1.0</version>
+  <maintainer email="dev@kindred-systems.com">Kindred Systems</maintainer>
+  <license>LGPL-2.1</license>
+  <content>
+    <workbench>
+      <classname>QuickNavWorkbench</classname>
+    </workbench>
+  </content>
+  <kindred>
+    <min_create_version>0.1.0</min_create_version>
+    <load_priority>10</load_priority>
+    <pure_python>true</pure_python>
+    <dependencies>
+      <dependency>sdk</dependency>
+    </dependencies>
+  </kindred>
+</package>
+```
+
+### 9.2 Activation
+
+QuickNav activates when its workbench is loaded (via the addon loader or manual activation). It installs the event filter on the main window and creates the navigation bar. The workbench itself is invisible — it does not add its own toolbars or menus beyond the navigation bar. It acts as a transparent overlay on whatever workbench the user is actually working in.
+
+```python
+class QuickNavWorkbench(Gui.Workbench):
+    """Invisible workbench that installs QuickNav on load.
+
+    QuickNav doesn't replace the active workbench — it layers on top.
+    Loading QuickNav installs the event filter and nav bar, then
+    immediately re-activates the previously active workbench.
+    """
+
+    def Initialize(self):
+        QuickNavManager.instance().install()
+
+    def Activated(self):
+        # Re-activate the previous workbench so QuickNav is transparent
+        prev = QuickNavManager.instance().previous_workbench
+        if prev:
+            Gui.activateWorkbench(prev)
+
+    def Deactivated(self):
+        pass
+
+    def GetClassName(self):
+        return "Gui::PythonWorkbench"
+```
+
+**Alternative (preferred for Create):** Instead of a workbench, QuickNav can be activated directly from `Create/InitGui.py` at boot, gated by the `Enabled` preference. This avoids the workbench-switching dance entirely. The `QuickNavWorkbench` registration is kept for standalone FreeCAD compatibility.
+
+---
+
+## 10. Command Discovery
+
+At activation time, QuickNav introspects each workbench's toolbars to build the command grouping map.
+
+```python
+def discover_groupings(workbench_name: str) -> list[CommandGrouping]:
+    """Discover command groupings from a workbench's toolbar structure.
+
+    1. Temporarily activate the workbench (if not already active)
+    2. Enumerate QToolBars from the main window
+    3. Map toolbar name → list of QAction names
+    4. Filter out non-command actions (separators, widgets)
+    5. Split into tiers if >9 groupings
+    6. Restore the previously active workbench
+    """
+```
+
+### 10.1 Fallback Defaults
+
+If toolbar discovery fails (workbench not initialized, empty toolbars), QuickNav falls back to the hardcoded groupings in Section 5. These are stored as a Python dict in `workbench_map.py`.
+
+### 10.2 ZTools Integration
+
+ZTools commands injected via `WorkbenchManipulator` appear in the discovered toolbars and are automatically included in the relevant groupings. No special handling is needed — QuickNav discovers commands after all manipulators have run.
+
+---
+
+## 11. FreeCAD Compatibility
+
+QuickNav is designed as a standalone FreeCAD addon that works without Kindred Create or the SDK.
+
+| Feature | FreeCAD | Kindred Create |
+|---------|---------|----------------|
+| Core navigation (keys, nav bar) | ✅ | ✅ |
+| Catppuccin Mocha theming | ❌ (uses Qt defaults) | ✅ (via SDK theme tokens) |
+| Auto-boot on startup | ❌ (manual workbench activation) | ✅ (via addon loader) |
+| ZTools commands in groupings | ❌ (not present) | ✅ (discovered from manipulated toolbars) |
+
+The SDK dependency is optional — QuickNav checks for `kindred_sdk` availability and degrades gracefully:
+
+```python
+try:
+    from kindred_sdk.theme import get_theme_tokens
+    THEME = get_theme_tokens()
+except ImportError:
+    THEME = None  # Use Qt default palette
+```
+
+---
+
+## 12. Implementation Phases
+
+### Phase 1: Core Infrastructure
+- Event filter with key interception and input widget safety
+- QuickNavManager singleton with toggle on/off
+- Navigation bar widget (QToolBar) with basic layout
+- Hardcoded workbench/grouping maps from Section 5
+- ParamGet persistence for enabled state
+
+### Phase 2: Dynamic Discovery
+- Toolbar introspection for command grouping discovery
+- MRU history with persistence
+- Grouping overflow scrolling
+- Workbench restore (last-active grouping per workbench)
+
+### Phase 3: Auto-Execution
+- Context-aware auto-execute logic
+- Sketcher closed-profile detection for Pad/Pocket
+- Pre-selection constraint application
+
+### Phase 4: Polish
+- Number badge SVG icons
+- Catppuccin Mocha theming (conditional on SDK)
+- Scroll animations
+- Settings dialog (custom Ctrl+6-9 assignments)
+- FreeCAD standalone packaging
+
+---
+
+## 13. Open Questions
+
+1. **Tier switching UX:** When a workbench has >9 groupings split into tiers, should `Shift+0` toggle between tiers, or should tiers be purely a scroll/mouse concept?
+
+2. **Visual number badges:** Should the commands in the nav bar show keycap-style badges (like `⌨ 1`) or just prepend the number (`1: Line`)?
+
+3. **Sketcher inline dimension input:** FreeCAD's Sketcher has an inline dimension entry that isn't a standard QLineEdit. Need to verify the event filter correctly identifies and skips this widget.
+
+4. **Ctrl+N conflicts with Create shortcuts:** Verify that Create/Silo don't already bind Ctrl+1 through Ctrl+9. The Silo toggle uses Ctrl+O/S/N, so these should be clear.

docs/src/reference/configuration.md

@@ -77,7 +77,7 @@ Defined in the root `CMakeLists.txt`:
 
 | Constant | Value | Description |
 |----------|-------|-------------|
-| `KINDRED_CREATE_VERSION` | `0.1.0` | Kindred Create version |
+| `KINDRED_CREATE_VERSION` | `0.1.5` | Kindred Create version |
 | `FREECAD_VERSION` | `1.0.0` | FreeCAD base version |
 
 These are injected into `src/Mod/Create/version.py` at build time via `version.py.in`.

docs/src/solver/assembly-integration.md

@@ -0,0 +1,219 @@
+# Assembly Integration
+
+The Kindred solver integrates with FreeCAD's Assembly workbench through the KCSolve pluggable solver framework. This page describes the bridge layer, preference system, and interactive drag protocol.
+
+## KindredSolver class
+
+**Source:** `mods/solver/kindred_solver/solver.py`
+
+`KindredSolver` subclasses `kcsolve.IKCSolver` and implements the solver interface:
+
+```python
+class KindredSolver(kcsolve.IKCSolver):
+    def name(self):
+        return "Kindred (Newton-Raphson)"
+
+    def supported_joints(self):
+        return list(_SUPPORTED)  # 20 of 24 BaseJointKind values
+
+    def solve(self, ctx):        # Static solve
+    def diagnose(self, ctx):     # Constraint analysis
+    def pre_drag(self, ctx, drag_parts):   # Begin drag session
+    def drag_step(self, drag_placements):  # Mouse move during drag
+    def post_drag(self):                   # End drag session
+    def is_deterministic(self):  # Returns True
+```
+
+### Registration
+
+The solver is registered at addon load time via `Init.py`:
+
+```python
+import kcsolve
+from kindred_solver import KindredSolver
+kcsolve.register_solver("kindred", KindredSolver)
+```
+
+The `mods/solver/` directory is a FreeCAD addon discovered by the addon loader through its `package.xml` manifest.
+
+### Supported joints
+
+The Kindred solver handles 20 of the 24 `BaseJointKind` values. The remaining 4 are stubs that produce no residuals:
+
+| Supported | Stub (no residuals) |
+|-----------|-------------------|
+| Coincident, PointOnLine, PointInPlane, Concentric, Tangent, Planar, LineInPlane, Parallel, Perpendicular, Angle, Fixed, Revolute, Cylindrical, Slider, Ball, Screw, Universal, Gear, RackPinion, DistancePointPoint | Cam, Slot, DistanceCylSph, Custom |
+
+### Joint limits
+
+Joint travel limits (`Constraint.limits`) are accepted but not enforced. The solver logs a warning once per instance when limits are encountered. Enforcing inequality constraints requires active-set or barrier-method extensions beyond the current Newton-Raphson formulation.
+
+## Solver selection
+
+### C++ preference
+
+`AssemblyObject::getOrCreateSolver()` reads the user preference to select the solver backend:
+
+```cpp
+ParameterGrp::handle hGrp = App::GetApplication().GetParameterGroupByPath(
+    "User parameter:BaseApp/Preferences/Mod/Assembly");
+std::string solverName = hGrp->GetASCII("Solver", "");
+solver_ = KCSolve::SolverRegistry::instance().get(solverName);
+```
+
+An empty string (`""`) returns the registry default (the first solver registered, which is OndselSolver). Setting `"kindred"` selects the Kindred solver.
+
+`resetSolver()` clears the cached solver instance so the next solve picks up preference changes.
+
+### Preferences UI
+
+The Assembly preferences page (`Edit > Preferences > Assembly`) includes a "Solver backend" combo box populated from the registry at load time:
+
+- **Default** -- empty string, uses the registry default (OndselSolver)
+- **OndselSolver (Lagrangian)** -- `"ondsel"`
+- **Kindred (Newton-Raphson)** -- `"kindred"` (available when the solver addon is loaded)
+
+The preference is stored as `Mod/Assembly/Solver` in the FreeCAD parameter system.
+
+### Programmatic switching
+
+From the Python console:
+
+```python
+import FreeCAD
+pref = FreeCAD.ParamGet("User parameter:BaseApp/Preferences/Mod/Assembly")
+
+# Switch to Kindred
+pref.SetString("Solver", "kindred")
+
+# Switch back to default
+pref.SetString("Solver", "")
+
+# Force the active assembly to pick up the change
+if hasattr(FreeCADGui, "ActiveDocument"):
+    for obj in FreeCAD.ActiveDocument.Objects:
+        if hasattr(obj, "resetSolver"):
+            obj.resetSolver()
+```
+
+## Interactive drag protocol
+
+The drag protocol provides real-time constraint solving during viewport part dragging. It is a three-phase protocol with a caching layer that avoids rebuilding the constraint system on every mouse move.
+
+### pre_drag(ctx, drag_parts)
+
+Called when the user begins dragging. Builds the constraint system once, runs the substitution pre-pass, constructs the symbolic Jacobian, compiles the evaluator, performs an initial solve, and caches everything in a `_DragCache` for reuse across subsequent `drag_step()` calls.
+
+```python
+def pre_drag(self, ctx, drag_parts):
+    self._drag_ctx = ctx
+    self._drag_parts = set(drag_parts)
+
+    system = _build_system(ctx)
+
+    half_spaces = compute_half_spaces(...)
+    weight_vec = build_weight_vector(system.params)
+
+    residuals = substitution_pass(system.all_residuals, system.params)
+    # single_equation_pass is intentionally skipped — it bakes variable
+    # values as constants that become stale when dragged parts move.
+
+    jac_exprs = [[r.diff(name).simplify() for name in free] for r in residuals]
+    compiled_eval = try_compile_system(residuals, jac_exprs, ...)
+
+    # Initial solve (Newton-Raphson + BFGS fallback)
+    newton_solve(residuals, system.params, ...)
+
+    # Cache for drag_step() reuse
+    cache = _DragCache()
+    cache.system = system
+    cache.residuals = residuals
+    cache.jac_exprs = jac_exprs
+    cache.compiled_eval = compiled_eval
+    cache.half_spaces = half_spaces
+    cache.weight_vec = weight_vec
+    ...
+    return result
+```
+
+**Important:** `single_equation_pass` is not used in the drag path. It analytically solves single-variable equations and bakes the results as `Const()` nodes into downstream expressions. During drag, those baked values become stale when part positions change, causing constraints to silently stop being enforced. Only `substitution_pass` (which replaces genuinely grounded parameters) is safe to cache.
+
+### drag_step(drag_placements)
+
+Called on each mouse move. Updates only the dragged part's 7 parameter values in the cached `ParamTable`, then re-solves using the cached residuals, Jacobian, and compiled evaluator. No system rebuild occurs.
+
+```python
+def drag_step(self, drag_placements):
+    cache = self._drag_cache
+    params = cache.system.params
+
+    # Update only the dragged part's parameters
+    for pr in drag_placements:
+        pfx = pr.id + "/"
+        params.set_value(pfx + "tx", pr.placement.position[0])
+        params.set_value(pfx + "ty", pr.placement.position[1])
+        params.set_value(pfx + "tz", pr.placement.position[2])
+        params.set_value(pfx + "qw", pr.placement.quaternion[0])
+        params.set_value(pfx + "qx", pr.placement.quaternion[1])
+        params.set_value(pfx + "qy", pr.placement.quaternion[2])
+        params.set_value(pfx + "qz", pr.placement.quaternion[3])
+
+    # Solve with cached artifacts — no rebuild
+    newton_solve(cache.residuals, params, ...,
+                 jac_exprs=cache.jac_exprs,
+                 compiled_eval=cache.compiled_eval)
+
+    return result
+```
+
+### post_drag()
+
+Called when the drag ends. Clears the cached state.
+
+```python
+def post_drag(self):
+    self._drag_ctx = None
+    self._drag_parts = None
+    self._drag_cache = None
+```
+
+### _DragCache
+
+The cache holds all artifacts built in `pre_drag()` that are invariant across drag steps (constraint topology doesn't change during a drag):
+
+| Field | Contents |
+|-------|----------|
+| `system` | `_System` -- owns `ParamTable` and `Expr` trees |
+| `residuals` | `list[Expr]` -- after substitution pass |
+| `jac_exprs` | `list[list[Expr]]` -- symbolic Jacobian |
+| `compiled_eval` | `Callable` or `None` -- native compiled evaluator |
+| `half_spaces` | `list[HalfSpace]` -- branch trackers |
+| `weight_vec` | `ndarray` or `None` -- minimum-movement weights |
+| `post_step_fn` | `Callable` or `None` -- half-space correction callback |
+
+### Performance
+
+The caching layer eliminates the expensive per-frame overhead (~150 ms for system build + Jacobian construction + compilation). Each `drag_step()` only evaluates the cached expressions at updated parameter values:
+
+- Newton-Raphson converges in 1-2 iterations from a nearby initial guess
+- The compiled evaluator (`codegen.py`) uses native Python `exec` for flat evaluation, avoiding the recursive tree-walk overhead
+- The substitution pass compiles grounded-body parameters to constants, reducing the effective system size
+- DOF counting is skipped during drag for speed (`result.dof = -1`)
+
+## Diagnostics integration
+
+`diagnose(ctx)` builds the constraint system and runs overconstrained detection, returning a list of `kcsolve.ConstraintDiagnostic` objects. The Assembly module calls this to populate the constraint diagnostics panel.
+
+```python
+def diagnose(self, ctx):
+    system = _build_system(ctx)
+    residuals = substitution_pass(system.all_residuals, system.params)
+    return _run_diagnostics(residuals, system.params, system.residual_ranges, ctx)
+```
+
+## Not yet implemented
+
+- **Kinematic simulation** (`run_kinematic`, `num_frames`, `update_for_frame`) -- the base class defaults return `Failed`. Requires time-stepping integration with motion driver expression evaluation.
+- **Joint limit enforcement** -- inequality constraints need active-set or barrier solver extensions.
+- **Fixed-joint bundling** (`supports_bundle_fixed()` returns `False`) -- the solver receives unbundled parts; the Assembly module pre-bundles when needed.
+- **Native export** (`export_native()`) -- no solver-native debug format defined.

