port(omniroute): add configurable embedding and hybrid memory retrieval #1125

Outcome

Complete retrieval only after the memory contract exists. Reuse existing embeddings/rerank providers instead of inventing a separate credential store.

Evidence and source state

DurinDoor baseline: 93f6de64c69b17d52f790d6f14d09a74cffc7fa5.

• src/sse/handlers/embeddings.js
  OmniRoute source snapshot: 61e07fb7e0d4e1e76111495d3718c9e4d06d2a62 on release/v3.8.52.
• src/lib/memory/embedding
• omniroute #2439: feat(memory): wire createMemory to upsertSemanticMemoryPoint (Qdrant) | MERGED | merge d42161566d552355a05ae8b66d2351602375d6d4
• omniroute #14427: fix: keep Qdrant embedding options limited to configured providers | MERGED | merge c9a5705440e5cbe322218ad69c7b8e0718fce31b

Implementation subtasks and acceptance criteria

• Select embedding/rerank models only from configured eligible providers.
• Version vector dimensions and reindex safely on model change.
• Evaluate relevance, token budget, failure fallback and key isolation.

Dependencies

• port(omniroute): add optional persistent memory with caller isolation #1124

Parent epic: #1065. Roadmap: #1056. Priority P3. Stage 4.

Delivery contract

Planning ticket only. No implementation, runtime test, live-provider call, deployment or stored-data mutation was performed in this audit. Before a port, confirm a merged final upstream diff or a reachable source commit, compare local equivalents/tests, and preserve local auth/routing/quota/database contracts. Open upstream work remains a review candidate. Use port(omniroute): title and target a focused PR at bloodf/durindoor:main. Behavior changes require a focused test plus docs. Run npm run lint and cd tests && npm run test:ci; never add baseline failures. Pure docs/CI edits may skip runtime tests. Regenerate registry/agent indexes with their scripts. Preserve stored credentials and unrelated work.