feat(semantic): hybrid search + temporal decay for memory#27
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Add TemporalDecayConfig with exponential decay formula: score *= exp(-ln(2) / halflife * age_days) At age=0, multiplier=1.0. At age=halflife, multiplier=0.5. Handles edge cases: negative age, empty/unparseable dates, NaN/Inf protection.
Add --decay and --decay-half-life flags to memory search command. Add decay/decay_half_life properties to MCP memory_search tool. Decay is applied after search results, then re-sorted by score.
Create memory_fts virtual table with porter unicode61 tokenizer, indexing question + answer columns. Add INSERT/UPDATE/DELETE triggers for automatic sync. Add backfill for migration from pre-FTS databases. Wire into initSchema().
Implement MemoryLexicalSearcher interface on SQLiteStorage. Searches memory_fts (question + answer) with BM25 scoring, supports status/source/tag filtering. Converts BM25 scores to positive scale matching vector search convention.
Add FuseRRFMemory, FuseRRFMemoryWithTopK, FuseWeightedMemory for combining dense and lexical memory search results. Same algorithms as chunk-based fusion, keyed by Entry.ID.
Combines dense (cosine) + lexical (BM25) memory search with RRF or weighted fusion. Supports optional temporal decay. Over-fetches for better fusion quality, then applies topK. Gracefully degrades to dense-only if lexical search fails.
Add --hybrid flag to memory search command. When enabled, uses HybridSearchMemory (dense + lexical BM25 with RRF fusion). Decay works with both hybrid and dense-only modes. Add hybrid property to MCP memory_search tool schema.
- Validate decay-half-life before use (prevent div-by-zero with 0) - Apply temporal decay before topK truncation for correct ranking - Add COALESCE to chunk FTS5 backfill name column - Replace custom contains() with strings.Contains
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Summary
Hybrid Memory Search
memory_ftsvirtual table withporter unicode61tokenizer indexing question + answerLexicalSearchMemory()with BM25 scoring, tag/status/source filteringFuseRRFMemory()andFuseWeightedMemory()for result fusionHybridSearchMemory()orchestration: dense + lexical → RRF fusion → optional decay → topK--hybrid(CLI),hybrid(MCP)Temporal Decay
score *= exp(-ln(2) / halflife * age_days)--decay,--decay-half-life(CLI),decay,decay_half_life(MCP)MCP Token Trimming
json/minparams (handlers force these)storage/collection/profile/configfrom auto-profile semantic toolsTest plan
go test -run "^Test[^Q]" ./internal/semantic/...— all passgo test ./internal/semantic/commands/...— all passgo test ./internal/semantic/mcpserver/...— all pass