docs/src/solver/constraints.md

@@ -0,0 +1,116 @@
+# Constraints
+
+Each constraint type maps to a class that produces residual expressions. The residuals equal zero when the constraint is satisfied. The number of residuals equals the number of degrees of freedom removed.
+
+**Source:** `mods/solver/kindred_solver/constraints.py`, `mods/solver/kindred_solver/geometry.py`
+
+## Constraint vocabulary
+
+### Point constraints
+
+| Type | DOF removed | Residuals |
+|------|-------------|-----------|
+| **Coincident** | 3 | `p_i - p_j` (world-frame marker origins coincide) |
+| **PointOnLine** | 2 | Two components of `(p_i - p_j) x z_j` (point lies on line through `p_j` along `z_j`) |
+| **PointInPlane** | 1 | `(p_i - p_j) . z_j - offset` (signed distance to plane) |
+
+### Orientation constraints
+
+| Type | DOF removed | Residuals |
+|------|-------------|-----------|
+| **Parallel** | 2 | Two components of `z_i x z_j` (cross product of Z-axes is zero) |
+| **Perpendicular** | 1 | `z_i . z_j` (dot product of Z-axes is zero) |
+| **Angle** | 1 | `z_i . z_j - cos(angle)` |
+
+### Axis/surface constraints
+
+| Type | DOF removed | Residuals |
+|------|-------------|-----------|
+| **Concentric** | 4 | Parallel Z-axes (2) + point-on-line (2) |
+| **Tangent** | 1 | `(p_i - p_j) . z_j` (signed distance along normal) |
+| **Planar** | 3 | Parallel normals (2) + point-in-plane (1) |
+| **LineInPlane** | 2 | Point-in-plane (1) + `z_i . n_j` (line direction perpendicular to normal) (1) |
+
+### Kinematic joints
+
+| Type | DOF removed | DOF remaining | Residuals |
+|------|-------------|---------------|-----------|
+| **Fixed** | 6 | 0 | Coincident origins (3) + quaternion error imaginary parts (3) |
+| **Ball** | 3 | 3 | Coincident origins (same as Coincident) |
+| **Revolute** | 5 | 1 (rotation about Z) | Coincident origins (3) + parallel Z-axes (2) |
+| **Cylindrical** | 4 | 2 (rotation + slide) | Parallel Z-axes (2) + point-on-line (2) |
+| **Slider** | 5 | 1 (slide along Z) | Parallel Z-axes (2) + point-on-line (2) + twist lock: `x_i . y_j` (1) |
+| **Screw** | 5 | 1 (helical) | Cylindrical (4) + pitch coupling: `axial - pitch * qz_rel / pi` (1) |
+| **Universal** | 4 | 2 (rotation about each Z) | Coincident origins (3) + perpendicular Z-axes (1) |
+
+### Mechanical elements
+
+| Type | DOF removed | Residuals |
+|------|-------------|-----------|
+| **Gear** | 1 | `r_i * qz_i + r_j * qz_j` (coupled rotation via quaternion Z-components) |
+| **RackPinion** | 1 | `translation - 2 * pitch_radius * qz_i` (rotation-translation coupling) |
+| **Cam** | 0 | Stub (no residuals) |
+| **Slot** | 0 | Stub (no residuals) |
+
+### Distance constraints
+
+| Type | DOF removed | Residuals |
+|------|-------------|-----------|
+| **DistancePointPoint** | 1 | `\|p_i - p_j\|^2 - d^2` (squared form avoids sqrt in Jacobian) |
+| **DistanceCylSph** | 0 | Stub (geometry classification dependent) |
+
+## Marker convention
+
+Every constraint references two parts (`body_i`, `body_j`) with local coordinate frames called markers. Each marker has a position (attachment point on the part) and a quaternion (orientation).
+
+The marker Z-axis defines the constraint direction:
+- **Revolute:** Z-axis = hinge axis
+- **Planar:** Z-axis = face normal
+- **PointOnLine:** Z-axis = line direction
+- **Slider:** Z-axis = slide direction
+
+The solver computes world-frame marker axes by composing the body quaternion with the marker quaternion: `q_world = q_body * q_marker`, then rotating unit vectors through the result.
+
+## Fixed constraint orientation
+
+The Fixed constraint locks all 6 DOF using a quaternion error formulation:
+
+1. Compute total orientation: `q_i = q_body_i * q_marker_i`, `q_j = q_body_j * q_marker_j`
+2. Compute relative quaternion: `q_err = conj(q_i) * q_j`
+3. When orientations match, `q_err` is the identity quaternion `(1, 0, 0, 0)`
+4. Residuals are the three imaginary components of `q_err` (should be zero)
+
+The quaternion normalization constraint on each body provides the fourth equation needed to fully determine the quaternion.
+
+## Rotation proxies for mechanical constraints
+
+Gear, RackPinion, and Screw constraints need to measure rotation angles. Rather than extracting Euler angles (which would introduce transcendentals), they use the Z-component of a relative quaternion as a proxy:
+
+```
+q_local = conj(q_marker) * q_body * q_marker
+angle ~ 2 * qz_local  (for small angles)
+```
+
+This is exact at the solution and has correct gradient direction, which is sufficient for Newton-Raphson convergence from a nearby initial guess.
+
+## Geometry helpers
+
+The `geometry.py` module provides Expr-level vector operations used by constraint classes:
+
+- `marker_z_axis(body, marker_quat)` -- world-frame Z-axis via `quat_rotate(q_body * q_marker, [0,0,1])`
+- `marker_x_axis(body, marker_quat)` -- world-frame X-axis (used by Slider twist lock)
+- `marker_y_axis(body, marker_quat)` -- world-frame Y-axis (used by Slider twist lock)
+- `dot3(a, b)` -- dot product of Expr triples
+- `cross3(a, b)` -- cross product of Expr triples
+- `point_plane_distance(point, origin, normal)` -- signed distance
+- `point_line_perp_components(point, origin, dir)` -- two perpendicular distance components
+
+## Writing a new constraint
+
+To add a constraint type:
+
+1. Subclass `ConstraintBase` in `constraints.py`
+2. Implement `residuals()` returning a list of `Expr` nodes
+3. Add a case in `solver.py:_build_constraint()` to instantiate it from `BaseJointKind`
+4. Add the `BaseJointKind` value to `_SUPPORTED` in `solver.py`
+5. Add the residual count to the tables in `decompose.py`

docs/src/solver/diagnostics.md

@@ -0,0 +1,117 @@
+# Diagnostics
+
+The solver provides three levels of constraint analysis: system-wide DOF counting, per-entity DOF decomposition, and overconstrained/conflicting constraint detection.
+
+## DOF counting
+
+**Source:** `mods/solver/kindred_solver/dof.py`
+
+Degrees of freedom are computed from the Jacobian rank:
+
+```
+DOF = n_free_params - rank(J)
+```
+
+Where `n_free_params` is the number of non-fixed parameters and `rank(J)` is the numerical rank of the Jacobian evaluated at current parameter values (SVD with tolerance `1e-8`).
+
+A well-constrained assembly has `DOF = 0` (exactly enough constraints to determine all positions). Positive DOF means underconstrained (parts can still move). Negative DOF is not possible with this formulation -- instead, rank deficiency in an overdetermined system indicates redundant constraints.
+
+The DOF value is reported in `SolveResult.dof` after every solve.
+
+## Per-entity DOF
+
+**Source:** `mods/solver/kindred_solver/diagnostics.py`
+
+`per_entity_dof()` breaks down the DOF count per body, identifying which motions remain free for each part:
+
+1. Build the full Jacobian
+2. For each non-grounded body, extract the 7 columns corresponding to its parameters
+3. Compute SVD of the sub-matrix; rank = number of constrained directions
+4. `remaining_dof = 7 - rank` (includes the quaternion normalization constraint counted in the rank)
+5. Classify null-space vectors as free motions by analyzing their translation vs. rotation components:
+   - Pure translation: >80% of the null vector's energy is in `tx, ty, tz` components
+   - Pure rotation: >80% of the energy is in `qw, qx, qy, qz` components
+   - Helical: mixed
+
+Returns a list of `EntityDOF` dataclasses:
+
+```python
+@dataclass
+class EntityDOF:
+    entity_id: str
+    remaining_dof: int
+    free_motions: list[str]  # e.g., ["rotation about Z", "translation along X"]
+```
+
+## Overconstrained detection
+
+**Source:** `mods/solver/kindred_solver/diagnostics.py`
+
+`find_overconstrained()` identifies redundant and conflicting constraints when the system is overconstrained (Jacobian is rank-deficient). It runs automatically when `solve()` fails to converge.
+
+### Algorithm
+
+Following the approach used by SolvSpace:
+
+1. **Check rank.** Build the full Jacobian `J`, compute its rank via SVD. If `rank == n_residuals`, the system is not overconstrained -- return empty.
+
+2. **Find redundant constraints.** For each constraint, temporarily remove its rows from J and re-check rank. If the rank is preserved, the constraint is **redundant** (removing it doesn't change the system's effective equations).
+
+3. **Distinguish conflicting from merely redundant.** Compute the left null space of J (columns of U beyond the rank). Project the residual vector onto this null space:
+   ```
+   null_residual = U_null^T @ r
+   residual_projection = U_null @ null_residual
+   ```
+   If a redundant constraint's residuals have significant projection onto the null space, it is **conflicting** -- it's both redundant and unsatisfied, meaning it contradicts other constraints.
+
+### Diagnostic output
+
+Returns `ConstraintDiag` dataclasses:
+
+```python
+@dataclass
+class ConstraintDiag:
+    constraint_index: int
+    kind: str           # "redundant" or "conflicting"
+    detail: str         # Human-readable explanation
+```
+
+These are converted to `kcsolve.ConstraintDiagnostic` objects in the IKCSolver bridge:
+
+| ConstraintDiag.kind | kcsolve.DiagnosticKind |
+|---------------------|----------------------|
+| `"redundant"` | `Redundant` |
+| `"conflicting"` | `Conflicting` |
+
+### Example
+
+Two Fixed joints between the same pair of parts:
+
+- Joint A: 6 residuals (3 position + 3 orientation)
+- Joint B: 6 residuals (same as Joint A)
+
+Jacobian rank = 6 (Joint B's rows are linearly dependent on Joint A's). Both joints are detected as redundant. If the joints specify different relative positions, both are also flagged as conflicting.
+
+## Solution preferences
+
+**Source:** `mods/solver/kindred_solver/preference.py`
+
+Solution preferences guide the solver toward physically intuitive solutions when multiple valid configurations exist.
+
+### Minimum-movement weighting
+
+The weight vector scales the Newton step to prefer solutions near the initial configuration. Translation parameters get weight `1.0`, quaternion parameters get weight `(180/pi)^2 ~ 3283`. This makes a 1-radian rotation equally "expensive" as a ~57-unit translation.
+
+The weighted minimum-norm step is:
+
+```
+J_scaled = J @ diag(W^{-1/2})
+dx_scaled = lstsq(J_scaled, -r)
+dx = dx_scaled * W^{-1/2}
+```
+
+This produces the minimum-norm solution in the weighted parameter space, biasing toward small movements.
+
+### Half-space tracking
+
+Described in detail in [Solving Algorithms: Half-space tracking](solving.md#half-space-tracking). Preserves the initial configuration's "branch" for constraints with multiple valid solutions by detecting and correcting branch crossings during iteration.

docs/src/solver/expression-dag.md

@@ -0,0 +1,96 @@
+# Expression DAG
+
+The expression DAG is the foundation of the Kindred solver. All constraint equations, Jacobian entries, and residuals are built as immutable trees of `Expr` nodes. This lets the solver compute exact symbolic derivatives and simplify constant sub-expressions before the iterative solve loop.
+
+**Source:** `mods/solver/kindred_solver/expr.py`
+
+## Node types
+
+Every node is a subclass of `Expr` and implements three methods:
+
+- `eval(env)` -- evaluate the expression given a name-to-value dictionary
+- `diff(var)` -- return a new Expr tree for the partial derivative with respect to `var`
+- `simplify()` -- return an algebraically simplified copy
+
+### Leaf nodes
+
+| Node | Description | diff(x) |
+|------|-------------|---------|
+| `Const(v)` | Literal floating-point value | 0 |
+| `Var(name)` | Named parameter (from `ParamTable`) | 1 if name matches, else 0 |
+
+### Unary nodes
+
+| Node | Description | diff(x) |
+|------|-------------|---------|
+| `Neg(f)` | Negation: `-f` | `-f'` |
+| `Sin(f)` | Sine: `sin(f)` | `cos(f) * f'` |
+| `Cos(f)` | Cosine: `cos(f)` | `-sin(f) * f'` |
+| `Sqrt(f)` | Square root: `sqrt(f)` | `f' / (2 * sqrt(f))` |
+
+### Binary nodes
+
+| Node | Description | diff(x) |
+|------|-------------|---------|
+| `Add(a, b)` | Sum: `a + b` | `a' + b'` |
+| `Sub(a, b)` | Difference: `a - b` | `a' - b'` |
+| `Mul(a, b)` | Product: `a * b` | `a'b + ab'` (product rule) |
+| `Div(a, b)` | Quotient: `a / b` | `(a'b - ab') / b^2` (quotient rule) |
+| `Pow(a, n)` | Power: `a^n` (constant exponent only) | `n * a^(n-1) * a'` |
+
+### Sentinels
+
+`ZERO = Const(0.0)` and `ONE = Const(1.0)` are pre-allocated constants used by `diff()` to avoid allocating trivial nodes.
+
+## Operator overloading
+
+Python's arithmetic operators are overloaded on `Expr`, so constraints can be written in natural notation:
+
+```python
+from kindred_solver.expr import Var, Const
+
+x = Var("x")
+y = Var("y")
+
+# Build the expression: x^2 + 2*x*y - 1
+expr = x**2 + 2*x*y - Const(1.0)
+
+# Evaluate at x=3, y=4
+expr.eval({"x": 3.0, "y": 4.0})  # 32.0
+
+# Symbolic derivative w.r.t. x
+dx = expr.diff("x").simplify()  # 2*x + 2*y
+dx.eval({"x": 3.0, "y": 4.0})   # 14.0
+```
+
+The `_wrap()` helper coerces plain `int` and `float` values to `Const` nodes automatically, so `2 * x` works without wrapping the `2`.
+
+## Simplification
+
+`simplify()` applies algebraic identities bottom-up:
+
+- Constant folding: `Const(2) + Const(3)` becomes `Const(5)`
+- Identity elimination: `x + 0 = x`, `x * 1 = x`, `x^0 = 1`, `x^1 = x`
+- Zero propagation: `0 * x = 0`
+- Negation collapse: `-(-x) = x`
+- Power expansion: `x^2` becomes `x * x` (avoids `pow()` in evaluation)
+
+Simplification is applied once to each Jacobian entry after symbolic differentiation, before the solve loop begins. This reduces the expression tree size and speeds up repeated evaluation.
+
+## How the solver uses expressions
+
+1. **Parameter registration.** `ParamTable.add("Part001/tx", 10.0)` creates a `Var("Part001/tx")` node and records its current value.
+
+2. **Constraint building.** Constraint classes compose `Var` nodes with arithmetic to produce residual `Expr` trees. For example, `CoincidentConstraint` builds `body_i.world_point() - body_j.world_point()`, producing 3 residual expressions.
+
+3. **Jacobian construction.** Newton-Raphson calls `r.diff(name).simplify()` for every (residual, free parameter) pair to build the symbolic Jacobian. This happens once before the solve loop.
+
+4. **Evaluation.** Each Newton iteration calls `expr.eval(env)` on every residual and Jacobian entry using the current parameter snapshot. `eval()` is a simple recursive tree walk with dictionary lookups.
+
+## Design notes
+
+**Why not numpy directly?** Symbolic expressions give exact derivatives without finite-difference approximations, and enable pre-passes (substitution, single-equation solve) that can eliminate variables before the iterative solver runs. The overhead of tree evaluation is acceptable for the problem sizes encountered in assembly solving (typically tens to hundreds of variables).
+
+**Why immutable?** Immutability means `diff()` can safely share sub-tree references between the original and derivative expressions. It also simplifies the substitution pass, which rebuilds trees with `Const` nodes replacing fixed `Var` nodes.
+
+**Limitations.** `Pow` differentiation only supports constant exponents. Variable exponents would require logarithmic differentiation (`d/dx f^g = f^g * (g' * ln(f) + g * f'/f)`), which hasn't been needed for assembly constraints.

