Merge PR #7696: fix(coding-agent): stop Python eval shell children inheriting the runner control channel; resolve Git Bash on Windows (@metaphorics)

packages/coding-agent/src/eval/py/runner.py

@@ -40,6 +40,7 @@ import os
 import re
 import runpy
 import shlex
+import shutil
 import signal
 import subprocess
 import sys
@@ -576,8 +577,10 @@ class _BoundedLineScanner:
 def _magic_pip(args: str) -> None:
     argv = shlex.split(args) if args else ["--help"]
     cmd = [sys.executable, "-m", "pip", *argv]
+    # stdin=DEVNULL: see _run_shell_body.
     proc = subprocess.Popen(
         cmd,
+        stdin=subprocess.DEVNULL,
         stdout=subprocess.PIPE,
         stderr=subprocess.STDOUT,
     )
@@ -737,9 +740,37 @@ def _magic_run(args: str) -> None:
         _STATE.user_ns[name] = value
 
 
+def _resolve_bash() -> str:
+    if os.name != "nt":
+        return "/bin/bash"
+    # Prefer Git Bash over WSL's System32 bash.exe, which runs inside a
+    # separate Linux environment and does not share the Windows filesystem
+    # layout or PATH.
+    for env_var, suffix in (
+        ("ProgramFiles", r"Git\bin\bash.exe"),
+        ("ProgramFiles(x86)", r"Git\bin\bash.exe"),
+        ("LOCALAPPDATA", r"Programs\Git\bin\bash.exe"),
+    ):
+        root = os.environ.get(env_var)
+        if root:
+            candidate = os.path.join(root, suffix)
+            if os.path.isfile(candidate):
+                return candidate
+    found = shutil.which("bash")
+    if found and "system32" not in found.lower():
+        return found
+    # WSL's System32 bash.exe runs in a separate Linux environment, so
+    # silently falling back to it would execute the cell somewhere the user
+    # did not intend; fail loudly instead.
+    raise RuntimeError(
+        "%%bash requires a POSIX bash, but none was found. "
+        "Install Git for Windows or add a non-WSL bash to PATH."
+    )
+
+
 @cell_magic("bash")
 def _magic_cell_bash(args: str, body: str) -> int:
-    return _run_shell_body(body, shell_arg="/bin/bash")
+    return _run_shell_body(body, shell_arg=_resolve_bash())
 
 
 @cell_magic("capture")
@@ -780,8 +811,12 @@ def _magic_cell_writefile(args: str, body: str) -> str:
 
 
 def _run_shell_body(body: str, *, shell_arg: str) -> int:
+    # stdin=DEVNULL: children must not inherit the runner's stdin, which is
+    # the host's NDJSON control channel (a reading child would steal frames,
+    # and inheriting the pipe deadlocks nested interpreters on Windows).
     proc = subprocess.Popen(
         [shell_arg, "-c", body],
+        stdin=subprocess.DEVNULL,
         stdout=subprocess.PIPE,
         stderr=subprocess.STDOUT,
     )
@@ -821,9 +856,11 @@ class _ShellResult(list):
 
 
 def __omp_shell(cmd: str) -> _ShellResult:
+    # stdin=DEVNULL: see _run_shell_body.
     proc = subprocess.Popen(
         cmd,
         shell=True,
+        stdin=subprocess.DEVNULL,
         stdout=subprocess.PIPE,
         stderr=subprocess.STDOUT,
     )