fix(mypy): resolve boto3 S3 typing issues in files.py

Add boto3-stubs[s3] dev dependency and use TYPE_CHECKING with cast() to
provide proper S3Client type hints while avoiding boto3-stubs' overly
strict overload definitions.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

pyproject.toml

@@ -67,8 +67,8 @@ dev = [
     "pytest-cov",
     "pytest-html",
     "pytest-json-report",
-    "pytest-socket",       # For blocking network access in unit tests
-    "nbval",               # For notebook testing
+    "pytest-socket", # For blocking network access in unit tests
+    "nbval", # For notebook testing
     "black",
     "ruff",
     "mypy",
@@ -78,9 +78,9 @@ dev = [
     "pandas-stubs",
     "types-psutil",
     "types-tqdm",
-    "boto3-stubs",
+    "boto3-stubs[s3]",
     "pre-commit",
-    "ruamel.yaml",         # needed for openapi generator
+    "ruamel.yaml", # needed for openapi generator
 ]
 # These are the dependencies required for running unit tests.
 unit = [

src/llama_stack/providers/remote/files/s3/files.py

@@ -6,12 +6,15 @@
 
 import uuid
 from datetime import UTC, datetime
-from typing import Annotated, Any
+from typing import TYPE_CHECKING, Annotated, Any, cast
 
 import boto3
 from botocore.exceptions import BotoCoreError, ClientError, NoCredentialsError
 from fastapi import Depends, File, Form, Response, UploadFile
 
+if TYPE_CHECKING:
+    from mypy_boto3_s3.client import S3Client
+
 from llama_stack.apis.common.errors import ResourceNotFoundError
 from llama_stack.apis.common.responses import Order
 from llama_stack.apis.files import (
@@ -34,7 +37,7 @@ from .config import S3FilesImplConfig
 # TODO: provider data for S3 credentials
 
 
-def _create_s3_client(config: S3FilesImplConfig) -> boto3.client:
+def _create_s3_client(config: S3FilesImplConfig) -> S3Client:
     try:
         s3_config = {
             "region_name": config.region,
@@ -52,13 +55,13 @@ def _create_s3_client(config: S3FilesImplConfig) -> boto3.client:
                 }
             )
 
-        return boto3.client("s3", **s3_config)
+        return cast("S3Client", boto3.client("s3", **s3_config))  # type: ignore[call-overload]
 
     except (BotoCoreError, NoCredentialsError) as e:
         raise RuntimeError(f"Failed to initialize S3 client: {e}") from e
 
 
-async def _create_bucket_if_not_exists(client: boto3.client, config: S3FilesImplConfig) -> None:
+async def _create_bucket_if_not_exists(client: S3Client, config: S3FilesImplConfig) -> None:
     try:
         client.head_bucket(Bucket=config.bucket_name)
     except ClientError as e:
@@ -76,7 +79,7 @@ async def _create_bucket_if_not_exists(client: boto3.client, config: S3FilesImpl
                 else:
                     client.create_bucket(
                         Bucket=config.bucket_name,
-                        CreateBucketConfiguration={"LocationConstraint": config.region},
+                        CreateBucketConfiguration=cast(Any, {"LocationConstraint": config.region}),
                     )
             except ClientError as create_error:
                 raise RuntimeError(
@@ -128,7 +131,7 @@ class S3FilesImpl(Files):
     def __init__(self, config: S3FilesImplConfig, policy: list[AccessRule]) -> None:
         self._config = config
         self.policy = policy
-        self._client: boto3.client | None = None
+        self._client: S3Client | None = None
         self._sql_store: AuthorizedSqlStore | None = None
 
     def _now(self) -> int:
@@ -184,7 +187,7 @@ class S3FilesImpl(Files):
         pass
 
     @property
-    def client(self) -> boto3.client:
+    def client(self) -> S3Client:
         assert self._client is not None, "Provider not initialized"
         return self._client
 

uv.lock

@@ -410,6 +410,11 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/83/8a/d14e63701c4e869f1d37ba5657f9821961616b98a30074f20b559c071fb6/boto3_stubs-1.40.60-py3-none-any.whl", hash = "sha256:1ea7f9dbabc7f9ac8477646c12cc51ef49af6b24d53cc2ae8cf6fa6bed6a995a", size = 69746, upload-time = "2025-10-27T19:49:05.619Z" },
 ]
 
+[package.optional-dependencies]
+s3 = [
+    { name = "mypy-boto3-s3" },
+]
+
 [[package]]
 name = "botocore"
 version = "1.40.12"
@@ -1871,7 +1876,7 @@ codegen = [
 ]
 dev = [
     { name = "black" },
-    { name = "boto3-stubs" },
+    { name = "boto3-stubs", extra = ["s3"] },
     { name = "mypy" },
     { name = "nbval" },
     { name = "pandas-stubs" },
@@ -1995,7 +2000,7 @@ codegen = [
 ]
 dev = [
     { name = "black" },
-    { name = "boto3-stubs" },
+    { name = "boto3-stubs", extras = ["s3"] },
     { name = "mypy" },
     { name = "nbval" },
     { name = "pandas-stubs" },
@@ -2568,6 +2573,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/87/e3/be76d87158ebafa0309946c4a73831974d4d6ab4f4ef40c3b53a385a66fd/mypy-1.18.2-py3-none-any.whl", hash = "sha256:22a1748707dd62b58d2ae53562ffc4d7f8bcc727e8ac7cbc69c053ddc874d47e", size = 2352367, upload-time = "2025-09-19T00:10:15.489Z" },
 ]
 
+[[package]]
+name = "mypy-boto3-s3"
+version = "1.40.26"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/00/b8/55d21ed9ca479df66d9892212ba7d7977850ef17aa80a83e3f11f31190fd/mypy_boto3_s3-1.40.26.tar.gz", hash = "sha256:8d2bfd1052894d0e84c9fb9358d838ba0eed0265076c7dd7f45622c770275c99", size = 75948, upload-time = "2025-09-08T20:12:21.405Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/85/a5/dba3384423834009bdd41c7021de5c663468a0e7bc4071cb301721e52a99/mypy_boto3_s3-1.40.26-py3-none-any.whl", hash = "sha256:6d055d16ef89a0133ade92f6b4f09603e4acc31a0f5e8f846edf4eb48f17b5a7", size = 82762, upload-time = "2025-09-08T20:12:19.338Z" },
+]
+
 [[package]]
 name = "mypy-extensions"
 version = "1.1.0"