docs/src/solver/overview.md

@@ -0,0 +1,92 @@
+# Kindred Solver Overview
+
+The Kindred solver is an expression-based Newton-Raphson constraint solver for the Assembly workbench. It is a pure-Python implementation that registers as a pluggable backend through the [KCSolve framework](../architecture/ondsel-solver.md), providing an alternative to the built-in OndselSolver (Lagrangian) backend.
+
+## Architecture
+
+```
+                            Assembly Module
+                                  │
+                      ┌───────────┴───────────┐
+                      │    SolverRegistry      │
+                      │  get("kindred")        │
+                      └───────────┬───────────┘
+                                  │
+                      ┌───────────┴───────────┐
+                      │    KindredSolver       │
+                      │  (kcsolve.IKCSolver)   │
+                      └───────────┬───────────┘
+                                  │
+              ┌───────────────────┼───────────────────┐
+              │                   │                   │
+     ┌────────┴────────┐  ┌──────┴──────┐  ┌────────┴────────┐
+     │  _build_system  │  │  Solve      │  │  Diagnostics    │
+     │  ────────────── │  │  ─────      │  │  ───────────    │
+     │  ParamTable     │  │  pre-passes │  │  DOF counting   │
+     │  RigidBody      │  │  Newton-R   │  │  overconstrained│
+     │  Constraints    │  │  BFGS       │  │  per-entity DOF │
+     │  Residuals      │  │  decompose  │  │  half-spaces    │
+     └─────────────────┘  └─────────────┘  └─────────────────┘
+```
+
+## Design principles
+
+**Symbolic differentiation.** All constraint equations are built as immutable expression DAGs (`Expr` trees). The Jacobian is computed symbolically via `expr.diff()` rather than finite differences. This gives exact derivatives, avoids numerical step-size tuning, and allows pre-passes to simplify or eliminate trivial equations before the iterative solver runs.
+
+**Residual-based formulation.** Each constraint produces a list of residual expressions that should evaluate to zero when satisfied. A Coincident constraint produces 3 residuals (dx, dy, dz), a Revolute produces 5 (3 position + 2 axis alignment), and so on. The solver minimizes the residual vector norm.
+
+**Unit quaternions for rotation.** Orientation is parameterized as a unit quaternion (w, x, y, z) rather than Euler angles, avoiding gimbal lock. A quaternion normalization residual (qw^2 + qx^2 + qy^2 + qz^2 - 1 = 0) is added for each free body, and quaternions are re-projected onto the unit sphere after each Newton step.
+
+**Current placements as initial guess.** The solver uses the parts' current positions as the initial guess, so it naturally converges to the nearest solution. Combined with half-space tracking, this produces physically intuitive results without branch-switching surprises.
+
+## Solve pipeline
+
+When `KindredSolver.solve(ctx)` is called with a `SolveContext`:
+
+1. **Build system** (`_build_system`) -- Create a `ParamTable` with 7 parameters per part (tx, ty, tz, qw, qx, qy, qz). Grounded parts have all parameters fixed. Build constraint objects from the context, collect their residual expressions, and add quaternion normalization residuals for free bodies.
+
+2. **Solution preferences** -- Compute half-space trackers for branching constraints (Distance, Parallel, Angle, Perpendicular) and build a minimum-movement weight vector that penalizes quaternion changes more than translation changes.
+
+3. **Pre-passes** -- Run the substitution pass (replace fixed parameters with constants) and the single-equation pass (analytically solve residuals with only one free variable).
+
+4. **Solve** -- For assemblies with 8+ free bodies, decompose the constraint graph into biconnected components and solve each cluster independently. For smaller assemblies, solve the full system monolithically. In both cases, use Newton-Raphson first, falling back to L-BFGS-B if Newton doesn't converge.
+
+5. **Post-process** -- Count degrees of freedom via Jacobian SVD rank. On failure, run overconstrained detection to identify redundant or conflicting constraints. Extract solved placements from the parameter table.
+
+## Module map
+
+| Module | Purpose |
+|--------|---------|
+| `solver.py` | `KindredSolver` class: IKCSolver bridge, solve/diagnose/drag entry points |
+| `expr.py` | Immutable expression DAG with eval, diff, simplify |
+| `params.py` | Parameter table: named variables with fixed/free tracking |
+| `entities.py` | `RigidBody`: 7-DOF entity owning solver parameters |
+| `quat.py` | Quaternion rotation as polynomial Expr trees |
+| `geometry.py` | Marker axis extraction, vector ops (dot, cross, point-plane, point-line) |
+| `constraints.py` | 24 constraint classes producing residual expressions |
+| `newton.py` | Newton-Raphson with symbolic Jacobian, quaternion renormalization |
+| `bfgs.py` | L-BFGS-B fallback via scipy |
+| `prepass.py` | Substitution pass and single-equation analytical solve |
+| `decompose.py` | Biconnected component graph decomposition and cluster-by-cluster solving |
+| `dof.py` | DOF counting via Jacobian SVD rank |
+| `diagnostics.py` | Overconstrained detection, per-entity DOF classification |
+| `preference.py` | Half-space tracking and minimum-movement weighting |
+
+## File locations
+
+- **Solver addon:** `mods/solver/` (git submodule)
+- **KCSolve C++ framework:** `src/Mod/Assembly/Solver/`
+- **Python bindings:** `src/Mod/Assembly/Solver/bindings/`
+- **Integration tests:** `src/Mod/Assembly/AssemblyTests/TestKindredSolverIntegration.py`
+- **Unit tests:** `mods/solver/tests/`
+
+## Related
+
+- [Expression DAG](expression-dag.md) -- the Expr type system
+- [Constraints](constraints.md) -- constraint vocabulary and residuals
+- [Solving algorithms](solving.md) -- Newton-Raphson, BFGS, decomposition
+- [Diagnostics](diagnostics.md) -- DOF counting, overconstrained detection
+- [Assembly integration](assembly-integration.md) -- IKCSolver bridge, preferences, drag
+- [Writing a custom solver](writing-a-solver.md) -- tutorial
+- [KCSolve architecture](../architecture/ondsel-solver.md) -- pluggable solver framework
+- [KCSolve Python API](../reference/kcsolve-python.md) -- kcsolve module reference

docs/src/solver/solving.md

@@ -0,0 +1,128 @@
+# Solving Algorithms
+
+The Kindred solver uses a multi-stage pipeline: pre-passes reduce the system, Newton-Raphson iterates toward a solution, and L-BFGS-B provides a fallback. For large assemblies, graph decomposition splits the system into independent clusters solved in sequence.
+
+## Pre-passes
+
+**Source:** `mods/solver/kindred_solver/prepass.py`
+
+Pre-passes run before the iterative solver and can eliminate variables analytically, reducing the problem size and improving convergence.
+
+### Substitution pass
+
+Replaces all fixed-parameter `Var` nodes with `Const` nodes carrying their current values, then simplifies. This compiles grounded-body parameters and previously-solved variables out of the expression trees.
+
+After substitution, residuals involving only fixed parameters simplify to constants (typically zero), and Jacobian entries for those parameters become exactly zero. This reduces the effective system size without changing the linear algebra.
+
+### Single-equation pass
+
+Scans residuals for any that depend on exactly one free variable. If the residual is linear in that variable (`a*x + b = 0`), it solves `x = -b/a` analytically, fixes the variable, and re-substitutes.
+
+The pass repeats until no more single-variable residuals can be solved. This handles cascading dependencies: solving one variable may reduce another residual to single-variable form.
+
+## Newton-Raphson
+
+**Source:** `mods/solver/kindred_solver/newton.py`
+
+The primary iterative solver. Each iteration:
+
+1. Evaluate the residual vector `r` and check convergence (`||r|| < tol`)
+2. Evaluate the Jacobian matrix `J` by calling `expr.eval()` on pre-computed symbolic derivatives
+3. Solve `J @ dx = -r` via `numpy.linalg.lstsq` (handles rank-deficient systems)
+4. Update parameters: `x += dx`
+5. Apply half-space correction (if configured)
+6. Re-normalize quaternions to unit length
+
+### Symbolic Jacobian
+
+The Jacobian is built once before the solve loop by calling `r.diff(name).simplify()` for every (residual, free parameter) pair. The resulting `Expr` trees are stored and re-evaluated at the current parameter values each iteration. This gives exact derivatives with no step-size tuning.
+
+### Weighted minimum-norm
+
+When a weight vector is provided, the step is column-scaled to produce the weighted minimum-norm solution. The solver scales J by W^{-1/2}, solves the scaled system, then unscales the step. This biases the solver toward solutions requiring smaller parameter changes in high-weight dimensions.
+
+The default weight vector assigns `1.0` to translation parameters and `~3283` to quaternion parameters (the square of 180/pi), making a 1-radian rotation equivalent to a ~57-unit translation. This produces physically intuitive solutions that prefer translating over rotating.
+
+### Quaternion renormalization
+
+After each Newton step, quaternion parameter groups `(qw, qx, qy, qz)` are re-projected onto the unit sphere by dividing by their norm. This prevents the quaternion from drifting away from unit length during iteration (the quaternion normalization residual only enforces this at convergence, not during intermediate steps).
+
+If a quaternion degenerates to near-zero norm, it is reset to the identity quaternion `(1, 0, 0, 0)`.
+
+### Convergence
+
+Newton-Raphson runs for up to 100 iterations with tolerance `1e-10` on the residual norm. For well-conditioned systems near the solution, convergence is typically quadratic (3-5 iterations). Interactive drag from a nearby position typically converges in 1-2 iterations.
+
+## L-BFGS-B fallback
+
+**Source:** `mods/solver/kindred_solver/bfgs.py`
+
+If Newton-Raphson fails to converge, L-BFGS-B minimizes the sum of squared residuals: `f(x) = 0.5 * sum(r_i^2)`. This is a quasi-Newton method that approximates the Hessian from gradient history, with bounded memory usage.
+
+The gradient is computed analytically from the same symbolic Jacobian: `grad = J^T @ r`. This is passed directly to `scipy.optimize.minimize` via the `jac=True` interface to avoid redundant function evaluations.
+
+L-BFGS-B is more robust for ill-conditioned systems where the Jacobian is nearly singular, but converges more slowly (superlinear rather than quadratic). It runs for up to 200 iterations.
+
+If scipy is not available, the fallback is skipped gracefully.
+
+## Graph decomposition
+
+**Source:** `mods/solver/kindred_solver/decompose.py`
+
+For assemblies with 8 or more free bodies, the solver decomposes the constraint graph into clusters and solves them independently. This improves performance for large assemblies by reducing the Jacobian size from O(n^2) to the sum of smaller cluster Jacobians.
+
+### Algorithm
+
+1. **Build constraint graph.** Bodies are nodes, constraints are edges weighted by their residual count (DOF removed). Grounded bodies are tagged.
+
+2. **Find biconnected components.** Using `networkx.biconnected_components()`, decompose the graph into rigid clusters. Articulation points (bodies shared between clusters) are identified.
+
+3. **Build block-cut tree.** A bipartite graph of clusters and articulation points, rooted at a grounded cluster.
+
+4. **BFS ordering.** Traverse the block-cut tree root-to-leaf, producing a solve order where grounded clusters come first and boundary conditions propagate outward.
+
+5. **Solve each cluster.** For each cluster in order:
+   - Fix boundary bodies that were already solved by previous clusters (their parameters become constants)
+   - Collect the cluster's residuals and quaternion normalization equations
+   - Run substitution pass (compiles fixed boundary values to constants)
+   - Newton-Raphson + BFGS fallback on the reduced system
+   - Mark the cluster's bodies as solved
+   - Unfix boundary parameters for downstream clusters
+
+### Example
+
+Consider a chain of 4 bodies: `Ground -- A -- B -- C` with joints at each connection. This decomposes into two biconnected components (if the joints create articulation points):
+
+- Cluster 1: {Ground, A} -- solved first (grounded)
+- Cluster 2: {A, B, C} -- solved second with A's parameters fixed to Cluster 1's result
+
+The 21-variable monolithic system (3 free bodies x 7 params) becomes two smaller systems solved in sequence.
+
+### Disconnected sub-assemblies
+
+The decomposition also handles disconnected components. Each connected component of the constraint graph is decomposed independently. Components without a grounded body will fail to solve (returning `NoGroundedParts`).
+
+### Pebble game integration
+
+The `classify_cluster_rigidity()` function uses the pebble game algorithm from `GNN/solver/datagen/` to classify clusters as well-constrained, underconstrained, overconstrained, or mixed. This provides fast O(n) rigidity analysis without running the full solver.
+
+## Half-space tracking
+
+**Source:** `mods/solver/kindred_solver/preference.py`
+
+Many constraints have multiple valid solutions (branches). A distance constraint between two points can be satisfied with the points on either side of each other. Parallel axes can point in the same or opposite directions.
+
+Half-space tracking preserves the initial configuration branch:
+
+1. **At setup:** Evaluate an indicator function for each branching constraint. Record its sign as the reference branch.
+
+2. **After each Newton step:** Re-evaluate the indicator. If the sign flipped, apply a correction to push the solution back to the reference branch.
+
+Tracked constraint types:
+
+| Constraint | Indicator | Correction |
+|-----------|-----------|------------|
+| DistancePointPoint (d > 0) | Dot product of displacement with reference direction | Reflect the moving body's position |
+| Parallel | `z_i . z_j` (same vs. opposite direction) | None (tracked for monitoring) |
+| Angle | Dominant cross product component | None (tracked for monitoring) |
+| Perpendicular | Dominant cross product component | None (tracked for monitoring) |

