Implements issue #142 — .kc checkout pipeline that repacks silo/ entries
with current DB state before serving downloads.
When a client downloads a .kc file via GET /api/items/{pn}/file/{rev},
the server now:
1. Reads the file from storage into memory
2. Checks for silo/ directory (plain .fcstd files bypass packing)
3. Repacks silo/ entries with current item_metadata + revision history
4. Streams the repacked ZIP to the client
New files:
- internal/kc/pack.go: Pack() replaces silo/ entries in ZIP, preserving
all non-silo entries (FreeCAD files, thumbnails) with original
compression and timestamps. HasSiloDir() for lightweight detection.
- internal/api/pack_handlers.go: packKCFile server helper, computeETag,
canSkipRepack lazy optimization.
ETag caching:
- ETag computed from revision_number + metadata.updated_at
- If-None-Match support returns 304 Not Modified before reading storage
- Cache-Control: private, must-revalidate
Lazy packing optimization:
- Skips repack if revision_hash matches and metadata unchanged since upload
Phase 2 packs: manifest.json, metadata.json, history.json,
dependencies.json (empty []). Approvals, macros, jobs deferred to
Phase 3-5.
Closes#142
c216d64702