## ADDED Requirements

### Requirement: Hybrid search with vector + keyword fusion
The system SHALL combine vector similarity search and keyword search into unified ranked results.

#### Scenario: Vector search runs when embedding provider available
- **WHEN** an embedding provider is configured
- **THEN** the system SHALL compute a query embedding and perform cosine similarity search
- **WHEN** no embedding provider is configured
- **THEN** the system SHALL gracefully degrade to keyword-only search

#### Scenario: Keyword search always runs
- **WHEN** a search query is submitted
- **THEN** the system SHALL always perform keyword search regardless of embedding provider availability

#### Scenario: Weighted score merging
- **WHEN** both vector and keyword results are available
- **THEN** the final score SHALL be: `vector_weight * vector_score + keyword_weight * keyword_score`
- **THEN** default weights SHALL be `vector_weight=0.7`, `keyword_weight=0.3`
- **THEN** weights SHALL be configurable

### Requirement: Vector search via numpy cosine similarity
The system SHALL perform vector search using numpy-vectorized cosine similarity for performance.

#### Scenario: Vectorized cosine similarity
- **WHEN** numpy is available
- **THEN** all chunk embeddings SHALL be loaded into a numpy matrix `(N, D)`
- **THEN** cosine similarity SHALL be computed as `matrix @ query_vector` (BLAS matrix-vector multiply)
- **THEN** top-K results SHALL be selected via `argpartition` (O(N) average)

#### Scenario: Pure-Python fallback
- **WHEN** numpy is unavailable
- **THEN** cosine similarity SHALL be computed per-row with pure Python
- **THEN** results SHALL be sorted and the top K returned

### Requirement: Three-tier keyword search (FTS5 → trigram → LIKE)
The system SHALL provide a cascading keyword search strategy for multi-language support.

#### Scenario: Standard FTS5 for ASCII queries
- **WHEN** the query contains only ASCII characters
- **THEN** the system SHALL use SQLite FTS5 with the unicode61 tokenizer
- **THEN** BM25 ranking SHALL be converted to a `[0, 1)` score

#### Scenario: Trigram FTS5 for CJK queries
- **WHEN** the query contains CJK (Chinese, Japanese, Korean) characters
- **THEN** the system SHALL use SQLite FTS5 with the trigram tokenizer
- **THEN** CJK character sequences and ASCII words SHALL be extracted and joined with AND

#### Scenario: LIKE fallback for edge cases
- **WHEN** FTS5 is unavailable or returns empty results
- **THEN** the system SHALL fall back to LIKE-based search
- **THEN** CJK runs (1+ chars) and ASCII words (3+ chars) SHALL be matched independently

### Requirement: Temporal decay for dated memory files
The system SHALL apply exponential decay to search scores for dated memory files.

#### Scenario: Decay applied to dated files
- **WHEN** a memory chunk path matches `YYYY-MM-DD.md`
- **THEN** the combined score SHALL be multiplied by `exp(-ln(2)/half_life * age_days)`
- **THEN** the default `half_life` SHALL be 30 days
- **WHEN** the path does not contain a date (e.g., `MEMORY.md`)
- **THEN** no decay SHALL be applied (multiplier = 1.0)

### Requirement: Result filtering and limits
The system SHALL filter search results by minimum score and maximum count.

#### Scenario: Min score threshold
- **WHEN** search results are merged
- **THEN** results with score below `min_score` (default 0.1) SHALL be discarded

#### Scenario: Max results limit
- **WHEN** search results exceed `max_results`
- **THEN** only the top `max_results` by combined score SHALL be returned