feat(collection): task #61 P1-D3 — vector backend identity + capability matrix

[earayu]

Summary

Project the deployment-wide settings.vector_db_type onto every collection detail read so the FE can render a "what does this vector backend actually support" panel without per-collection migration or runtime probe.

• Backend (output-only projection): new VectorBackendCapabilities + VectorBackendInfo + projection helper + Collection.vector_backend field + build_collection_response populates it.
• Cross-PR consistency with task feat: support on premise deployment #83 / PR feat(vectorstore): task #61 P1-V vector adapter family — capability + filter Or guard + retrieve defense-in-depth #1948 (Bryce, vector adapter behavior fixes): mirrors BACKEND_CAPABILITIES ClassVar truth values; uniform-False on supports_filter_or_with_empty_parts after task feat: support on premise deployment #83 P1-V3 reject-on-both-translators.
• Mechanical gate (Lesson feat: auto size for chat input #18 lesson-sediment + mechanical-gate codification): 13-case unit suite pins each capability flag, normalizes inputs, round-trips Pydantic.
• FE: typed mirrors + CollectionVectorBackendCard component on the settings page (above the edit form). dongdong picks up rendering polish (responsive + dark mode + final copy) on the same PR per the joint A4-style split (cuiwenbo contract layer + dongdong rendering polish + CR pair).

Schema-placement decision (per architect msg=0044261f + dongdong msg=c2593fdd + PM msg=caf7e4df): vector_backend is on Collection (read response only), NOT on CollectionConfig (input shape) — this prevents callers from mistaking a deployment-wide setting for a per-collection editable knob.

Spec / sediment cites:

• docs/zh-CN/architecture/task-61-db-adapter-compat-spec-v1.md § 2.3 P1-D3
• Lesson feat: chat #17 backend 收敛 contract simple-stable family (cite PR feat(vectorstore): cross-adapter filter fail-loud + score normalization (task #61 P0-A + P0-B) #1930 score normalize, PR feat(graph-curation): task #31 A2 suggestion status schema #1935 GraphMergeSuggestionItem projection layer)
• Lesson feat: auto size for chat input #18 lesson-sediment + mechanical-gate 双 layer codification (cite PR test(task-33-p3): cross-source default value gate for graph_extraction_window_size #1933 / PR refactor(task-31-a3): description-free graph_curation 7 call sites #1941 / PR feat(graph): task #31 A4 merge suggestion UI #1940 mechanical-gate boundary tests)
• mini-pattern 19 layer 4 (cuiwenbo own-up grep main on graph_backend_type per-collection vs vector_db_type deployment-wide divergence; architect lock Option B per spec § 2.3 P1-D3 read-only projection)

Test plan

• uv run --extra test pytest tests/unit_test/contracts/test_vector_backend_capability_matrix.py tests/unit_test/contracts/test_collection_v2_openapi_contract.py -q → 23 passed
• make openapi-check → ok
• yarn type-check --pretty false → 0 new errors on this PR's files
• yarn lint --quiet → 0 warnings/errors
• yarn i18n:check → ok
• git diff --check → ok
• CR pair @dongdong rendering polish + final pass
• CR @符炫炜 ratify
• CR @weston framing verify
• CI all green

🤖 Generated with Claude Code

[earayu]

Testing final pass ✅

I rechecked the 2515918 fix-forward from the contract side:

• vector_backend is now a Pydantic @computed_field, so generated OpenAPI splits correctly:
  • Collection-Output has readonly vector_backend: VectorBackendInfo | null
  • Collection-Input has no vector_backend
  • CollectionCreate / CollectionUpdate have no vector_backend
  • Agent-Input.collections and CreateTurnRequest.collections both reference Collection-Input, so request-side schemas stay clean
• Capability matrix still matches the task feat: support on premise deployment #83 / PR feat(vectorstore): task #61 P1-V vector adapter family — capability + filter Or guard + retrieve defense-in-depth #1948 behavior contract:
  • pgvector: atomic batch upsert true, empty-Or false, legacy mode false
  • qdrant: atomic batch upsert false, empty-Or false, legacy mode true
• The new contract tests cover the computed-field input/output split and ignored malicious input payload path.

Local targeted validation:

uv run --extra test pytest tests/unit_test/contracts/test_vector_backend_capability_matrix.py tests/unit_test/contracts/test_collection_v2_openapi_contract.py -q
# 25 passed

make openapi-check
# passed

git diff --check origin/main...HEAD
# passed

I could not rerun FE yarn type-check / yarn lint in my temp worktree because web/node_modules is absent there (tsc / next not found). @dongdong has separately run the FE checks on the same fix-forward and reported them green, so my testing lane has no remaining blocker.