docs/src/solver/writing-a-solver.md

@@ -0,0 +1,256 @@
+# Writing a Custom Solver
+
+The KCSolve framework lets you implement a solver backend in pure Python, register it at runtime, and select it through the Assembly preferences. This tutorial walks through building a minimal solver and then extending it.
+
+## Minimal solver
+
+A solver must subclass `kcsolve.IKCSolver` and implement three methods:
+
+```python
+import kcsolve
+
+class MySolver(kcsolve.IKCSolver):
+    def __init__(self):
+        super().__init__()  # required for pybind11 trampoline
+
+    def name(self):
+        return "My Custom Solver"
+
+    def supported_joints(self):
+        return [
+            kcsolve.BaseJointKind.Fixed,
+            kcsolve.BaseJointKind.Revolute,
+        ]
+
+    def solve(self, ctx):
+        result = kcsolve.SolveResult()
+
+        # Find grounded parts
+        grounded = {p.id for p in ctx.parts if p.grounded}
+        if not grounded:
+            result.status = kcsolve.SolveStatus.NoGroundedParts
+            return result
+
+        # Your solving logic here...
+        # For each non-grounded part, compute its solved placement
+        for part in ctx.parts:
+            if part.grounded:
+                continue
+            pr = kcsolve.SolveResult.PartResult()
+            pr.id = part.id
+            pr.placement = part.placement  # use current placement as placeholder
+            result.placements = result.placements + [pr]
+
+        result.status = kcsolve.SolveStatus.Success
+        result.dof = 0
+        return result
+```
+
+Register it:
+
+```python
+kcsolve.register_solver("my_solver", MySolver)
+```
+
+Test it from the FreeCAD console:
+
+```python
+solver = kcsolve.load("my_solver")
+print(solver.name())  # "My Custom Solver"
+
+ctx = kcsolve.SolveContext()
+# ... build context ...
+result = solver.solve(ctx)
+print(result.status)  # SolveStatus.Success
+```
+
+## Addon packaging
+
+To make your solver load automatically, create a FreeCAD addon:
+
+```
+my_solver_addon/
+  package.xml          # Addon manifest
+  Init.py              # Registration entry point
+  my_solver/
+    __init__.py
+    solver.py          # MySolver class
+```
+
+**package.xml:**
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<package format="1">
+  <name>MyCustomSolver</name>
+  <description>Custom assembly constraint solver</description>
+  <version>0.1.0</version>
+  <content>
+    <preferencepack>
+      <name>MySolver</name>
+    </preferencepack>
+  </content>
+</package>
+```
+
+**Init.py:**
+```python
+import kcsolve
+from my_solver.solver import MySolver
+kcsolve.register_solver("my_solver", MySolver)
+```
+
+Place the addon in the FreeCAD Mod directory or as a git submodule in `mods/`.
+
+## Working with SolveContext
+
+The `SolveContext` contains everything the solver needs:
+
+### Parts
+
+```python
+for part in ctx.parts:
+    print(f"{part.id}: grounded={part.grounded}")
+    print(f"  position: {list(part.placement.position)}")
+    print(f"  quaternion: {list(part.placement.quaternion)}")
+    print(f"  mass: {part.mass}")
+```
+
+Each part has 7 degrees of freedom: 3 translation (x, y, z) and 4 quaternion components (w, x, y, z) with a unit-norm constraint reducing the rotational DOF to 3.
+
+**Quaternion convention:** `(w, x, y, z)` where `w` is the scalar part. This differs from FreeCAD's `Base.Rotation(x, y, z, w)`. The adapter layer handles the swap.
+
+### Constraints
+
+```python
+for c in ctx.constraints:
+    if not c.activated:
+        continue
+    print(f"{c.id}: {c.type} between {c.part_i} and {c.part_j}")
+    print(f"  marker_i: pos={list(c.marker_i.position)}, "
+          f"quat={list(c.marker_i.quaternion)}")
+    print(f"  params: {list(c.params)}")
+    print(f"  limits: {len(c.limits)}")
+```
+
+The marker transforms define local coordinate frames on each part. The constraint type determines what geometric relationship is enforced between these frames.
+
+### Returning results
+
+```python
+result = kcsolve.SolveResult()
+result.status = kcsolve.SolveStatus.Success
+result.dof = computed_dof
+
+placements = []
+for part_id, pos, quat in solved_parts:
+    pr = kcsolve.SolveResult.PartResult()
+    pr.id = part_id
+    pr.placement = kcsolve.Transform()
+    pr.placement.position = list(pos)
+    pr.placement.quaternion = list(quat)
+    placements.append(pr)
+result.placements = placements
+
+return result
+```
+
+**Important:** pybind11 list fields return copies. Use `result.placements = [...]` (whole-list assignment), not `result.placements.append(...)`.
+
+## Adding optional capabilities
+
+### Diagnostics
+
+Override `diagnose()` to detect overconstrained or malformed assemblies:
+
+```python
+def diagnose(self, ctx):
+    diagnostics = []
+    # ... analyze constraints ...
+    d = kcsolve.ConstraintDiagnostic()
+    d.constraint_id = "Joint001"
+    d.kind = kcsolve.DiagnosticKind.Redundant
+    d.detail = "This joint duplicates Joint002"
+    diagnostics.append(d)
+    return diagnostics
+```
+
+### Interactive drag
+
+Override the three drag methods for real-time viewport dragging:
+
+```python
+def pre_drag(self, ctx, drag_parts):
+    self._ctx = ctx
+    self._dragging = set(drag_parts)
+    return self.solve(ctx)
+
+def drag_step(self, drag_placements):
+    # Update dragged parts in stored context
+    for pr in drag_placements:
+        for part in self._ctx.parts:
+            if part.id == pr.id:
+                part.placement = pr.placement
+                break
+    return self.solve(self._ctx)
+
+def post_drag(self):
+    self._ctx = None
+    self._dragging = None
+```
+
+For responsive dragging, the solver should converge quickly from a nearby initial guess. Use warm-starting (current placements as initial guess) and consider caching internal state across drag steps.
+
+### Incremental update
+
+Override `update()` for the case where only constraint parameters changed (not topology):
+
+```python
+def update(self, ctx):
+    # Reuse cached factorization, only re-evaluate changed residuals
+    return self.solve(ctx)  # default: just re-solve
+```
+
+## Testing
+
+### Unit tests (without FreeCAD)
+
+Test your solver logic with hand-built `SolveContext` objects:
+
+```python
+import kcsolve
+
+def test_fixed_joint():
+    ctx = kcsolve.SolveContext()
+
+    base = kcsolve.Part()
+    base.id = "base"
+    base.grounded = True
+
+    arm = kcsolve.Part()
+    arm.id = "arm"
+    arm.placement.position = [100.0, 0.0, 0.0]
+
+    joint = kcsolve.Constraint()
+    joint.id = "Joint001"
+    joint.part_i = "base"
+    joint.part_j = "arm"
+    joint.type = kcsolve.BaseJointKind.Fixed
+
+    ctx.parts = [base, arm]
+    ctx.constraints = [joint]
+
+    solver = MySolver()
+    result = solver.solve(ctx)
+    assert result.status == kcsolve.SolveStatus.Success
+```
+
+### Integration tests (with FreeCAD)
+
+For integration testing within FreeCAD, follow the pattern in `TestKindredSolverIntegration.py`: set the solver preference in `setUp()`, create document objects, and verify solve results.
+
+## Reference
+
+- [KCSolve Python API](../reference/kcsolve-python.md) -- complete type and function reference
+- [KCSolve Architecture](../architecture/ondsel-solver.md) -- C++ framework details
+- [Constraints](constraints.md) -- constraint types and residual counts
+- [Kindred Solver Overview](overview.md) -- how the built-in Kindred solver works

package/debian/build-deb.sh

@@ -30,7 +30,7 @@ fi
 
 # Get version from git if not provided
 if [ -z "$VERSION" ]; then
-    VERSION=$(cd "$PROJECT_ROOT" && git describe --tags --always 2>/dev/null || echo "0.1.0")
+    VERSION=$(cd "$PROJECT_ROOT" && git describe --tags --always 2>/dev/null || echo "0.1.5")
 fi
 
 # Convert version to Debian-compatible format

package/rattler-build/recipe.yaml

@@ -155,6 +155,7 @@ requirements:
     - lark
     - lxml
     - matplotlib-base
+    - networkx
     - nine
     - noqt5
     - numpy>=1.26,<2

src/Gui/Application.cpp

@@ -1046,6 +1046,9 @@ void Application::slotNewDocument(const App::Document& Doc, bool isMainDoc)
     );
     pDoc->signalInEdit.connect(std::bind(&Gui::Application::slotInEdit, this, sp::_1));
     pDoc->signalResetEdit.connect(std::bind(&Gui::Application::slotResetEdit, this, sp::_1));
+    pDoc->signalActivatedViewProvider.connect(
+        std::bind(&Gui::Application::slotActivatedViewProvider, this, sp::_1, sp::_2)
+    );
     // NOLINTEND
 
     signalNewDocument(*pDoc, isMainDoc);
@@ -1352,6 +1355,12 @@ void Application::slotResetEdit(const Gui::ViewProviderDocumentObject& vp)
     this->signalResetEdit(vp);
 }
 
+void Application::slotActivatedViewProvider(
+    const Gui::ViewProviderDocumentObject* vp, const char* name)
+{
+    this->signalActivatedViewProvider(vp, name);
+}
+
 void Application::onLastWindowClosed(Gui::Document* pcDoc)
 {
     try {

src/Gui/Application.h

@@ -153,6 +153,9 @@ public:
     fastsignals::signal<void(const Gui::ViewProviderDocumentObject&)> signalInEdit;
     /// signal on leaving edit mode
     fastsignals::signal<void(const Gui::ViewProviderDocumentObject&)> signalResetEdit;
+    /// signal on activated view-provider (active-object change, e.g. "pdbody", "part")
+    fastsignals::signal<void(const Gui::ViewProviderDocumentObject*, const char*)>
+        signalActivatedViewProvider;
     /// signal on changing user edit mode
     fastsignals::signal<void(int)> signalUserEditModeChanged;
     //@}
@@ -174,6 +177,7 @@ protected:
     void slotActivatedObject(const ViewProvider&);
     void slotInEdit(const Gui::ViewProviderDocumentObject&);
     void slotResetEdit(const Gui::ViewProviderDocumentObject&);
+    void slotActivatedViewProvider(const Gui::ViewProviderDocumentObject*, const char*);
 
 public:
     /// message when a GuiDocument is about to vanish

src/Gui/EditingContext.cpp

@@ -121,6 +121,9 @@ EditingContextResolver::EditingContextResolver()
     app.signalActiveDocument.connect([this](const Document& doc) { onActiveDocument(doc); });
     app.signalActivateView.connect([this](const MDIView* view) { onActivateView(view); });
     app.signalActivateWorkbench.connect([this](const char*) { refresh(); });
+    app.signalActivatedViewProvider.connect(
+        [this](const ViewProviderDocumentObject*, const char*) { refresh(); }
+    );
 }
 
 EditingContextResolver::~EditingContextResolver()
@@ -172,6 +175,23 @@ static App::DocumentObject* getActivePartObject()
     return view->getActiveObject<App::DocumentObject*>("part");
 }
 
+// ---------------------------------------------------------------------------
+// Helper: get the active "pdbody" object from the active view
+// ---------------------------------------------------------------------------
+
+static App::DocumentObject* getActivePdBodyObject()
+{
+    auto* guiDoc = Application::Instance->activeDocument();
+    if (!guiDoc) {
+        return nullptr;
+    }
+    auto* view = guiDoc->getActiveView();
+    if (!view) {
+        return nullptr;
+    }
+    return view->getActiveObject<App::DocumentObject*>("pdbody");
+}
+
 // ---------------------------------------------------------------------------
 // Helper: get the label of the active "part" object
 // ---------------------------------------------------------------------------
@@ -213,6 +233,34 @@ static QString getInEditLabel()
 
 void EditingContextResolver::registerBuiltinContexts()
 {
+    // --- PartDesign body active inside an assembly (supersedes assembly.edit) ---
+    registerContext({
+        /*.id =*/QStringLiteral("partdesign.in_assembly"),
+        /*.labelTemplate =*/QStringLiteral("Body: {name}"),
+        /*.color =*/QLatin1String(CatppuccinMocha::Mauve),
+        /*.toolbars =*/
+        {QStringLiteral("Part Design Helper Features"),
+         QStringLiteral("Part Design Modeling Features"),
+         QStringLiteral("Part Design Dress-Up Features"),
+         QStringLiteral("Part Design Transformation Features"),
+         QStringLiteral("Sketcher")},
+        /*.priority =*/95,
+        /*.match =*/
+        []() {
+            auto* body = getActivePdBodyObject();
+            if (!body || !objectIsDerivedFrom(body, "PartDesign::Body")) {
+                return false;
+            }
+            // Only match when we're inside an assembly edit session
+            auto* doc = Application::Instance->activeDocument();
+            if (!doc) {
+                return false;
+            }
+            auto* vp = doc->getInEdit();
+            return vp && vpObjectIsDerivedFrom(vp, "Assembly::AssemblyObject");
+        },
+    });
+
     // --- Sketcher edit (highest priority — VP in edit) ---
     registerContext({
         /*.id =*/QStringLiteral("sketcher.edit"),
@@ -272,7 +320,10 @@ void EditingContextResolver::registerBuiltinContexts()
         /*.priority =*/40,
         /*.match =*/
         []() {
-            auto* obj = getActivePartObject();
+            auto* obj = getActivePdBodyObject();
+            if (!obj) {
+                obj = getActivePartObject();
+            }
             if (!obj || !objectIsDerivedFrom(obj, "PartDesign::Body")) {
                 return false;
             }
@@ -301,7 +352,10 @@ void EditingContextResolver::registerBuiltinContexts()
         /*.priority =*/30,
         /*.match =*/
         []() {
-            auto* obj = getActivePartObject();
+            auto* obj = getActivePdBodyObject();
+            if (!obj) {
+                obj = getActivePartObject();
+            }
             return obj && objectIsDerivedFrom(obj, "PartDesign::Body");
         },
     });
@@ -488,6 +542,13 @@ EditingContext EditingContextResolver::resolve() const
             if (label.contains(QStringLiteral("{name}"))) {
                 // For edit-mode contexts, use the in-edit object name
                 QString name = getInEditLabel();
+                if (name.isEmpty()) {
+                    // Try pdbody first for PartDesign contexts
+                    auto* bodyObj = getActivePdBodyObject();
+                    if (bodyObj) {
+                        name = QString::fromUtf8(bodyObj->Label.getValue());
+                    }
+                }
                 if (name.isEmpty()) {
                     name = getActivePartLabel();
                 }
@@ -548,6 +609,25 @@ QStringList EditingContextResolver::buildBreadcrumb(const EditingContext& ctx) c
         return crumbs;
     }
 
+    // Assembly > Body breadcrumb for in-assembly part editing
+    if (ctx.id == QStringLiteral("partdesign.in_assembly")) {
+        auto* guiDoc = Application::Instance->activeDocument();
+        if (guiDoc) {
+            auto* vp = guiDoc->getInEdit();
+            if (vp) {
+                auto* vpd = dynamic_cast<ViewProviderDocumentObject*>(vp);
+                if (vpd && vpd->getObject()) {
+                    crumbs << QString::fromUtf8(vpd->getObject()->Label.getValue());
+                }
+            }
+        }
+        auto* body = getActivePdBodyObject();
+        if (body) {
+            crumbs << QString::fromUtf8(body->Label.getValue());
+        }
+        return crumbs;
+    }
+
     // Always start with the active part/body/assembly label
     QString partLabel = getActivePartLabel();
     if (!partLabel.isEmpty()) {
@@ -582,6 +662,14 @@ QStringList EditingContextResolver::buildBreadcrumbColors(const EditingContext&
 {
     QStringList colors;
 
+    if (ctx.id == QStringLiteral("partdesign.in_assembly")) {
+        for (int i = 0; i < ctx.breadcrumb.size(); ++i) {
+            colors << (i == 0 ? QLatin1String(CatppuccinMocha::Blue)
+                              : QLatin1String(CatppuccinMocha::Mauve));
+        }
+        return colors;
+    }
+
     if (ctx.breadcrumb.size() <= 1) {
         colors << ctx.color;
         return colors;

src/Gui/Stylesheets/KindredCreate.qss

@@ -251,7 +251,6 @@ QDockWidget::title {
     text-align: left;
     padding: 8px 6px;
     border-bottom: 1px solid #313244;
-    min-height: 18px;
 }
 
 QDockWidget::close-button,
@@ -733,7 +732,7 @@ QGroupBox {
     background-color: #1e1e2e;
     border: 1px solid #45475a;
     border-radius: 6px;
-    margin-top: 12px;
+    margin-top: 16px;
     padding-top: 8px;
 }
 
@@ -741,7 +740,7 @@ QGroupBox::title {
     subcontrol-origin: margin;
     subcontrol-position: top left;
     left: 12px;
-    padding: 0 4px;
+    padding: 2px 4px;
     color: #bac2de;
     background-color: #1e1e2e;
 }
@@ -1234,7 +1233,7 @@ QSint--ActionGroup QToolButton {
     border: none;
     border-radius: 4px;
     padding: 8px 6px;
-    min-height: 18px;
+    min-height: 0px;
 }
 
 QSint--ActionGroup QToolButton:hover {

src/Mod/Assembly/App/AssemblyLink.cpp

@@ -311,6 +311,19 @@ void AssemblyLink::updateContents()
     purgeTouched();
 }
 
+// Generate an instance label for assembly components by appending a -N suffix.
+// All instances get a suffix (starting at -1) so that structured part numbers
+// like "P03-0001" are never mangled by UniqueNameManager's trailing-digit logic.
+static std::string makeInstanceLabel(App::Document* doc, const std::string& baseLabel)
+{
+    for (int i = 1;; ++i) {
+        std::string candidate = baseLabel + "-" + std::to_string(i);
+        if (!doc->containsLabel(candidate)) {
+            return candidate;
+        }
+    }
+}
+
 void AssemblyLink::synchronizeComponents()
 {
     App::Document* doc = getDocument();
@@ -428,7 +441,7 @@ void AssemblyLink::synchronizeComponents()
                 auto* subAsmLink = static_cast<AssemblyLink*>(newObj);
                 subAsmLink->LinkedObject.setValue(obj);
                 subAsmLink->Rigid.setValue(asmLink->Rigid.getValue());
-                subAsmLink->Label.setValue(obj->Label.getValue());
+                subAsmLink->Label.setValue(makeInstanceLabel(doc, obj->Label.getValue()));
                 addObject(subAsmLink);
                 link = subAsmLink;
             }
@@ -440,7 +453,7 @@ void AssemblyLink::synchronizeComponents()
                 );
                 newLink->LinkedObject.setValue(srcLink->getTrueLinkedObject(false));
 
