fix(windows): terminal drain and cwd path conversion for native Windows

Two fixes for the local terminal backend on Windows (Git Bash):

1. `_drain()` in base.py: `select.select()` only works on sockets on
   Windows, not pipe file descriptors. On Windows, use blocking
   `os.read()` in the daemon thread instead. EOF arrives promptly
   when bash exits, so this is safe.

2. `_run_bash()` in local.py: When `self.cwd` is updated from `pwd`
   output, it contains Git Bash-style paths (`/c/Users/...`).
   `subprocess.Popen(cwd=...)` needs a native Windows path
   (`C:\Users\...`). Added a conversion before Popen.

Without these fixes, all terminal() calls on Windows return empty
output (exit code 126), and cwd tracking breaks.

Tested on Windows 11 with Git for Windows + Python 3.13.

Fixes #14638

tools/environments/local.py

@@ -3,6 +3,7 @@
 import logging
 import os
 import platform
+import re
 import shutil
 import signal
 import subprocess
@@ -403,6 +404,12 @@ class LocalEnvironment(BaseEnvironment):
             )
             self.cwd = safe_cwd
 
+        # On Windows, self.cwd may be a Git Bash-style path (/c/Users/...)
+        # from pwd output. subprocess.Popen needs a native Windows path.
+        _popen_cwd = self.cwd
+        if _IS_WINDOWS and _popen_cwd and re.match(r'^/[a-zA-Z]/', _popen_cwd):
+            _popen_cwd = _popen_cwd[1].upper() + ':' + _popen_cwd[2:].replace('/', '\\')
+
         proc = subprocess.Popen(
             args,
             text=True,
@@ -413,7 +420,7 @@ class LocalEnvironment(BaseEnvironment):
             stderr=subprocess.STDOUT,
             stdin=subprocess.PIPE if stdin_data is not None else subprocess.DEVNULL,
             preexec_fn=None if _IS_WINDOWS else os.setsid,
-            cwd=self.cwd,
+            cwd=_popen_cwd,
         )
         if not _IS_WINDOWS:
             try: