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docs/type-checking.md

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+# Type Checking
+
+Catch type mismatches at analysis time, not at runtime. Especially valuable in large codebases and across refactors.
+
+## Tools by Language
+
+| Language | Tool | Notes |
+|---|---|---|
+| Python | `mypy`, `pyright` | not built-in; add type hints manually |
+| JavaScript/TS | `tsc`, `flow` | TypeScript is the dominant choice |
+| Go | built-in | the compiler enforces types |
+| C++ | built-in + `clang-tidy` | compiler + static analysis |
+
+## Python — `mypy`
+
+```bash
+mypy src/
+```
+
+Configure in `pyproject.toml`:
+
+```toml
+[tool.mypy]
+python_version = "3.12"
+strict = true
+ignore_missing_imports = true
+```
+
+Start with `strict = false` and tighten incrementally. Add `# type: ignore` sparingly — only where third-party stubs are missing.
+
+## TypeScript — `tsc`
+
+```bash
+tsc --noEmit        # type-check without emitting JS
+```
+
+`tsconfig.json`:
+
+```json
+{
+  "compilerOptions": {
+    "strict": true,
+    "noEmit": true,
+    "target": "ES2022"
+  }
+}
+```
+
+## Tips
+
+- Type checking and linting are separate concerns — run both
+- In Python, annotate function signatures first; body annotations add less value
+- `pyright` (Pylance) gives faster feedback in VS Code; `mypy` is CI-standard