-                newLink->Label.setValue(obj->Label.getValue());
+                newLink->Label.setValue(makeInstanceLabel(doc, obj->Label.getValue()));
                 addObject(newLink);
 
                 newLink->ElementCount.setValue(srcLink->ElementCount.getValue());
@@ -461,7 +474,7 @@ void AssemblyLink::synchronizeComponents()
                 App::DocumentObject* newObj = doc->addObject("App::Link", obj->getNameInDocument());
                 auto* newLink = static_cast<App::Link*>(newObj);
                 newLink->LinkedObject.setValue(obj);
-                newLink->Label.setValue(obj->Label.getValue());
+                newLink->Label.setValue(makeInstanceLabel(doc, obj->Label.getValue()));
                 addObject(newLink);
                 link = newLink;
             }

src/Mod/Assembly/App/AssemblyObject.cpp

@@ -30,6 +30,7 @@
 
 #include <App/Application.h>
 #include <App/Datums.h>
+#include <App/Origin.h>
 #include <App/Document.h>
 #include <App/DocumentObjectGroup.h>
 #include <App/FeaturePythonPyImp.h>
@@ -106,6 +107,24 @@ AssemblyObject::AssemblyObject()
 
 AssemblyObject::~AssemblyObject() = default;
 
+void AssemblyObject::setupObject()
+{
+    App::Part::setupObject();
+
+    // Relabel origin planes with assembly-friendly names (SolidWorks convention)
+    if (auto* origin = getOrigin()) {
+        if (auto* xy = origin->getXY()) {
+            xy->Label.setValue("Top");
+        }
+        if (auto* xz = origin->getXZ()) {
+            xz->Label.setValue("Front");
+        }
+        if (auto* yz = origin->getYZ()) {
+            yz->Label.setValue("Right");
+        }
+    }
+}
+
 PyObject* AssemblyObject::getPyObject()
 {
     if (PythonObject.is(Py::_None())) {
@@ -157,6 +176,10 @@ KCSolve::IKCSolver* AssemblyObject::getOrCreateSolver()
         std::string solverName = hGrp->GetASCII("Solver", "");
         solver_ = KCSolve::SolverRegistry::instance().get(solverName);
         // get("") returns the registry default (first registered solver)
+        if (solver_) {
+            FC_LOG("Assembly : loaded solver '" << solver_->name()
+                   << "' (requested='" << solverName << "')");
+        }
     }
     return solver_.get();
 }
@@ -193,14 +216,22 @@ int AssemblyObject::solve(bool enableRedo, bool updateJCS)
 
     auto groundedObjs = getGroundedParts();
     if (groundedObjs.empty()) {
+        FC_LOG("Assembly : solve skipped — no grounded parts");
         return -6;
     }
 
     std::vector<App::DocumentObject*> joints = getJoints(updateJCS);
     removeUnconnectedJoints(joints, groundedObjs);
 
+    FC_LOG("Assembly : solve on '" << getFullLabel()
+           << "' — " << groundedObjs.size() << " grounded, "
+           << joints.size() << " joints");
+
     KCSolve::SolveContext ctx = buildSolveContext(joints);
 
+    FC_LOG("Assembly : solve context — " << ctx.parts.size() << " parts, "
+           << ctx.constraints.size() << " constraints");
+
     // Always save placements to enable orientation flip detection
     savePlacementsForUndo();
 
@@ -222,6 +253,13 @@ int AssemblyObject::solve(bool enableRedo, bool updateJCS)
     }
 
     if (lastResult_.status == KCSolve::SolveStatus::Failed) {
+        FC_LOG("Assembly : solve failed — status="
+               << static_cast<int>(lastResult_.status)
+               << ", " << lastResult_.diagnostics.size() << " diagnostics");
+        for (const auto& d : lastResult_.diagnostics) {
+            Base::Console().warning("Assembly : diagnostic [%s]: %s\n",
+                                    d.constraint_id.c_str(), d.detail.c_str());
+        }
         updateSolveStatus();
         return -1;
     }
@@ -229,6 +267,7 @@ int AssemblyObject::solve(bool enableRedo, bool updateJCS)
     // Validate that the solve didn't cause any parts to flip orientation
     if (!validateNewPlacements()) {
         // Restore previous placements - the solve found an invalid configuration
+        FC_LOG("Assembly : solve rejected — placement validation failed, undoing");
         undoSolve();
         lastSolverStatus = -2;
         updateSolveStatus();
@@ -246,6 +285,9 @@ int AssemblyObject::solve(bool enableRedo, bool updateJCS)
 
     updateSolveStatus();
 
+    FC_LOG("Assembly : solve succeeded — dof=" << lastResult_.dof
+           << ", " << lastResult_.placements.size() << " placements");
+
     return 0;
 }
 
@@ -256,8 +298,14 @@ void AssemblyObject::updateSolveStatus()
     //+1 because there's a grounded joint to origin
     lastDoF = (1 + numberOfComponents()) * 6;
 
-    if (!solver_ || lastResult_.placements.empty()) {
+    // Guard against re-entrancy: solve() calls updateSolveStatus(), so if
+    // placements are legitimately empty (e.g. zero constraints / all parts
+    // grounded) the recursive solve() would never terminate.
+    static bool updating = false;
+    if (!updating && (!solver_ || lastResult_.placements.empty())) {
+        updating = true;
         solve();
+        updating = false;
     }
 
     if (!solver_) {
@@ -390,6 +438,8 @@ size_t Assembly::AssemblyObject::numberOfFrames()
 void AssemblyObject::preDrag(std::vector<App::DocumentObject*> dragParts)
 {
     bundleFixed = true;
+    dragStepCount_ = 0;
+    dragStepRejected_ = 0;
 
     auto* solver = getOrCreateSolver();
     if (!solver) {
@@ -402,6 +452,7 @@ void AssemblyObject::preDrag(std::vector<App::DocumentObject*> dragParts)
 
     auto groundedObjs = getGroundedParts();
     if (groundedObjs.empty()) {
+        FC_LOG("Assembly : preDrag skipped — no grounded parts");
         bundleFixed = false;
         return;
     }
@@ -455,6 +506,10 @@ void AssemblyObject::preDrag(std::vector<App::DocumentObject*> dragParts)
         }
     }
 
+    FC_LOG("Assembly : preDrag — " << dragPartIds.size() << " drag part(s), "
+           << joints.size() << " joints, " << ctx.parts.size() << " parts, "
+           << ctx.constraints.size() << " constraints");
+
     savePlacementsForUndo();
 
     try {
@@ -463,11 +518,13 @@ void AssemblyObject::preDrag(std::vector<App::DocumentObject*> dragParts)
     }
     catch (...) {
         // If pre_drag fails, we still need to be in a valid state
+        FC_LOG("Assembly : preDrag — solver pre_drag threw exception");
     }
 }
 
 void AssemblyObject::doDragStep()
 {
+    dragStepCount_++;
     try {
         std::vector<KCSolve::SolveResult::PartResult> dragPlacements;
 
@@ -487,9 +544,21 @@ void AssemblyObject::doDragStep()
 
         lastResult_ = solver_->drag_step(dragPlacements);
 
+        if (lastResult_.status == KCSolve::SolveStatus::Failed) {
+            FC_LOG("Assembly : dragStep #" << dragStepCount_ << " — solver failed");
+        }
+
         if (validateNewPlacements()) {
             setNewPlacements();
 
+            // Update the baseline positions after each accepted drag step so that
+            // the orientation-flip check in validateNewPlacements() compares against
+            // the last accepted state rather than the pre-drag origin.  Without this,
+            // cumulative rotation during a long drag easily exceeds the 91-degree
+            // threshold and causes the solver result to be rejected ("flipped
+            // orientation"), making parts appear to explode.
+            savePlacementsForUndo();
+
             auto joints = getJoints(false);
             for (auto* joint : joints) {
                 if (joint->Visibility.getValue()) {
@@ -498,9 +567,12 @@ void AssemblyObject::doDragStep()
                 }
             }
         }
+        else {
+            dragStepRejected_++;
+        }
     }
     catch (...) {
-        // We do nothing if a solve step fails.
+        FC_LOG("Assembly : dragStep #" << dragStepCount_ << " — exception");
     }
 }
 
@@ -612,6 +684,8 @@ bool AssemblyObject::validateNewPlacements()
 
 void AssemblyObject::postDrag()
 {
+    FC_LOG("Assembly : postDrag — " << dragStepCount_ << " steps, "
+           << dragStepRejected_ << " rejected");
     if (solver_) {
         solver_->post_drag();
     }
@@ -1041,10 +1115,19 @@ KCSolve::SolveContext AssemblyObject::buildSolveContext(
                         break;
 
                     default:
+                        FC_WARN("Assembly : Distance joint '" << joint->getFullName()
+                                << "' — unhandled DistanceType "
+                                << distanceTypeName(distType)
+                                << ", falling back to Planar");
                         kind = KCSolve::BaseJointKind::Planar;
                         params.push_back(distance);
                         break;
                 }
+
+                FC_LOG("Assembly : Distance joint '" << joint->getFullName()
+                       << "' — DistanceType=" << distanceTypeName(distType)
+                       << ", kind=" << static_cast<int>(kind)
+                       << ", distance=" << distance);
                 break;
             }
             default:
@@ -1323,6 +1406,23 @@ KCSolve::SolveContext AssemblyObject::buildSolveContext(
         ctx.simulation = sp;
     }
 
+    // Log context summary
+    {
+        int nGrounded = 0, nFree = 0, nLimits = 0;
+        for (const auto& p : ctx.parts) {
+            if (p.grounded) nGrounded++;
+            else nFree++;
+        }
+        for (const auto& c : ctx.constraints) {
+            if (!c.limits.empty()) nLimits++;
+        }
+        FC_LOG("Assembly : buildSolveContext — "
+               << nGrounded << " grounded + " << nFree << " free parts, "
+               << ctx.constraints.size() << " constraints"
+               << (nLimits ? (std::string(", ") + std::to_string(nLimits) + " with limits") : "")
+               << (ctx.bundle_fixed ? ", bundle_fixed=true" : ""));
+    }
+
     return ctx;
 }
 

src/Mod/Assembly/App/AssemblyObject.h

@@ -84,6 +84,7 @@ public:
         return "AssemblyGui::ViewProviderAssembly";
     }
 
+    void setupObject() override;
     App::DocumentObjectExecReturn* execute() override;
     void onChanged(const App::Property* prop) override;
     /* Solve the assembly. It will update first the joints, solve, update placements of the parts
@@ -279,6 +280,10 @@ private:
 
     bool bundleFixed;
 
+    // Drag diagnostic counters (reset in preDrag, reported in postDrag)
+    int dragStepCount_ = 0;
+    int dragStepRejected_ = 0;
+
     int lastDoF;
     bool lastHasConflict;
     bool lastHasRedundancies;

src/Mod/Assembly/App/AssemblyUtils.cpp

@@ -23,6 +23,7 @@
 
 #include <BRepAdaptor_Curve.hxx>
 #include <BRepAdaptor_Surface.hxx>
+#include <TopExp_Explorer.hxx>
 #include <TopoDS.hxx>
 #include <TopoDS_Face.hxx>
 #include <gp_Circ.hxx>
@@ -54,10 +55,56 @@
 
 namespace PartApp = Part;
 
+FC_LOG_LEVEL_INIT("Assembly", true, true, true)
+
 // ======================================= Utils ======================================
 namespace Assembly
 {
 
+const char* distanceTypeName(DistanceType dt)
+{
+    switch (dt) {
+        case DistanceType::PointPoint:       return "PointPoint";
+        case DistanceType::LineLine:         return "LineLine";
+        case DistanceType::LineCircle:       return "LineCircle";
+        case DistanceType::CircleCircle:     return "CircleCircle";
+        case DistanceType::PlanePlane:       return "PlanePlane";
+        case DistanceType::PlaneCylinder:    return "PlaneCylinder";
+        case DistanceType::PlaneSphere:      return "PlaneSphere";
+        case DistanceType::PlaneCone:        return "PlaneCone";
+        case DistanceType::PlaneTorus:       return "PlaneTorus";
+        case DistanceType::CylinderCylinder: return "CylinderCylinder";
+        case DistanceType::CylinderSphere:   return "CylinderSphere";
+        case DistanceType::CylinderCone:     return "CylinderCone";
+        case DistanceType::CylinderTorus:    return "CylinderTorus";
+        case DistanceType::ConeCone:         return "ConeCone";
+        case DistanceType::ConeTorus:        return "ConeTorus";
+        case DistanceType::ConeSphere:       return "ConeSphere";
+        case DistanceType::TorusTorus:       return "TorusTorus";
+        case DistanceType::TorusSphere:      return "TorusSphere";
+        case DistanceType::SphereSphere:     return "SphereSphere";
+        case DistanceType::PointPlane:       return "PointPlane";
+        case DistanceType::PointCylinder:    return "PointCylinder";
+        case DistanceType::PointSphere:      return "PointSphere";
+        case DistanceType::PointCone:        return "PointCone";
+        case DistanceType::PointTorus:       return "PointTorus";
+        case DistanceType::LinePlane:        return "LinePlane";
+        case DistanceType::LineCylinder:     return "LineCylinder";
+        case DistanceType::LineSphere:       return "LineSphere";
+        case DistanceType::LineCone:         return "LineCone";
+        case DistanceType::LineTorus:        return "LineTorus";
+        case DistanceType::CurvePlane:       return "CurvePlane";
+        case DistanceType::CurveCylinder:    return "CurveCylinder";
+        case DistanceType::CurveSphere:      return "CurveSphere";
+        case DistanceType::CurveCone:        return "CurveCone";
+        case DistanceType::CurveTorus:       return "CurveTorus";
+        case DistanceType::PointLine:        return "PointLine";
+        case DistanceType::PointCurve:       return "PointCurve";
+        case DistanceType::Other:            return "Other";
+    }
+    return "Unknown";
+}
+
 void swapJCS(const App::DocumentObject* joint)
 {
     if (!joint) {
@@ -151,6 +198,120 @@ double getEdgeRadius(const App::DocumentObject* obj, const std::string& elt)
     return sf.GetType() == GeomAbs_Circle ? sf.Circle().Radius() : 0.0;
 }
 
+/// Determine whether \a obj represents a planar datum when referenced with an
+/// empty element type (bare sub-name ending with ".").
+///
+/// Covers three independent class hierarchies:
+///   1. App::Plane  (origin planes, Part::DatumPlane)
+///   2. Part::Datum (PartDesign::Plane — not derived from App::Plane)
+///   3. Any Part::Feature whose whole-object shape is a single planar face
+///      (e.g. Part::Plane primitive referenced without an element)
+static bool isDatumPlane(const App::DocumentObject* obj)
+{
+    if (!obj) {
+        return false;
+    }
+
+    // Origin planes and Part::DatumPlane (both inherit App::Plane).
+    if (obj->isDerivedFrom<App::Plane>()) {
+        return true;
+    }
+
+    // PartDesign datum objects inherit Part::Datum but NOT App::Plane.
+    // Part::Datum is also the base for PartDesign::Line and PartDesign::Point,
+    // so inspect the shape to confirm it is actually planar.
+    if (obj->isDerivedFrom<PartApp::Datum>()) {
+        auto* feat = static_cast<const PartApp::Feature*>(obj);
+        const auto& shape = feat->Shape.getShape().getShape();
+        if (shape.IsNull()) {
+            return false;
+        }
+        TopExp_Explorer ex(shape, TopAbs_FACE);
+        if (ex.More()) {
+            BRepAdaptor_Surface sf(TopoDS::Face(ex.Current()));
+            return sf.GetType() == GeomAbs_Plane;
+        }
+        return false;
+    }
+
+    // Fallback for any Part::Feature (e.g. Part::Plane primitive) referenced
+    // bare — if its shape is a single planar face, treat it as a datum plane.
+    if (auto* feat = dynamic_cast<const PartApp::Feature*>(obj)) {
+        const auto& shape = feat->Shape.getShape().getShape();
+        if (shape.IsNull()) {
+            return false;
+        }
+        TopExp_Explorer ex(shape, TopAbs_FACE);
+        if (!ex.More()) {
+            return false;
+        }
+        BRepAdaptor_Surface sf(TopoDS::Face(ex.Current()));
+        if (sf.GetType() != GeomAbs_Plane) {
+            return false;
+        }
+        ex.Next();
+        // Only treat as datum if there is exactly one face — a multi-face
+        // solid referenced bare is ambiguous and should not be classified.
+        return !ex.More();
+    }
+
+    return false;
+}
+
+/// Same idea for datum lines (App::Line, PartDesign::Line, etc.).
+static bool isDatumLine(const App::DocumentObject* obj)
+{
+    if (!obj) {
+        return false;
+    }
+
+    if (obj->isDerivedFrom<App::Line>()) {
+        return true;
+    }
+
+    if (obj->isDerivedFrom<PartApp::Datum>()) {
+        auto* feat = static_cast<const PartApp::Feature*>(obj);
+        const auto& shape = feat->Shape.getShape().getShape();
+        if (shape.IsNull()) {
+            return false;
+        }
+        TopExp_Explorer ex(shape, TopAbs_EDGE);
+        if (ex.More()) {
+            BRepAdaptor_Curve cv(TopoDS::Edge(ex.Current()));
+            return cv.GetType() == GeomAbs_Line;
+        }
+        return false;
+    }
+
+    return false;
+}
+
+/// Same idea for datum points (App::Point, PartDesign::Point, etc.).
+static bool isDatumPoint(const App::DocumentObject* obj)
+{
+    if (!obj) {
+        return false;
+    }
+
+    if (obj->isDerivedFrom<App::Point>()) {
+        return true;
+    }
+
+    if (obj->isDerivedFrom<PartApp::Datum>()) {
+        auto* feat = static_cast<const PartApp::Feature*>(obj);
+        const auto& shape = feat->Shape.getShape().getShape();
+        if (shape.IsNull()) {
+            return false;
+        }
+        // A datum point has a vertex but no edges or faces.
+        TopExp_Explorer exE(shape, TopAbs_EDGE);
+        TopExp_Explorer exV(shape, TopAbs_VERTEX);
+        return !exE.More() && exV.More();
+    }
+
+    return false;
+}
+
 DistanceType getDistanceType(App::DocumentObject* joint)
 {
     if (!joint) {
@@ -164,6 +325,179 @@ DistanceType getDistanceType(App::DocumentObject* joint)
     auto* obj1 = getLinkedObjFromRef(joint, "Reference1");
     auto* obj2 = getLinkedObjFromRef(joint, "Reference2");
 
