chore: add mypy strict type checking

.github/workflows/ci.yml

@@ -69,5 +69,8 @@ jobs:
       - name: Format check
         run: ruff format --check .
 
+      - name: Type check
+        run: mypy src/
+
       - name: Test
         run: pytest -v

pyproject.toml

@@ -33,6 +33,7 @@ dev = [
     "pytest",
     "pytest-asyncio",
     "ruff",
+    "mypy",
 ]
 
 [tool.ruff]
@@ -42,6 +43,19 @@ line-length = 100
 [tool.ruff.lint]
 select = ["E", "F", "I", "N", "W", "UP"]
 
+[tool.mypy]
+python_version = "3.11"
+strict = true
+warn_unused_ignores = true
+warn_redundant_casts = true
+warn_unreachable = true
+show_error_codes = true
+exclude = ["build/", "dist/"]
+
+[[tool.mypy.overrides]]
+module = "tests.*"
+disallow_untyped_defs = false
+
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
 testpaths = ["tests"]

src/my_mcp_server/server.py

@@ -33,13 +33,13 @@
 # ---------------------------------------------------------------------------
 
 
-def ok(data: str | dict) -> dict:
+def ok(data: str | dict[str, object]) -> dict[str, object]:
     """Return a successful tool response."""
     text = data if isinstance(data, str) else str(data)
     return {"content": [{"type": "text", "text": text}]}
 
 
-def err(message: str) -> dict:
+def err(message: str) -> dict[str, object]:
     """Return an error tool response."""
     return {"content": [{"type": "text", "text": message}], "isError": True}