fix: hybrid retrieval graceful degradation with Promise.allSettled

[ether-btc]

Bug 3: Hybrid Promise.all no fallback

Reported in community code audit

Problem

In , runs and in parallel. If either throws (e.g., FTS index corruption for BM25), the entire hybrid search fails — vector results are lost with no graceful degradation.

Fix

Replace with :

• One search fails → the other search's results are returned; failed side gets empty array + logged
• Both fail → throws with (preserves existing error telemetry)
• Diagnostics → / correctly show for failed searches

Testing

• TypeScript compiles cleanly (0 new errors in retriever.ts)
• Reviewed by Staff Engineer: APPROVED
• handles mixed + valid array correctly (BM25-only branch: , )

Files changed

• : method (+32/-7 lines)

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Audit reference: memory-lancedb-pro code audit — Bug 3, reported 2026-04-11

[rwmjhb]

Thanks for the fix — switching to Promise.allSettled is the right approach here. One blocking issue to address before merge:

Must Fix

F1 — Both-fail guard triggers on legitimate zero-result queries (src/retriever.ts:954)

// Current (incorrect)
if (vectorResults.length === 0 && bm25Results.length === 0) {
  throw attachFailureStage(new Error('both vector and BM25 search failed'), ...)
}

This condition fires when both backends succeed but return no matches — any sparse knowledge base or narrow query now throws "both vector and BM25 search failed" instead of returning []. It also masks single-backend failures: if one rejects and the other legitimately returns [], the wrong branch fires.

Fix: guard on settled status, not array length:

if (vectorResult_.status === 'rejected' && bm25Result_.status === 'rejected') {
  throw attachFailureStage(new Error('both vector and BM25 search failed'), ...)
}

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Nice to Have

• F2 (src/retriever.ts:955): The both-fail path discards original error context — vectorResult_.reason and bm25Result_.reason are console.warn'd but not propagated into the thrown error. Consider AggregateError([vectorResult_.reason, bm25Result_.reason], 'both searches failed') or embedding .message strings directly, so on-call diagnostics show why each backend failed.

• EF2: None of the three new degradation branches (vector-fail, BM25-fail, both-fail) are covered by tests. The F1 regression in particular can't be caught by the existing test suite. Worth adding a test that injects a rejected backend alongside an empty-result fulfilled backend.

• EF4: Base is stale — please rebase on current main before merge. src/retriever.ts is a high-risk module with active concurrent changes.

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Overall direction is good — this is worth merging once the length-vs-status guard is corrected.