+    // Datum objects referenced bare have empty element types (sub-name
+    // ends with ".").  PartDesign datums referenced through a body can
+    // also produce non-standard element types like "Plane" (from a
+    // sub-name such as "Body.DatumPlane.Plane" — Part::Datum::getSubObject
+    // ignores the trailing element, but splitSubName still extracts it).
+    //
+    // Detect these before the main geometry chain, which only handles
+    // the standard Face/Edge/Vertex element types.
+    //
+    // isDatumPlane/Line/Point cover all three independent hierarchies:
+    //   - App::Plane / App::Line / App::Point  (origin datums)
+    //   - Part::Datum subclasses               (PartDesign datums)
+    //   - Part::Feature with single-face shape  (Part::Plane primitive, bare ref)
+    auto isNonGeomElement = [](const std::string& t) {
+        return t != "Face" && t != "Edge" && t != "Vertex";
+    };
+    const bool datumPlane1 = isNonGeomElement(type1) && isDatumPlane(obj1);
+    const bool datumPlane2 = isNonGeomElement(type2) && isDatumPlane(obj2);
+    const bool datumLine1  = isNonGeomElement(type1) && !datumPlane1 && isDatumLine(obj1);
+    const bool datumLine2  = isNonGeomElement(type2) && !datumPlane2 && isDatumLine(obj2);
+    const bool datumPoint1 = isNonGeomElement(type1) && !datumPlane1 && !datumLine1 && isDatumPoint(obj1);
+    const bool datumPoint2 = isNonGeomElement(type2) && !datumPlane2 && !datumLine2 && isDatumPoint(obj2);
+    const bool datum1 = datumPlane1 || datumLine1 || datumPoint1;
+    const bool datum2 = datumPlane2 || datumLine2 || datumPoint2;
+
+    if (datum1 || datum2) {
+        // Map each datum side to a synthetic element type so the same
+        // classification logic applies regardless of which hierarchy
+        // the object comes from.
+        auto syntheticType = [](bool isPlane, bool isLine, bool isPoint,
+                                const std::string& elemType) -> std::string {
+            if (isPlane)  return "Face";
+            if (isLine)   return "Edge";
+            if (isPoint)  return "Vertex";
+            return elemType;  // non-datum side keeps its real type
+        };
+
+        const std::string syn1 = syntheticType(datumPlane1, datumLine1, datumPoint1, type1);
+        const std::string syn2 = syntheticType(datumPlane2, datumLine2, datumPoint2, type2);
+
+        // Both sides are datum planes.
+        if (datumPlane1 && datumPlane2) {
+            FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                   << "') — datum+datum → PlanePlane");
+            return DistanceType::PlanePlane;
+        }
+
+        // One side is a datum plane, the other has a real element type
+        // (or is another datum kind).
+        // For PointPlane/LinePlane, the solver's PointInPlaneConstraint
+        // reads the plane normal from marker_j (Reference2).  Unlike
+        // real Face+Vertex joints (where both Placements carry the
+        // face normal from findPlacement), datum planes only carry
+        // their normal through computeMarkerTransform.  So the datum
+        // plane must end up on Reference2 for the normal to reach marker_j.
+        //
+        // For PlanePlane the convention matches the existing Face+Face
+        // path (plane on Reference1).
+        if (datumPlane1 || datumPlane2) {
+            const auto& otherSyn = datumPlane1 ? syn2 : syn1;
+
+            if (otherSyn == "Vertex" || otherSyn == "Edge") {
+                // Datum plane must be on Reference2 (j side).
+                if (datumPlane1) {
+                    swapJCS(joint);  // move datum from Ref1 → Ref2
+                }
+                DistanceType result = (otherSyn == "Vertex")
+                    ? DistanceType::PointPlane : DistanceType::LinePlane;
+                FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                       << "') — datum+" << otherSyn << " → "
+                       << distanceTypeName(result)
+                       << (datumPlane1 ? " (swapped)" : ""));
+                return result;
+            }
+
+            // Face + datum plane or datum plane + datum plane → PlanePlane.
+            // No swap needed: PlanarConstraint is symmetric (uses both
+            // z_i and z_j), and preserving the original Reference order
+            // keeps the initial Placement values consistent so the solver
+            // stays in the correct orientation branch.
+            FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                   << "') — datum+" << otherSyn << " → PlanePlane");
+            return DistanceType::PlanePlane;
+        }
+
+        // Datum line or datum point paired with a real element type.
+        // Map to the appropriate pair using synthetic types and fall
+        // through to the main geometry chain below.  The synthetic
+        // types ("Edge", "Vertex") will match the existing if-else
+        // branches — but those branches call isEdgeType/isFaceType on
+        // the object, which requires a real sub-element name.  For
+        // datum lines/points the element is empty, so we classify
+        // directly here.
+        if (datumLine1 && datumLine2) {
+            FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                   << "') — datumLine+datumLine → LineLine");
+            return DistanceType::LineLine;
+        }
+        if (datumPoint1 && datumPoint2) {
+            FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                   << "') — datumPoint+datumPoint → PointPoint");
+            return DistanceType::PointPoint;
+        }
+        if ((datumLine1 && datumPoint2) || (datumPoint1 && datumLine2)) {
+            if (datumPoint1) {
+                swapJCS(joint);  // line first
+            }
+            FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                   << "') — datumLine+datumPoint → PointLine");
+            return DistanceType::PointLine;
+        }
+
+        // One datum line/point + one real element type.
+        if (datumLine1 || datumLine2) {
+            const auto& otherSyn = datumLine1 ? syn2 : syn1;
+            if (otherSyn == "Face") {
+                // Line + Face — need line on Reference2 (edge side).
+                if (datumLine1) {
+                    swapJCS(joint);
+                }
+                // We don't know the face type without inspecting the shape,
+                // but LinePlane is the most common and safest classification.
+                FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                       << "') — datumLine+Face → LinePlane");
+                return DistanceType::LinePlane;
+            }
+            if (otherSyn == "Vertex") {
+                if (datumLine2) {
+                    swapJCS(joint);  // line first
+                }
+                FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                       << "') — datumLine+Vertex → PointLine");
+                return DistanceType::PointLine;
+            }
+            if (otherSyn == "Edge") {
+                FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                       << "') — datumLine+Edge → LineLine");
+                return DistanceType::LineLine;
+            }
+        }
+        if (datumPoint1 || datumPoint2) {
+            const auto& otherSyn = datumPoint1 ? syn2 : syn1;
+            if (otherSyn == "Face") {
+                // Point + Face — face first, point second.
+                if (!datumPoint2) {
+                    swapJCS(joint);  // put face on Ref1
+                }
+                FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                       << "') — datumPoint+Face → PointPlane");
+                return DistanceType::PointPlane;
+            }
+            if (otherSyn == "Edge") {
+                // Edge first, point second.
+                if (datumPoint1) {
+                    swapJCS(joint);
+                }
+                FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                       << "') — datumPoint+Edge → PointLine");
+                return DistanceType::PointLine;
+            }
+            if (otherSyn == "Vertex") {
+                FC_LOG("Assembly : getDistanceType('" << joint->getFullName()
+                       << "') — datumPoint+Vertex → PointPoint");
+                return DistanceType::PointPoint;
+            }
+        }
+
+        // If we get here, it's an unrecognized datum combination.
+        FC_WARN("Assembly : getDistanceType('" << joint->getFullName()
+                << "') — unrecognized datum combination (syn1="
+                << syn1 << ", syn2=" << syn2 << ")");
+    }
+
     if (type1 == "Vertex" && type2 == "Vertex") {
         return DistanceType::PointPoint;
     }
@@ -591,6 +925,19 @@ App::DocumentObject* getObjFromRef(App::DocumentObject* comp, const std::string&
         if (obj->isDerivedFrom<App::Part>() || obj->isLinkGroup()) {
             continue;
         }
+        else if (obj->isDerivedFrom<App::LocalCoordinateSystem>()) {
+            // Resolve LCS → child datum element (e.g. Origin → XY_Plane)
+            auto nextIt = std::next(it);
+            if (nextIt != names.end()) {
+                for (auto* child : obj->getOutList()) {
+                    if (child->getNameInDocument() == *nextIt
+                        && child->isDerivedFrom<App::DatumElement>()) {
+                        return child;
+                    }
+                }
+            }
+            return obj;
+        }
         else if (obj->isDerivedFrom<PartDesign::Body>()) {
             return handlePartDesignBody(obj, it);
         }

src/Mod/Assembly/App/AssemblyUtils.h

@@ -148,6 +148,7 @@ AssemblyExport double getFaceRadius(const App::DocumentObject* obj, const std::s
 AssemblyExport double getEdgeRadius(const App::DocumentObject* obj, const std::string& elName);
 
 AssemblyExport DistanceType getDistanceType(App::DocumentObject* joint);
+AssemblyExport const char* distanceTypeName(DistanceType dt);
 AssemblyExport JointGroup* getJointGroup(const App::Part* part);
 
 AssemblyExport std::vector<App::DocumentObject*> getAssemblyComponents(const AssemblyObject* assembly);

