fix(tools): stop the Git Bash probe from inheriting host stdin

tests/tools/test_find_shell.py

@@ -145,6 +145,32 @@ def fake_run(argv, **kwargs):
         assert local_mod._bash_starts(r"C:\Git\bin\bash.exe") is True
         assert calls[0][0][-1] == "/usr/bin/true; /usr/bin/cat --version >/dev/null"
 
+    def test_probe_never_inherits_host_stdin(self, monkeypatch):
+        """The probe must not inherit fd 0 (#73693).
+
+        Under a JSON-RPC stdio host — ACP, or the TUI gateway of #14036 —
+        stdin is the protocol pipe. MSYS bash blocks on it at startup, and
+        the probe's own timeout only reaps the Git wrapper process, so the
+        surviving mingw child holds the pipe and hangs the turn.
+        """
+        import tools.environments.local as local_mod
+
+        local_mod._bash_starts_cache.clear()
+        local_mod._bash_probe_details_cache.clear()
+        calls = []
+
+        def fake_run(argv, **kwargs):
+            calls.append(kwargs)
+            return subprocess.CompletedProcess(argv, 0, stdout="", stderr="")
+
+        monkeypatch.setattr(local_mod.subprocess, "run", fake_run)
+        monkeypatch.setattr(local_mod, "_IS_WINDOWS", True)
+
+        local_mod._bash_starts(r"C:\Git\bin\bash.exe")
+
+        assert calls, "expected the probe to spawn bash"
+        assert calls[0].get("stdin") is subprocess.DEVNULL
+
     def test_aslr_failure_surfaces_targeted_windows_command(
         self, tmp_path, monkeypatch
     ):

tools/environments/local.py

@@ -845,6 +845,7 @@ def _mandatory_aslr_enabled() -> "bool | None":
                 "(Get-ProcessMitigation -System).Aslr.ForceRelocateImages.ToString()",
             ],
             capture_output=True,
+            stdin=subprocess.DEVNULL,
             text=True, encoding="utf-8", errors="replace",
             timeout=10,
             creationflags=windows_hide_flags(),
@@ -911,6 +912,12 @@ def _bash_starts(bash: str) -> bool:
         result = subprocess.run(
             [bash, "--noprofile", "--norc", "-c", _BASH_EXTERNAL_PROGRAM_PROBE],
             capture_output=True,
+            # Never let the probe inherit the host's stdin. Under a JSON-RPC
+            # stdio host (ACP/TUI gateway) fd 0 is the protocol pipe; MSYS
+            # bash blocks on it at startup, and the timeout below then kills
+            # only the Git\bin wrapper — the surviving mingw child keeps the
+            # pipe open and communicate() hangs the turn. See #73693.
+            stdin=subprocess.DEVNULL,
             text=True, encoding="utf-8", errors="replace",
             timeout=15,
             creationflags=windows_hide_flags() if _IS_WINDOWS else 0,