Add logging to track process creation paths on Windows

Added comprehensive logging to help debug CI/local differences:
- Log which platform path is taken (Windows vs Unix/Linux)
- Log which Windows process type is created (anyio vs FallbackProcess)
- Log any errors that cause fallbacks to different process creation methods
- Include command names in logs for easier debugging

This will help determine if CI and local environments are using different
process creation mechanisms, which could explain test behavior differences.

Author: felixweinberger

src/mcp/client/stdio/__init__.py

@@ -1,3 +1,4 @@
+import logging
 import os
 import sys
 from contextlib import asynccontextmanager
@@ -18,6 +19,8 @@
     get_windows_executable_command,
 )
 
+logger = logging.getLogger(__name__)
+
 # Environment variables to inherit by default
 DEFAULT_INHERITED_ENV_VARS = (
     [
@@ -240,8 +243,10 @@ async def _create_platform_compatible_process(
     Returns a process handle.
     """
     if sys.platform == "win32":
+        logger.info(f"Creating Windows process for command: {command}")
         process = await create_windows_process(command, args, env, errlog, cwd)
     else:
+        logger.info(f"Creating Unix/Linux process using anyio for command: {command}")
         process = await anyio.open_process([command, *args], env=env, stderr=errlog, cwd=cwd)
 
     return process

src/mcp/client/stdio/win32.py

@@ -2,6 +2,7 @@
 Windows-specific functionality for stdio client operations.
 """
 
+import logging
 import shutil
 import subprocess
 import sys
@@ -13,6 +14,8 @@
 from anyio.abc import Process
 from anyio.streams.file import FileReadStream, FileWriteStream
 
+logger = logging.getLogger(__name__)
+
 
 def get_windows_executable_command(command: str) -> str:
     """
@@ -144,17 +147,27 @@ async def create_windows_process(
             if hasattr(subprocess, "CREATE_NO_WINDOW")
             else 0,
         )
+        logger.info(f"Created Windows process using anyio.open_process for command: {command}")
         return process
-    except NotImplementedError:
+    except NotImplementedError as e:
+        logger.info(
+            f"anyio.open_process not available (NotImplementedError), "
+            f"falling back to FallbackProcess for command: {command}. Error: {e}"
+        )
         return _create_windows_fallback_process(command, args, env, errlog, cwd)
-    except Exception:
+    except Exception as e:
         # If anyio failed for other reasons, try without creation flags
+        logger.info(
+            f"anyio.open_process failed with creation flags, "
+            f"retrying without flags for command: {command}. Error: {e}"
+        )
         process = await anyio.open_process(
             [command, *args],
             env=env,
             stderr=errlog,
             cwd=cwd,
         )
+        logger.info(f"Created Windows process using anyio.open_process (without flags) for command: {command}")
         return process
 
 
@@ -192,9 +205,13 @@ def _create_windows_fallback_process(
             bufsize=0,  # Unbuffered output
             creationflags=getattr(subprocess, "CREATE_NO_WINDOW", 0),
         )
+        logger.info(f"Created FallbackProcess with creation flags for command: {command}")
         return FallbackProcess(popen_obj)
-    except Exception:
+    except Exception as e:
         # If creationflags failed, try without them
+        logger.info(
+            f"FallbackProcess with creation flags failed, " f"retrying without flags for command: {command}. Error: {e}"
+        )
         popen_obj = subprocess.Popen(
             [command, *args],
             stdin=subprocess.PIPE,
@@ -204,4 +221,5 @@ def _create_windows_fallback_process(
             cwd=cwd,
             bufsize=0,
         )
+        logger.info(f"Created FallbackProcess without creation flags for command: {command}")
         return FallbackProcess(popen_obj)