- SymbolExtractor protocol + SymbolSpan dataclass
- AstSymbolExtractor for Python (stdlib ast, no tree-sitter dep — KTD1)
- RegexSymbolExtractor for TS/JS/Go/Rust/Java (language-aware regex)
- ReadFileTool with path/symbol/start_line/end_line params
- symbol=None returns full file (characterization baseline matching _FakeTool)
- symbol='foo' returns first matching symbol's line range
- symbol not found returns available_symbols list (soft error)
- Unsupported extension returns full file with note
- Manual start_line/end_line overrides symbol
- 66 unit tests covering R22/R23 + characterization + edge cases
chiguyong