# Embedding Model Validation & Search Robustness

## Context
pgvector supports max 2000 dimensions for HNSW/IVFFlat indexes. The app must validate embedding models and gracefully handle dimension mismatches.

## Tasks

### 1. Revert dimension from 2560 back to 1536
- All files changed in commit e09ea3a need reverting: 1536 everywhere
- This includes: schema.prisma (both), migration.sql, embedding.service.ts, validate route, scripts, tests

### 2. Add embedding dimension validation in admin settings
File: `memento-note/lib/ai/services/embedding.service.ts`
- After generating an embedding, check its dimension
- Add a method `validateEmbeddingModel()` that:
  - Generates a test embedding
  - Checks dimension count
  - Returns { valid: boolean, dimensions: number, warning?: string }
  - If dimensions > 2000: warning "This model produces {N} dimensions. pgvector indexes support max 2000 dimensions. Semantic search will use sequential scan (slower for large note collections)."
  - If dimensions != current DB vector dimension: warning "Dimension mismatch: model produces {N}d but DB stores {M}d. You need to reindex all notes."

File: `memento-note/app/api/admin/embeddings/validate/route.ts`  
- Use the new validateEmbeddingModel() method
- Return dimension info in the API response

File: `memento-note/app/api/admin/settings/route.ts` (or wherever embedding model is saved)
- After saving a new embedding model, call validateEmbeddingModel()
- Store the warning in the response so the frontend can display it

### 3. Make semantic search robust
File: `memento-note/lib/ai/services/semantic-search.service.ts`
- In `vectorSearch()`: after generating query embedding, check dimension matches DB (1536). If not, log warning and return [] (fallback to FTS)
- In `_doSearch()`: the existing try/catch already calls `_ftsFallback()`. Make sure this works.

### 4. Update the migration SQL
File: `memento-note/prisma/migrations/20260512120000_pgvector_and_fts_search/migration.sql`
- Keep vector(1536) as the target type
- The migration should work correctly

### 5. Commit
- Git add and commit with descriptive message
- Do NOT push