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Issue #29 Implementation Doc Stub

1. Issue reference

  • GitHub issue: #29
  • Issue title: [Backend][Retrieval] 75/25 hybrid search with RRF + BM25 fusion
  • Issue type: feature
  • Milestone: Backend RAG M3 - Retrieval & Chat Quality

2. Summary

  • What this issue changed: TBD
  • Why the change was needed: implement the target hybrid retrieval strategy for stronger recall and ranking.

3. Initial repo state

  • Relevant behavior before implementation: the repo already includes a global hybrid retrieval plan and related documentation, but this issue is still pending.
  • Known constraints or gaps at start: weighting, RRF details, and lexical search contract must stay aligned with the chosen plan.

4. Plan doc referenced

  • Plan doc path: docs/plans/2026-02-21-global-retrieval-hybrid-rrf-implementation.md
  • Plan status at implementation start: Draft / For Review
  • Was the plan updated during implementation?: TBD
  • If yes, what changed in the plan?: TBD

5. Decisions taken

Decision Reason Alternative rejected
Stub only Pre-create the execution record for a retrieval issue with multiple moving parts. Leaving implementation details spread across PR notes and ops docs.

6. Files changed

File Change summary
docs/implementation/issue-29-hybrid-search-rrf-bm25-fusion.md Created implementation doc stub.

7. Migrations / schema changes

  • Migration files: none yet
  • Schema changes: none yet
  • Data backfill or manual steps: none yet
  • Rollback notes: not applicable yet

8. API changes

Surface Change Compatibility impact
None yet No implementation details recorded yet. None

9. Tests added or updated

Test file or suite Change
None yet No implementation work has started.

10. Risks / caveats

  • Retrieval changes are system-wide and can affect correctness, latency, and cost if the plan drifts.

11. Follow-up work

  • Update the plan doc if weighting or ranking behavior changes during implementation.
  • Record migrations, search contract changes, and benchmark results when work begins.

12. Final repo state

  • Relevant behavior after implementation: not implemented yet; stub created to reserve the issue record.
  • Remaining limitations: retrieval implementation and validation are pending.

13. Docs updated

Doc path Update summary
docs/implementation/issue-29-hybrid-search-rrf-bm25-fusion.md Added initial implementation doc stub.