Add comprehensive tests for vector/semantic search functionality

- Implement full coverage tests for Embedder model loading and embedding generation
- Add CRUD operations and caching tests for VectorStore
- Include cosine similarity computation tests
- Validate semantic search accuracy and relevance through various queries
- Establish performance benchmarks for embedding and search operations
- Ensure edge cases and error handling are covered
- Test thread safety and concurrent access scenarios
- Verify availability of semantic search dependencies

.claude/rules/tool-selection.md

@@ -0,0 +1,88 @@
+# Tool Selection Rules
+
+## Context Gathering
+
+### Use Exa
+- Researching external APIs, libraries, frameworks
+- Need recent documentation beyond knowledge cutoff
+- Looking for implementation examples in public repos
+- User mentions specific library/framework names
+- Questions about "best practices" or "how does X work"
+
+### Use read_file (MCP)
+- Reading multiple related files at once
+- Directory traversal with pattern matching
+- Searching file content with regex
+- Need to limit depth/file count for large directories
+- Batch operations on multiple files
+- Pattern-based filtering (glob + content regex)
+
+### Use codex_lens
+- Large codebase (>500 files) requiring repeated searches
+- Need semantic understanding of code relationships
+- Working across multiple sessions
+- Symbol-level navigation needed
+- Finding all implementations of interface/class
+- Tracking function calls across codebase
+
+### Use smart_search
+- Unknown file locations
+- Concept/semantic search ("authentication logic", "payment processing")
+- Medium-sized codebase (100-500 files)
+- One-time or infrequent searches
+- Natural language queries about code structure
+
+**Mode Selection**:
+- `auto`: Let tool decide (default)
+- `exact`: Known exact pattern
+- `fuzzy`: Typo-tolerant search
+- `semantic`: Concept-based search
+- `graph`: Dependency analysis
+
+## File Modification
+
+### Use edit_file (MCP)
+- Built-in Edit tool failed 1+ times
+- Need dry-run preview before applying changes
+- Need line-based operations (insert_after, insert_before)
+- Need to replace all occurrences at once
+- Built-in Edit returns "old_string not found"
+- Whitespace/formatting issues in built-in Edit
+
+**Mode Selection**:
+- `mode=update`: Replace text
+- `mode=line`: Line-based operations
+
+### Use write_file (MCP)
+- Creating brand new files
+- MCP edit_file still fails (last resort)
+- Need to completely replace file content
+- Need backup before overwriting
+- User explicitly asks to "recreate file"
+
+## Priority Logic
+
+**File Reading**:
+1. Known single file → Built-in Read
+2. Multiple files OR pattern matching → read_file (MCP)
+3. Unknown location → smart_search then Read
+4. Large codebase + repeated access → codex_lens
+
+**File Editing**:
+1. Always try built-in Edit first
+2. Fails 1+ times → edit_file (MCP)
+3. Still fails → write_file (MCP)
+
+**Search**:
+1. External knowledge → Exa
+2. Exact pattern in small codebase → Built-in Grep
+3. Semantic/unknown location → smart_search
+4. Large codebase + repeated searches → codex_lens
+
+## Decision Triggers
+
+**Start with simplest tool** (Read, Edit, Grep)
+**Escalate to MCP tools** when built-ins fail or inappropriate
+**Use semantic search** for exploratory tasks
+**Use indexed search** for large, stable codebases
+**Use Exa** for external/public knowledge