src/Mod/Assembly/AssemblyTests/TestAssemblyOriginPlanes.py

@@ -0,0 +1,314 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+# /****************************************************************************
+#                                                                           *
+#    Copyright (c) 2025 Kindred Systems <development@kindred-systems.com>   *
+#                                                                           *
+#    This file is part of FreeCAD.                                          *
+#                                                                           *
+#    FreeCAD is free software: you can redistribute it and/or modify it     *
+#    under the terms of the GNU Lesser General Public License as            *
+#    published by the Free Software Foundation, either version 2.1 of the   *
+#    License, or (at your option) any later version.                        *
+#                                                                           *
+#    FreeCAD is distributed in the hope that it will be useful, but         *
+#    WITHOUT ANY WARRANTY; without even the implied warranty of             *
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU       *
+#    Lesser General Public License for more details.                        *
+#                                                                           *
+#    You should have received a copy of the GNU Lesser General Public       *
+#    License along with FreeCAD. If not, see                                *
+#    <https://www.gnu.org/licenses/>.                                       *
+#                                                                           *
+# ***************************************************************************/
+
+"""
+Tests for assembly origin reference planes.
+
+Verifies that new assemblies have properly labeled, grounded origin planes
+and that joints can reference them for solving.
+"""
+
+import os
+import tempfile
+import unittest
+
+import FreeCAD as App
+import JointObject
+import UtilsAssembly
+
+
+class TestAssemblyOriginPlanes(unittest.TestCase):
+    """Tests for assembly origin planes (Top/Front/Right)."""
+
+    def setUp(self):
+        doc_name = self.__class__.__name__
+        if App.ActiveDocument:
+            if App.ActiveDocument.Name != doc_name:
+                App.newDocument(doc_name)
+        else:
+            App.newDocument(doc_name)
+        App.setActiveDocument(doc_name)
+        self.doc = App.ActiveDocument
+
+        self.assembly = self.doc.addObject("Assembly::AssemblyObject", "Assembly")
+        self.jointgroup = self.assembly.newObject("Assembly::JointGroup", "Joints")
+
+    def tearDown(self):
+        App.closeDocument(self.doc.Name)
+
+    # ── Helpers ─────────────────────────────────────────────────────
+
+    def _get_origin(self):
+        return self.assembly.Origin
+
+    def _make_box(self, x=0, y=0, z=0, size=10):
+        box = self.assembly.newObject("Part::Box", "Box")
+        box.Length = size
+        box.Width = size
+        box.Height = size
+        box.Placement = App.Placement(App.Vector(x, y, z), App.Rotation())
+        return box
+
+    def _make_joint(self, joint_type, ref1, ref2):
+        joint = self.jointgroup.newObject("App::FeaturePython", "Joint")
+        JointObject.Joint(joint, joint_type)
+        refs = [
+            [ref1[0], ref1[1]],
+            [ref2[0], ref2[1]],
+        ]
+        joint.Proxy.setJointConnectors(joint, refs)
+        return joint
+
+    # ── Structure tests ─────────────────────────────────────────────
+
+    def test_assembly_has_origin(self):
+        """New assembly has an Origin with 3 planes, 3 axes, 1 point."""
+        origin = self._get_origin()
+        self.assertIsNotNone(origin)
+        self.assertTrue(origin.isDerivedFrom("App::LocalCoordinateSystem"))
+
+        planes = origin.planes()
+        self.assertEqual(len(planes), 3)
+
+        axes = origin.axes()
+        self.assertEqual(len(axes), 3)
+
+    def test_origin_planes_labeled(self):
+        """Origin planes are labeled Top, Front, Right."""
+        origin = self._get_origin()
+
+        xy = origin.getXY()
+        xz = origin.getXZ()
+        yz = origin.getYZ()
+
+        self.assertEqual(xy.Label, "Top")
+        self.assertEqual(xz.Label, "Front")
+        self.assertEqual(yz.Label, "Right")
+
+    def test_origin_planes_have_correct_roles(self):
+        """Origin planes retain correct internal Role names."""
+        origin = self._get_origin()
+
+        self.assertEqual(origin.getXY().Role, "XY_Plane")
+        self.assertEqual(origin.getXZ().Role, "XZ_Plane")
+        self.assertEqual(origin.getYZ().Role, "YZ_Plane")
+
+    # ── Grounding tests ─────────────────────────────────────────────
+
+    def test_origin_in_grounded_set(self):
+        """Origin is part of the assembly's grounded set."""
+        grounded = self.assembly.getGroundedParts()
+        origin = self._get_origin()
+
+        grounded_names = {obj.Name for obj in grounded}
+        self.assertIn(origin.Name, grounded_names)
+
+    # ── Reference resolution tests ──────────────────────────────────
+
+    def test_getObject_resolves_origin_plane(self):
+        """UtilsAssembly.getObject correctly resolves an origin plane ref."""
+        origin = self._get_origin()
+        xy = origin.getXY()
+
+        # Ref structure: [Origin, ["XY_Plane.", "XY_Plane."]]
+        ref = [origin, [xy.Name + ".", xy.Name + "."]]
+        obj = UtilsAssembly.getObject(ref)
+        self.assertEqual(obj, xy)
+
+    def test_findPlacement_origin_plane_returns_identity(self):
+        """findPlacement for an origin plane (whole-object) returns identity."""
+        origin = self._get_origin()
+        xy = origin.getXY()
+
+        ref = [origin, [xy.Name + ".", xy.Name + "."]]
+        plc = UtilsAssembly.findPlacement(ref)
+
+        # For datum planes with no element, identity is returned.
+        # The actual orientation comes from the solver's getGlobalPlacement.
+        self.assertTrue(
+            plc.isSame(App.Placement(), 1e-6),
+            "findPlacement for origin plane should return identity",
+        )
+
+    # ── Joint / solve tests ─────────────────────────────────────────
+
+    def test_fixed_joint_to_origin_plane(self):
+        """Fixed joint referencing an origin plane solves correctly."""
+        origin = self._get_origin()
+        xy = origin.getXY()
+
+        box = self._make_box(50, 50, 50)
+
+        # Fixed joint (type 0): origin XY plane ↔ box Face1 (bottom, Z=0)
+        self._make_joint(
+            0,
+            [origin, [xy.Name + ".", xy.Name + "."]],
+            [box, ["Face1", "Vertex1"]],
+        )
+
+        # After solve, the box should have moved so that its Face1 (bottom)
+        # aligns with the XY plane (Z=0). The box bottom vertex1 is at (0,0,0).
+        self.assertAlmostEqual(
+            box.Placement.Base.z,
+            0.0,
+            places=3,
+            msg="Box should be on XY plane after fixed joint to Top plane",
+        )
+
+    def test_solve_return_code_with_origin_plane(self):
+        """Solve with an origin plane joint returns success (0)."""
+        origin = self._get_origin()
+        xz = origin.getXZ()
+
+        box = self._make_box(0, 100, 0)
+
+        self._make_joint(
+            0,
+            [origin, [xz.Name + ".", xz.Name + "."]],
+            [box, ["Face1", "Vertex1"]],
+        )
+
+        result = self.assembly.solve()
+        self.assertEqual(result, 0, "Solve should succeed with origin plane joint")
+
+    # ── Distance joint to datum plane tests ────────────────────────
+
+    def test_distance_vertex_to_datum_plane_solves(self):
+        """Distance(0) joint: vertex → datum plane solves and pins position."""
+        origin = self._get_origin()
+        xy = origin.getXY()  # Top (Z normal)
+        xz = origin.getXZ()  # Front (Y normal)
+        yz = origin.getYZ()  # Right (X normal)
+
+        box = self._make_box(50, 50, 50)
+
+        # 3 Distance joints, each vertex→datum, distance=0.
+        # This should pin the box's Vertex1 (corner at local 0,0,0) to the
+        # origin, giving 3 PointInPlane constraints (1 residual each = 3 total).
+        for plane in [xy, xz, yz]:
+            joint = self._make_joint(
+                5,  # Distance
+                [box, ["Vertex1", "Vertex1"]],
+                [origin, [plane.Name + ".", plane.Name + "."]],
+            )
+            joint.Distance = 0.0
+
+        result = self.assembly.solve()
+        self.assertEqual(
+            result, 0, "Solve should succeed for vertex→datum Distance joints"
+        )
+
+        # The box's Vertex1 (at local 0,0,0) should be at the origin.
+        v = box.Placement.Base
+        self.assertAlmostEqual(v.x, 0.0, places=2, msg="X should be pinned to 0")
+        self.assertAlmostEqual(v.y, 0.0, places=2, msg="Y should be pinned to 0")
+        self.assertAlmostEqual(v.z, 0.0, places=2, msg="Z should be pinned to 0")
+
+    def test_distance_vertex_to_datum_plane_preserves_orientation(self):
+        """Distance(0) vertex→datum should not constrain orientation."""
+        origin = self._get_origin()
+        xy = origin.getXY()
+        xz = origin.getXZ()
+        yz = origin.getYZ()
+
+        # Start box with a known rotation (45° about Z).
+        rot = App.Rotation(App.Vector(0, 0, 1), 45)
+        box = self._make_box(50, 50, 50)
+        box.Placement = App.Placement(App.Vector(50, 50, 50), rot)
+
+        for plane in [xy, xz, yz]:
+            joint = self._make_joint(
+                5,
+                [box, ["Vertex1", "Vertex1"]],
+                [origin, [plane.Name + ".", plane.Name + "."]],
+            )
+            joint.Distance = 0.0
+
+        self.assembly.solve()
+
+        # 3 PointInPlane constraints pin position (3 DOF) but leave
+        # orientation free (3 DOF).  The solver should keep the original
+        # orientation since it's the lowest-energy solution from the
+        # initial placement.
+        dof = self.assembly.getLastDoF()
+        self.assertEqual(
+            dof, 3, "3 PointInPlane constraints should leave 3 DOF (orientation)"
+        )
+
+    def test_distance_face_to_datum_plane_solves(self):
+        """Distance(0) joint: face → datum plane solves (PlanePlane/Planar)."""
+        origin = self._get_origin()
+        xy = origin.getXY()
+
+        box = self._make_box(0, 0, 50)
+
+        # Face1 is the -Z face of a Part::Box.
+        joint = self._make_joint(
+            5,
+            [box, ["Face1", "Vertex1"]],
+            [origin, [xy.Name + ".", xy.Name + "."]],
+        )
+        joint.Distance = 0.0
+
+        result = self.assembly.solve()
+        self.assertEqual(
+            result, 0, "Solve should succeed for face→datum Distance joint"
+        )
+
+    # ── Round-trip test ──────────────────────────────────────────────
+
+    def test_save_load_preserves_labels(self):
+        """Labels survive save/load round-trip."""
+        origin = self._get_origin()
+
+        # Verify labels before save
+        self.assertEqual(origin.getXY().Label, "Top")
+        self.assertEqual(origin.getXZ().Label, "Front")
+        self.assertEqual(origin.getYZ().Label, "Right")
+
+        # Save to temp file
+        tmp = tempfile.mktemp(suffix=".FCStd")
+        try:
+            self.doc.saveAs(tmp)
+
+            # Close and reopen
+            doc_name = self.doc.Name
+            App.closeDocument(doc_name)
+            App.openDocument(tmp)
+            doc = App.ActiveDocument
+
+            assembly = doc.getObject("Assembly")
+            self.assertIsNotNone(assembly)
+
+            origin = assembly.Origin
+            self.assertEqual(origin.getXY().Label, "Top")
+            self.assertEqual(origin.getXZ().Label, "Front")
+            self.assertEqual(origin.getYZ().Label, "Right")
+
+            App.closeDocument(doc.Name)
+        finally:
+            if os.path.exists(tmp):
+                os.remove(tmp)
+
+        # Reopen a fresh doc for tearDown
+        App.newDocument(self.__class__.__name__)

src/Mod/Assembly/AssemblyTests/TestDatumClassification.py

@@ -0,0 +1,266 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+# /****************************************************************************
+#                                                                           *
+#    Copyright (c) 2025 Kindred Systems <development@kindred-systems.com>   *
+#                                                                           *
+#    This file is part of FreeCAD.                                          *
+#                                                                           *
+#    FreeCAD is free software: you can redistribute it and/or modify it     *
+#    under the terms of the GNU Lesser General Public License as            *
+#    published by the Free Software Foundation, either version 2.1 of the   *
+#    License, or (at your option) any later version.                        *
+#                                                                           *
+#    FreeCAD is distributed in the hope that it will be useful, but         *
+#    WITHOUT ANY WARRANTY; without even the implied warranty of             *
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU       *
+#    Lesser General Public License for more details.                        *
+#                                                                           *
+#    You should have received a copy of the GNU Lesser General Public       *
+#    License along with FreeCAD. If not, see                                *
+#    <https://www.gnu.org/licenses/>.                                       *
+#                                                                           *
+# ***************************************************************************/
+
+"""
+Tests for datum plane classification in Distance joints.
+
+Verifies that getDistanceType correctly classifies joints involving datum
+planes from all three class hierarchies:
+  1. App::Plane          — origin planes (XY, XZ, YZ)
+  2. PartDesign::Plane   — datum planes inside a PartDesign body
+  3. Part::Plane         — Part workbench plane primitives (bare reference)
+"""
+
+import unittest
+
+import FreeCAD as App
+import JointObject
+
+
+class TestDatumClassification(unittest.TestCase):
+    """Tests that Distance joints with datum plane references are
+    classified as PlanePlane (not Other) regardless of the datum
+    object's class hierarchy."""
+
+    def setUp(self):
+        doc_name = self.__class__.__name__
+        if App.ActiveDocument:
+            if App.ActiveDocument.Name != doc_name:
+                App.newDocument(doc_name)
+        else:
+            App.newDocument(doc_name)
+        App.setActiveDocument(doc_name)
+        self.doc = App.ActiveDocument
+
+        self.assembly = self.doc.addObject("Assembly::AssemblyObject", "Assembly")
+        self.jointgroup = self.assembly.newObject("Assembly::JointGroup", "Joints")
+
+    def tearDown(self):
+        App.closeDocument(self.doc.Name)
+
+    # ── Helpers ─────────────────────────────────────────────────────
+
+    def _make_box(self, x=0, y=0, z=0, size=10):
+        box = self.assembly.newObject("Part::Box", "Box")
+        box.Length = size
+        box.Width = size
+        box.Height = size
+        box.Placement = App.Placement(App.Vector(x, y, z), App.Rotation())
+        return box
+
+    def _make_joint(self, joint_type, ref1, ref2):
+        joint = self.jointgroup.newObject("App::FeaturePython", "Joint")
+        JointObject.Joint(joint, joint_type)
+        refs = [
+            [ref1[0], ref1[1]],
+            [ref2[0], ref2[1]],
+        ]
+        joint.Proxy.setJointConnectors(joint, refs)
+        return joint
+
+    def _make_pd_body_with_datum_plane(self, name="Body"):
+        """Create a PartDesign::Body with a datum plane inside the assembly."""
+        body = self.assembly.newObject("PartDesign::Body", name)
+        datum = body.newObject("PartDesign::Plane", "DatumPlane")
+        self.doc.recompute()
+        return body, datum
+
+    def _make_part_plane(self, name="PartPlane"):
+        """Create a Part::Plane primitive inside the assembly."""
+        plane = self.assembly.newObject("Part::Plane", name)
+        plane.Length = 10
+        plane.Width = 10
+        self.doc.recompute()
+        return plane
+
+    # ── Origin plane tests (App::Plane — existing behaviour) ───────
+
+    def test_origin_plane_face_classified_as_plane_plane(self):
+        """Distance joint: box Face → origin datum plane → PlanePlane."""
+        origin = self.assembly.Origin
+        xy = origin.getXY()
+        box = self._make_box(0, 0, 50)
+
+        joint = self._make_joint(
+            5,  # Distance
+            [box, ["Face1", "Vertex1"]],
+            [origin, [xy.Name + ".", xy.Name + "."]],
+        )
+        joint.Distance = 0.0
+
+        result = self.assembly.solve()
+        self.assertEqual(
+            result,
+            0,
+            "Distance joint with origin plane should solve (not produce Other)",
+        )
+
+    # ── PartDesign::Plane tests ────────────────────────────────────
+
+    def test_pd_datum_plane_face_classified_as_plane_plane(self):
+        """Distance joint: box Face → PartDesign::Plane → PlanePlane."""
+        body, datum = self._make_pd_body_with_datum_plane()
+        box = self._make_box(0, 0, 50)
+
+        # Ground the body so the solver has a fixed reference.
+        gnd = self.jointgroup.newObject("App::FeaturePython", "GroundedJoint")
+        JointObject.GroundedJoint(gnd, body)
+
+        # Reference the datum plane with a bare sub-name (ends with ".").
+        joint = self._make_joint(
+            5,  # Distance
+            [box, ["Face1", "Vertex1"]],
+            [body, [datum.Name + ".", datum.Name + "."]],
+        )
+        joint.Distance = 0.0
+
+        result = self.assembly.solve()
+        self.assertNotEqual(
+            result,
+            -1,
+            "Distance joint with PartDesign::Plane should not fail to solve "
+            "(DistanceType should be PlanePlane, not Other)",
+        )
+
+    def test_pd_datum_plane_vertex_classified_as_point_plane(self):
+        """Distance joint: box Vertex → PartDesign::Plane → PointPlane."""
+        body, datum = self._make_pd_body_with_datum_plane()
+        box = self._make_box(0, 0, 50)
+
+        gnd = self.jointgroup.newObject("App::FeaturePython", "GroundedJoint")
+        JointObject.GroundedJoint(gnd, body)
+
+        joint = self._make_joint(
+            5,  # Distance
+            [box, ["Vertex1", "Vertex1"]],
+            [body, [datum.Name + ".", datum.Name + "."]],
+        )
+        joint.Distance = 0.0
+
+        result = self.assembly.solve()
+        self.assertNotEqual(
+            result,
+            -1,
+            "Distance joint vertex → PartDesign::Plane should not fail "
+            "(DistanceType should be PointPlane, not Other)",
+        )
+
+    def test_two_pd_datum_planes_classified_as_plane_plane(self):
+        """Distance joint: PartDesign::Plane → PartDesign::Plane → PlanePlane."""
+        body1, datum1 = self._make_pd_body_with_datum_plane("Body1")
+        body2, datum2 = self._make_pd_body_with_datum_plane("Body2")
+
+        gnd = self.jointgroup.newObject("App::FeaturePython", "GroundedJoint")
+        JointObject.GroundedJoint(gnd, body1)
+
+        joint = self._make_joint(
+            5,  # Distance
+            [body1, [datum1.Name + ".", datum1.Name + "."]],
+            [body2, [datum2.Name + ".", datum2.Name + "."]],
+        )
+        joint.Distance = 0.0
+
+        result = self.assembly.solve()
+        self.assertNotEqual(
+            result,
+            -1,
+            "Distance joint PartDesign::Plane → PartDesign::Plane should not fail "
+            "(DistanceType should be PlanePlane, not Other)",
+        )
+
+    # ── Part::Plane tests (primitive, bare reference) ──────────────
+
+    def test_part_plane_bare_ref_face_classified_as_plane_plane(self):
+        """Distance joint: box Face → Part::Plane (bare ref) → PlanePlane."""
+        plane = self._make_part_plane()
+        box = self._make_box(0, 0, 50)
+
+        gnd = self.jointgroup.newObject("App::FeaturePython", "GroundedJoint")
+        JointObject.GroundedJoint(gnd, plane)
+
+        # Bare reference to Part::Plane (sub-name ends with ".").
+        joint = self._make_joint(
+            5,  # Distance
+            [box, ["Face1", "Vertex1"]],
+            [plane, [".", "."]],
+        )
+        joint.Distance = 0.0
+
+        result = self.assembly.solve()
+        self.assertNotEqual(
+            result,
+            -1,
+            "Distance joint with Part::Plane (bare ref) should not fail "
+            "(DistanceType should be PlanePlane, not Other)",
+        )
+
+    def test_part_plane_with_face1_classified_as_plane_plane(self):
+        """Distance joint: box Face → Part::Plane Face1 → PlanePlane.
+
+        When Part::Plane is referenced with an explicit Face1 element,
+        it should enter the normal Face+Face classification path."""
+        plane = self._make_part_plane()
+        box = self._make_box(0, 0, 50)
+
+        gnd = self.jointgroup.newObject("App::FeaturePython", "GroundedJoint")
+        JointObject.GroundedJoint(gnd, plane)
+
+        joint = self._make_joint(
+            5,  # Distance
+            [box, ["Face1", "Vertex1"]],
+            [plane, ["Face1", "Vertex1"]],
+        )
+        joint.Distance = 0.0
+
+        result = self.assembly.solve()
+        self.assertNotEqual(
+            result,
+            -1,
+            "Distance joint with Part::Plane Face1 should solve normally",
+        )
+
+    # ── Cross-hierarchy tests ──────────────────────────────────────
+
+    def test_origin_plane_and_pd_datum_classified_as_plane_plane(self):
+        """Distance joint: origin App::Plane → PartDesign::Plane → PlanePlane."""
+        origin = self.assembly.Origin
+        xy = origin.getXY()
+        body, datum = self._make_pd_body_with_datum_plane()
+
+        gnd = self.jointgroup.newObject("App::FeaturePython", "GroundedJoint")
+        JointObject.GroundedJoint(gnd, body)
+
+        joint = self._make_joint(
+            5,  # Distance
+            [origin, [xy.Name + ".", xy.Name + "."]],
+            [body, [datum.Name + ".", datum.Name + "."]],
+        )
+        joint.Distance = 0.0
+
+        result = self.assembly.solve()
+        self.assertNotEqual(
+            result,
+            -1,
+            "Distance joint origin plane → PartDesign::Plane should not fail "
+            "(DistanceType should be PlanePlane, not Other)",
+        )

src/Mod/Assembly/CMakeLists.txt

@@ -60,6 +60,8 @@ SET(AssemblyTests_SRCS
     AssemblyTests/TestSolverIntegration.py
     AssemblyTests/TestKindredSolverIntegration.py
     AssemblyTests/TestKCSolvePy.py
+    AssemblyTests/TestAssemblyOriginPlanes.py
+    AssemblyTests/TestDatumClassification.py
     AssemblyTests/mocks/__init__.py
     AssemblyTests/mocks/MockGui.py
 )

src/Mod/Assembly/CommandCreateAssembly.py

@@ -22,15 +22,14 @@
 # **************************************************************************/
 
 import FreeCAD as App
-
 from PySide.QtCore import QT_TRANSLATE_NOOP
 
 if App.GuiUp:
     import FreeCADGui as Gui
     from PySide import QtCore, QtGui, QtWidgets
 
