feat(recall): add metadata sidecar search

[jack-arturo]

Summary

• Add a bounded evidence-based metadata sidecar candidate channel to /recall, controlled by RECALL_METADATA_SEARCH_ENABLED.
• Search whitelisted metadata values without replacing content vectors, generating production tags, mutating graph content, or changing the HTTP API.
• Use field words only for scoring/disambiguation; this is not keyword-intent routing.
• Document metadata storage, recall response shape, update/enrichment behavior, consolidation notes, and search behavior for issue End-to-end metadata audit: storage, consolidation, search, and recall #110.

Breaking Changes

None.

Validation

• .venv/bin/python -m pytest -q -> 465 passed, 12 skipped.
• Real-data eval: data/sweep_runs/20260610T174320Z-metadata-server-metadata-search.
• Metadata hit@5: 0.140 -> 0.770; MRR: 0.126 -> 0.672.
• Qdrant vectors stayed byte-identical: 9,921 baseline and 9,921 candidate vectors.
• Preserve/mixed suite had zero non-OK statuses.

Eval harness PR: verygoodplugins/automem-evals#10

Closes #110

[Copilot]

Pull request overview

Adds a bounded “metadata sidecar” candidate channel to /recall, allowing recall ranking to consider whitelisted memory metadata values (without mutating stored vectors/content) and documenting the end-to-end metadata behavior.

Changes:

• Introduces graph-side metadata candidate search and wires it into recall behind RECALL_METADATA_SEARCH_ENABLED.
• Extends scoring to account for match_type="metadata" via SEARCH_WEIGHT_METADATA.
• Adds tests and documentation for metadata lifecycle and recall-side behavior.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/test_metadata_recall_search.py	Adds coverage for metadata sidecar admission, whitelisting rules, and scoring behavior.
docs/METADATA_BEHAVIOR.md	Documents current metadata storage/recall/update/enrichment/consolidation behavior and new sidecar search rules.
docs/ENVIRONMENT_VARIABLES.md	Documents RECALL_METADATA_SEARCH_ENABLED env var for enabling/disabling the sidecar channel.
docs/API.md	Notes metadata sidecar recall behavior and the controlling env var.
automem/utils/scoring.py	Adds a metadata score component and includes it in final scoring.
automem/search/runtime_recall_helpers.py	Implements metadata parsing/tokenization/matching and graph query for metadata sidecar candidates.
automem/runtime_wiring.py	Wires the metadata search function into blueprint registration.
automem/config.py	Adds RECALL_METADATA_SEARCH_ENABLED and SEARCH_WEIGHT_METADATA configuration.
automem/api/runtime_recall_routes.py	Passes the metadata search function through the runtime recall route DI.
automem/api/runtime_bootstrap.py	Threads metadata search function into blueprint registration.
automem/api/recall.py	Runs metadata sidecar search during recall and incorporates results into scoring/ranking.
app.py	Exposes _metadata_keyword_search as a runtime attribute for wiring.