chore: add development tooling (ruff, mypy, pre-commit)

Author: future-xy

pyproject.toml

@@ -46,6 +46,9 @@ Issues = "https://github.com/ServerlessLLM/pylet/issues"
 dev = [
     "pytest>=7.0.0",
     "pytest-asyncio>=0.21.0",
+    "ruff>=0.8.0",
+    "mypy>=1.14.0",
+    "pre-commit>=4.0.0",
 ]
 
 [project.scripts]
@@ -60,4 +63,60 @@ asyncio_default_fixture_loop_scope = "function"
 testpaths = ["tests"]
 python_files = ["test_*.py"]
 python_classes = ["Test*"]
-python_functions = ["test_*"]
+python_functions = ["test_*"]
+
+[tool.ruff]
+target-version = "py39"
+line-length = 100
+src = ["pylet", "tests"]
+
+[tool.ruff.lint]
+select = [
+    "E",      # pycodestyle errors
+    "W",      # pycodestyle warnings
+    "F",      # pyflakes
+    "I",      # isort
+    "UP",     # pyupgrade
+    "B",      # flake8-bugbear
+    "SIM",    # flake8-simplify
+    "RUF",    # ruff-specific rules
+]
+ignore = [
+    "E501",   # line too long (handled by formatter)
+    "B008",   # do not perform function calls in argument defaults (needed for FastAPI Depends)
+    "B904",   # raise from err (HTTP exceptions don't need chains)
+    "RUF022", # __all__ not sorted (intentionally grouped by category)
+    "SIM102", # nested if statements (sometimes clearer)
+    "SIM105", # use contextlib.suppress (style preference)
+    "SIM115", # use context manager for open (not always possible)
+    "SIM117", # use single with statement (nested sometimes clearer)
+    "UP035",  # typing.X deprecated (need Optional, Union for Python 3.9 compat)
+]
+
+[tool.ruff.lint.isort]
+known-first-party = ["pylet"]
+
+[tool.mypy]
+python_version = "3.9"
+warn_return_any = false
+warn_unused_ignores = true
+disallow_untyped_defs = false
+check_untyped_defs = true
+ignore_missing_imports = true
+strict_optional = true
+files = ["pylet"]
+exclude = ["tests"]
+
+# Per-module overrides for stricter checking on core modules
+[[tool.mypy.overrides]]
+module = "pylet.schemas"
+disallow_untyped_defs = true
+
+[[tool.mypy.overrides]]
+module = "pylet.errors"
+disallow_untyped_defs = true
+
+# db.py uses Optional[Connection] but methods assume connect() was called
+[[tool.mypy.overrides]]
+module = "pylet.db"
+disable_error_code = ["union-attr"]