-import UtilsAssembly
 import Preferences
+import UtilsAssembly
 
 translate = App.Qt.translate
 
@@ -78,14 +77,22 @@ class CommandCreateAssembly:
                 'assembly = activeAssembly.newObject("Assembly::AssemblyObject", "Assembly")\n'
             )
         else:
-            commands = (
-                'assembly = App.ActiveDocument.addObject("Assembly::AssemblyObject", "Assembly")\n'
-            )
+            commands = 'assembly = App.ActiveDocument.addObject("Assembly::AssemblyObject", "Assembly")\n'
 
         commands = commands + 'assembly.Type = "Assembly"\n'
         commands = commands + 'assembly.newObject("Assembly::JointGroup", "Joints")'
 
         Gui.doCommand(commands)
+
+        # Make origin planes visible by default so they serve as
+        # reference geometry (like SolidWorks Front/Top/Right planes).
+        Gui.doCommandGui(
+            "assembly.Origin.ViewObject.Visibility = True\n"
+            "for feat in assembly.Origin.OriginFeatures:\n"
+            "    if feat.isDerivedFrom('App::Plane'):\n"
+            "        feat.ViewObject.Visibility = True\n"
+        )
+
         if not activeAssembly:
             Gui.doCommandGui("Gui.ActiveDocument.setEdit(assembly)")
 
@@ -98,7 +105,9 @@ class ActivateAssemblyTaskPanel:
     def __init__(self, assemblies):
         self.assemblies = assemblies
         self.form = QtWidgets.QWidget()
-        self.form.setWindowTitle(translate("Assembly_ActivateAssembly", "Activate Assembly"))
+        self.form.setWindowTitle(
+            translate("Assembly_ActivateAssembly", "Activate Assembly")
+        )
 
         layout = QtWidgets.QVBoxLayout(self.form)
         label = QtWidgets.QLabel(
@@ -132,9 +141,12 @@ class CommandActivateAssembly:
     def GetResources(self):
         return {
             "Pixmap": "Assembly_ActivateAssembly",
-            "MenuText": QT_TRANSLATE_NOOP("Assembly_ActivateAssembly", "Activate Assembly"),
+            "MenuText": QT_TRANSLATE_NOOP(
+                "Assembly_ActivateAssembly", "Activate Assembly"
+            ),
             "ToolTip": QT_TRANSLATE_NOOP(
-                "Assembly_ActivateAssembly", "Sets an assembly as the active one for editing."
+                "Assembly_ActivateAssembly",
+                "Sets an assembly as the active one for editing.",
             ),
             "CmdType": "ForEdit",
         }
@@ -156,7 +168,9 @@ class CommandActivateAssembly:
 
     def Activated(self):
         doc = App.ActiveDocument
-        assemblies = [o for o in doc.Objects if o.isDerivedFrom("Assembly::AssemblyObject")]
+        assemblies = [
+            o for o in doc.Objects if o.isDerivedFrom("Assembly::AssemblyObject")
+        ]
 
         if len(assemblies) == 1:
             # If there's only one, activate it directly without showing a dialog

src/Mod/Assembly/TestAssemblyWorkbench.py

@@ -22,6 +22,7 @@
 # **************************************************************************/
 
 import TestApp
+from AssemblyTests.TestAssemblyOriginPlanes import TestAssemblyOriginPlanes
 from AssemblyTests.TestCommandInsertLink import TestCommandInsertLink
 from AssemblyTests.TestCore import TestCore
 from AssemblyTests.TestKCSolvePy import (
@@ -36,5 +37,6 @@ from AssemblyTests.TestSolverIntegration import TestSolverIntegration
 # Use the modules so that code checkers don't complain (flake8)
 True if TestCore else False
 True if TestCommandInsertLink else False
+True if TestAssemblyOriginPlanes else False
 True if TestSolverIntegration else False
 True if TestKindredSolverIntegration else False

src/Mod/Create/CMakeLists.txt

@@ -85,6 +85,22 @@ install(
         mods/sdk
 )
 
+# Install QuickNav addon
+install(
+    DIRECTORY
+        ${CMAKE_SOURCE_DIR}/mods/quicknav/quicknav
+    DESTINATION
+        mods/quicknav
+)
+install(
+    FILES
+        ${CMAKE_SOURCE_DIR}/mods/quicknav/package.xml
+        ${CMAKE_SOURCE_DIR}/mods/quicknav/Init.py
+        ${CMAKE_SOURCE_DIR}/mods/quicknav/InitGui.py
+    DESTINATION
+        mods/quicknav
+)
+
 # Install Kindred Solver addon
 install(
     DIRECTORY

src/Mod/Create/kc_format.py

@@ -162,34 +162,28 @@ class _KcFormatObserver:
                     f"kc_format: pre_reinject hook failed: {exc}\n"
                 )
         try:
+            # Ensure silo/manifest.json exists in entries and update modified_at.
+            # All manifest mutations happen here so only one copy is written.
+            if "silo/manifest.json" in entries:
+                try:
+                    manifest = json.loads(entries["silo/manifest.json"])
+                except (json.JSONDecodeError, ValueError):
+                    manifest = _default_manifest()
+            else:
+                manifest = _default_manifest()
+            manifest["modified_at"] = datetime.now(timezone.utc).strftime(
+                "%Y-%m-%dT%H:%M:%SZ"
+            )
+            entries["silo/manifest.json"] = (
+                json.dumps(manifest, indent=2) + "\n"
+            ).encode("utf-8")
+
             with zipfile.ZipFile(filename, "a") as zf:
                 existing = set(zf.namelist())
-                # Re-inject cached silo/ entries
-                if entries:
-                    for name, data in entries.items():
-                        if name not in existing:
-                            zf.writestr(name, data)
-                            existing.add(name)
-                # Ensure silo/manifest.json exists
-                if "silo/manifest.json" not in existing:
-                    manifest = _default_manifest()
-                    zf.writestr(
-                        "silo/manifest.json",
-                        json.dumps(manifest, indent=2) + "\n",
-                    )
-                else:
-                    # Update modified_at timestamp
-                    raw = zf.read("silo/manifest.json")
-                    manifest = json.loads(raw)
-                    now = datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")
-                    if manifest.get("modified_at") != now:
-                        manifest["modified_at"] = now
-                        # ZipFile append mode can't overwrite; write new entry
-                        # (last duplicate wins in most ZIP readers)
-                        zf.writestr(
-                            "silo/manifest.json",
-                            json.dumps(manifest, indent=2) + "\n",
-                        )
+                for name, data in entries.items():
+                    if name not in existing:
+                        zf.writestr(name, data)
+                        existing.add(name)
         except Exception as e:
             FreeCAD.Console.PrintWarning(
                 f"kc_format: failed to update .kc silo/ entries: {e}\n"
@@ -209,17 +203,36 @@ def update_manifest_fields(filename, updates):
         return
     if not os.path.isfile(filename):
         return
+    import shutil
+    import tempfile
+
     try:
-        with zipfile.ZipFile(filename, "a") as zf:
-            if "silo/manifest.json" not in zf.namelist():
-                return
-            raw = zf.read("silo/manifest.json")
-            manifest = json.loads(raw)
-            manifest.update(updates)
-            zf.writestr(
-                "silo/manifest.json",
-                json.dumps(manifest, indent=2) + "\n",
-            )
+        fd, tmp = tempfile.mkstemp(suffix=".kc", dir=os.path.dirname(filename))
+        os.close(fd)
+        try:
+            with (
+                zipfile.ZipFile(filename, "r") as zin,
+                zipfile.ZipFile(tmp, "w", compression=zipfile.ZIP_DEFLATED) as zout,
+            ):
+                found = False
+                for item in zin.infolist():
+                    if item.filename == "silo/manifest.json":
+                        if found:
+                            continue  # skip duplicate entries
+                        found = True
+                        raw = zin.read(item.filename)
+                        manifest = json.loads(raw)
+                        manifest.update(updates)
+                        zout.writestr(
+                            item.filename,
+                            json.dumps(manifest, indent=2) + "\n",
+                        )
+                    else:
+                        zout.writestr(item, zin.read(item.filename))
+            shutil.move(tmp, filename)
+        except BaseException:
+            os.unlink(tmp)
+            raise
     except Exception as e:
         FreeCAD.Console.PrintWarning(f"kc_format: failed to update manifest: {e}\n")
 

tests/src/Base/UniqueNameManager.cpp

@@ -122,4 +122,15 @@ TEST(UniqueNameManager, UniqueNameWith9NDigits)
     manager.addExactName("Compound123456789");
     EXPECT_EQ(manager.makeUniqueName("Compound", 3), "Compound123456790");
 }
+TEST(UniqueNameManager, StructuredPartNumberDecomposition)
+{
+    // Structured part numbers like P03-0001 have their trailing digits
+    // treated as the uniquifying suffix by UniqueNameManager. This is
+    // correct for default FreeCAD objects (Body -> Body001) but wrong
+    // for structured identifiers. Assembly module handles this separately
+    // via makeInstanceLabel which appends -N instance suffixes instead.
+    Base::UniqueNameManager manager;
+    manager.addExactName("P03-0001");
+    EXPECT_EQ(manager.makeUniqueName("P03-0001", 3), "P03-0002");
+}
 // NOLINTEND(cppcoreguidelines-*,readability-*)

tests/test_kindred_pure.py

@@ -101,6 +101,7 @@ sys.path.insert(0, str(_REPO_ROOT / "src" / "Mod" / "Create"))
 sys.path.insert(0, str(_REPO_ROOT / "mods" / "sdk"))
 sys.path.insert(0, str(_REPO_ROOT / "mods" / "ztools" / "ztools"))
 sys.path.insert(0, str(_REPO_ROOT / "mods" / "silo" / "freecad"))
+sys.path.insert(0, str(_REPO_ROOT / "mods" / "quicknav"))
 
 # ---------------------------------------------------------------------------
 # Now import the modules under test
@@ -123,6 +124,15 @@ from silo_commands import _safe_float  # noqa: E402
 import silo_start  # noqa: E402
 import silo_origin  # noqa: E402
 
+from quicknav.workbench_map import (  # noqa: E402
+    WORKBENCH_SLOTS,
+    WORKBENCH_GROUPINGS,
+    get_workbench_slot,
+    get_groupings,
+    get_grouping,
+    get_command,
+)
+
 
 # ===================================================================
 # Test: update_checker._parse_version
@@ -554,6 +564,110 @@ class TestDatumModes(unittest.TestCase):
         self.assertEqual(len(points), 5)
 
 
+# ===================================================================
+# Test: quicknav workbench_map
+# ===================================================================
+
+
+class TestWorkbenchMap(unittest.TestCase):
+    """Tests for quicknav.workbench_map data and helpers."""
+
+    def test_all_slots_defined(self):
+        for n in range(1, 6):
+            slot = WORKBENCH_SLOTS.get(n)
+            self.assertIsNotNone(slot, f"Slot {n} missing from WORKBENCH_SLOTS")
+
+    def test_slot_keys(self):
+        for n, slot in WORKBENCH_SLOTS.items():
+            self.assertIn("key", slot)
+            self.assertIn("class_name", slot)
+            self.assertIn("display", slot)
+            self.assertIsInstance(slot["key"], str)
+            self.assertIsInstance(slot["class_name"], str)
+            self.assertIsInstance(slot["display"], str)
+
+    def test_each_slot_has_groupings(self):
+        for n, slot in WORKBENCH_SLOTS.items():
+            groupings = WORKBENCH_GROUPINGS.get(slot["key"])
+            self.assertIsNotNone(groupings, f"No groupings for workbench key '{slot['key']}'")
+            self.assertGreater(len(groupings), 0, f"Empty groupings for slot {n}")
+
+    def test_max_nine_groupings_per_workbench(self):
+        for wb_key, groupings in WORKBENCH_GROUPINGS.items():
+            self.assertLessEqual(len(groupings), 9, f"More than 9 groupings for '{wb_key}'")
+
+    def test_max_nine_commands_per_grouping(self):
+        for wb_key, groupings in WORKBENCH_GROUPINGS.items():
+            for i, grp in enumerate(groupings):
+                self.assertLessEqual(
+                    len(grp["commands"]),
+                    9,
+                    f"More than 9 commands in '{wb_key}' grouping {i}",
+                )
+
+    def test_command_tuples_are_str_str(self):
+        for wb_key, groupings in WORKBENCH_GROUPINGS.items():
+            for i, grp in enumerate(groupings):
+                self.assertIn("name", grp)
+                self.assertIn("commands", grp)
+                for j, cmd in enumerate(grp["commands"]):
+                    self.assertIsInstance(cmd, tuple, f"{wb_key}[{i}][{j}] not tuple")
+                    self.assertEqual(len(cmd), 2, f"{wb_key}[{i}][{j}] not length 2")
+                    self.assertIsInstance(cmd[0], str, f"{wb_key}[{i}][{j}][0] not str")
+                    self.assertIsInstance(cmd[1], str, f"{wb_key}[{i}][{j}][1] not str")
+
+    def test_get_workbench_slot_valid(self):
+        for n in range(1, 6):
+            slot = get_workbench_slot(n)
+            self.assertIsNotNone(slot)
+            self.assertEqual(slot, WORKBENCH_SLOTS[n])
+
+    def test_get_workbench_slot_invalid(self):
+        self.assertIsNone(get_workbench_slot(0))
+        self.assertIsNone(get_workbench_slot(6))
+        self.assertIsNone(get_workbench_slot(99))
+
+    def test_get_groupings_valid(self):
+        for slot in WORKBENCH_SLOTS.values():
+            result = get_groupings(slot["key"])
+            self.assertIsNotNone(result)
+            self.assertIsInstance(result, list)
+
+    def test_get_groupings_invalid(self):
+        self.assertEqual(get_groupings("nonexistent"), [])
+
+    def test_get_grouping_valid(self):
+        for wb_key, groupings in WORKBENCH_GROUPINGS.items():
+            for i in range(len(groupings)):
+                grp = get_grouping(wb_key, i)
+                self.assertIsNotNone(grp)
+                self.assertEqual(grp, groupings[i])
+
+    def test_get_grouping_invalid_index(self):
+        wb_key = WORKBENCH_SLOTS[1]["key"]
+        self.assertIsNone(get_grouping(wb_key, 99))
+        self.assertIsNone(get_grouping(wb_key, -1))
+
+    def test_get_grouping_invalid_key(self):
+        self.assertIsNone(get_grouping("nonexistent", 0))
+
+    def test_get_command_valid(self):
+        for wb_key, groupings in WORKBENCH_GROUPINGS.items():
+            for gi, grp in enumerate(groupings):
+                for ci in range(len(grp["commands"])):
+                    cmd_id = get_command(wb_key, gi, ci + 1)
+                    self.assertIsNotNone(cmd_id, f"None for {wb_key}[{gi}][{ci + 1}]")
+                    self.assertEqual(cmd_id, grp["commands"][ci][0])
+
+    def test_get_command_invalid_number(self):
+        wb_key = WORKBENCH_SLOTS[1]["key"]
+        self.assertIsNone(get_command(wb_key, 0, 0))
+        self.assertIsNone(get_command(wb_key, 0, 99))
+
+    def test_get_command_invalid_workbench(self):
+        self.assertIsNone(get_command("nonexistent", 0, 1))
+
+
 # ===================================================================