Add long-term memory retrieval powered by qmd (BM25 and VSearch).

[mczabca-boop]

PR Title

Improve QMD Memory Retrieval Reliability, Observability, and Claude Injection Safety

Summary

This PR hardens TinyClaw’s memory pipeline end-to-end and removes several reliability pitfalls found during real Telegram regression testing.

It keeps memory retrieval QMD-centric (BM25 + VSearch), improves retrieval quality and debug visibility, and fixes the critical issue where memory snippets were retrieved but not reliably consumed by Claude.

Why

Memory behavior was inconsistent in production-like tests due to:

• semantic hits returning noisy/self-referential snippets
• stale/low-confidence snippets polluting final answers
• path normalization mismatches preventing turn hydration/reranking
• memory being injected into a file Claude CLI did not reliably consume
• potential cleanup overwrite risk when restoring CLAUDE.md
• high VSearch overhead from synchronous embed timing

This PR addresses those issues while preserving optional memory and safe defaults.

Key Changes

1. QMD retrieval flow hardening

• Retained QMD-only retrieval path:
  • BM25 (qmd search)
  • VSearch (qmd vsearch)
• Added stronger fallback behavior:
  • if VSearch results are filtered to unusable snippets, fallback to BM25
• Reused lexical query variants across precheck/main BM25 flow to avoid redundant recomputation.

2. Reranking and snippet quality improvements

• Moved rerank heuristics into a dedicated module:
  • src/lib/memory-rerank.ts
• Added configurable rerank settings under memory.rerank.
• Added stronger low-confidence filtering:
  • low-confidence assistant snippets are now filtered out from injection (not only downranked).
• Added rerank debug output to inspect top selected snippets in logs.

3. Turn hydration bug fixes

• Fixed source-to-turn-file resolution robustness:
  • handles qmd source normalization differences (case/punctuation variants like _ vs -)
• Standardized newly persisted turn filenames to lowercase to reduce future mismatch risk.
• Result: rerank/hydration can reliably use full User/Assistant turn content instead of raw patch-like snippets.

4. Claude memory injection redesign

• Replaced runtime injection target:
  • from .claude/MEMORY.md
  • to .claude/CLAUDE.md runtime section
• Added safer cleanup strategy:
  • inject with unique start/end markers
  • cleanup removes only marker-bounded runtime block
  • avoids full-file rollback overwrite risk when file changes during invocation
• Retained defensive cleanup for legacy MEMORY.md.

5. Embed/update behavior and latency improvements

• Increased default embed interval to reduce runtime overhead:
  • default embed_interval_seconds: 600
• Changed embed trigger to asynchronous fire-and-forget (non-blocking query path).
• Added in-flight guard per collection to avoid duplicate embed runs.

6. Logging and observability

• Added/kept clearer memory-source logs:
  • qmd-bm25 / qmd-vsearch
• Added injection-path logs.
• Added optional debug logging for:
  • mode, timeout, query-used, rerank summary, fallback behavior.
• Improved warning behavior to be agent-scoped instead of process-global for qmd-unavailable cases.

7. Configuration/setup/docs updates

• Setup wizard wording keeps VSearch explicitly marked as experimental:
  • Use semantic search (vector, experimental)? [y/N]
• Updated setup defaults and README to reflect:
  • safer semantic behavior
  • async embed behavior
  • longer embed interval
  • retention/rerank controls
  • memory source observability.

Validation Performed

• npm run build:main passed after changes.
• bash -n lib/setup-wizard.sh passed.
• End-to-end Telegram regressions validated:
  • correct memory source logs (qmd-vsearch, qmd-bm25 where applicable)
  • runtime injection log now shows .claude/CLAUDE.md (runtime section)
  • previously failing case (Who likes rock?) now correctly answers from retrieved memory after injection fix
  • repeated reset does not wipe persisted QMD memory (session reset behavior preserved).

Backward Compatibility

• Memory remains optional.
• TinyClaw still runs without qmd/bun; memory retrieval degrades gracefully when unavailable.
• Existing deployments continue to work; behavior is now more explicit and debuggable.

Notes / Reviewer Focus

Please focus review on:

• src/lib/memory.ts retrieval flow + fallback + hydration/rerank
• src/lib/memory-rerank.ts configuration-driven heuristics
• src/lib/invoke.ts marker-based CLAUDE.md runtime injection/cleanup safety
• setup/README defaults and wording around experimental semantic search.