chore: Use ty for type checking

Makefile

@@ -1,6 +1,6 @@
 SHELL := /bin/bash
 
-.PHONY: help develop install-dev install-deps fixup test test-core test-wheel lint pylint nox
+.PHONY: help develop install-dev install-deps fixup test test-core test-wheel lint pylint typecheck nox
 
 develop: install-dev
 	mise exec -- pre-commit install
@@ -30,6 +30,9 @@ lint:
 pylint:
 	mise exec -- $(MAKE) -C py pylint
 
+typecheck:
+	mise exec -- $(MAKE) -C py typecheck
+
 nox: test
 
 help:
@@ -40,6 +43,7 @@ help:
 	@echo "  install-dev  - Install pinned tools and create/update the repo env via mise"
 	@echo "  lint         - Run pre-commit hooks plus Python SDK pylint via py/Makefile"
 	@echo "  pylint       - Run Python SDK pylint only via py/Makefile"
+	@echo "  typecheck    - Run ty type checker on the Python SDK via py/Makefile"
 	@echo "  nox          - Alias for test"
 	@echo "  test         - Run the Python SDK nox matrix via py/Makefile"
 	@echo "  test-core    - Run Python SDK core tests via py/Makefile"

mise.toml

@@ -12,6 +12,7 @@ _.file = ".env"
 
 [tools]
 ruff = "0.12.7"
+ty = "0.0.23"
 
 [hooks]
 postinstall = "make install-deps"

py/Makefile

@@ -2,7 +2,7 @@ PYTHON ?= python
 UV := $(PYTHON) -m uv
 UV_VERSION := $(shell awk '$$1=="uv" { print $$2 }' ../.tool-versions)
 
-.PHONY: lint pylint test test-wheel _template-version clean fixup build verify-build verify help install-build-deps install-dev install-optional test-core _check-git-clean
+.PHONY: lint pylint typecheck test test-wheel _template-version clean fixup build verify-build verify help install-build-deps install-dev install-optional test-core _check-git-clean
 
 clean:
 	rm -rf build dist
@@ -17,6 +17,9 @@ lint: fixup
 pylint:
 	nox -s pylint
 
+typecheck:
+	ty check
+
 test:
 	nox -x
 
@@ -73,6 +76,7 @@ help:
 	@echo "  install-dev         - Install package in development mode with all dependencies"
 	@echo "  lint                - Run pylint checks"
 	@echo "  pylint              - Run pylint without pre-commit hooks"
+	@echo "  typecheck           - Run ty type checker"
 	@echo "  test                - Run all tests"
 	@echo "  test-core           - Run core tests only"
 	@echo "  test-wheel          - Run tests against built wheel"

py/noxfile.py

@@ -315,6 +315,17 @@ def pylint(session):
     session.run("pylint", "--errors-only", *files)
 
 
+@nox.session(venv_backend="none")
+def typecheck(session):
+    """Run the ty type checker.
+
+    ty is installed via mise (see mise.toml) and reads its configuration from
+    py/ty.toml. It does not need optional vendor packages because
+    allowed-unresolved-imports suppresses those diagnostics.
+    """
+    session.run("ty", "check", *session.posargs, external=True)
+
+
 @nox.session()
 def test_latest_wrappers_novcr(session):
     """Run the latest wrapper tests without vcrpy."""

py/ty.toml

@@ -0,0 +1,65 @@
+[environment]
+python-version = "3.10"
+# Use the repo-level venv for third-party stubs/packages.
+python = "../venv"
+
+[src]
+# Focus on the SDK source tree; integration packages and examples have their
+# own (often uninstalled) dependency surfaces and are better checked separately.
+include = ["src/"]
+exclude = [
+    "**/__pycache__/",
+]
+
+[rules]
+# Start with errors-only to match the existing pylint --errors-only baseline.
+# Warnings can be promoted to errors later as the codebase is cleaned up.
+
+[analysis]
+# Optional provider packages are imported behind try/except guards.
+# Suppress unresolved-import for all of them so ty can run without
+# installing the full dependency surface (matching how test_core works).
+# Use ** to match arbitrarily deep submodules (e.g. opentelemetry.sdk.trace).
+allowed-unresolved-imports = [
+    "agno.**",
+    "agents.**",
+    "anthropic.**",
+    "autoevals.**",
+    "boto3.**",
+    "botocore.**",
+    "braintrust_core.**",
+    "claude_agent_sdk.**",
+    "dspy.**",
+    "google.adk.**",
+    "google.genai.**",
+    "httpx.**",
+    "langchain.**",
+    "langchain_anthropic.**",
+    "langchain_core.**",
+    "langchain_openai.**",
+    "langsmith.**",
+    "litellm.**",
+    "logfire.**",
+    "mcp.**",
+    "openai.**",
+    "opentelemetry.**",
+    "orjson.**",
+    "pydantic_ai.**",
+    "starlette.**",
+    "temporalio.**",
+    "tenacity.**",
+    "uvicorn.**",
+    "aiohttp.**",
+    "anyio.**",
+]
+
+[terminal]
+output-format = "full"
+
+# Relax rules for test files – they use mocks, dynamic fixtures, etc.
+[[overrides]]
+include = ["src/**/test_*.py", "src/**/conftest.py"]
+[overrides.rules]
+invalid-argument-type = "warn"
+unresolved-attribute = "warn"
+call-non-callable = "warn"