fix(file-tools): normalize MSYS paths to prevent Windows ghost tree writes

tests/tools/test_windows_native_support.py

@@ -1007,3 +1007,88 @@ def test_launch_detached_profile_gateway_restart_outer_popen_has_access_denied_f
             "CreateProcess and retry without the breakaway bit, matching "
             "gateway_windows._spawn_detached's fallback pattern."
         )
+
+
+# ---------------------------------------------------------------------------
+# file_tools MSYS path normalisation (issue #46876)
+# ---------------------------------------------------------------------------
+
+
+class TestFileToolsMsysPathNormalization:
+    """_normalize_msys_path in file_tools must translate /c/Users/... to
+    C:\\Users\\... on Windows, preventing writes to the ghost tree
+    C:\\c\\Users\\... that pathlib.Path.resolve() produces when given a
+    drive-less POSIX path on Windows (issue #46876)."""
+
+    def test_posix_host_noop(self):
+        """On non-Windows the function must be a no-op for MSYS-style paths."""
+        if sys.platform == "win32":
+            pytest.skip("POSIX no-op test only valid on non-Windows")
+        from tools.file_tools import _normalize_msys_path
+        assert _normalize_msys_path("/c/Users/foo") == "/c/Users/foo"
+        assert _normalize_msys_path("/home/user/project") == "/home/user/project"
+        assert _normalize_msys_path("relative/path") == "relative/path"
+
+    def test_empty_string(self):
+        from tools.file_tools import _normalize_msys_path
+        assert _normalize_msys_path("") == ""
+
+    def test_windows_drive_c(self, monkeypatch):
+        """Simulate Windows: /c/Users/foo → C:\\Users\\foo."""
+        import tools.file_tools as ft
+        monkeypatch.setattr(ft, "_IS_WINDOWS", True)
+        assert ft._normalize_msys_path("/c/Users/MarkChristian/project") == r"C:\Users\MarkChristian\project"
+        assert ft._normalize_msys_path("/C/Users/MarkChristian/project") == r"C:\Users\MarkChristian\project"
+
+    def test_windows_drive_d(self, monkeypatch):
+        import tools.file_tools as ft
+        monkeypatch.setattr(ft, "_IS_WINDOWS", True)
+        assert ft._normalize_msys_path("/d/workspace/repo") == r"D:\workspace\repo"
+
+    def test_windows_bare_drive_root(self, monkeypatch):
+        """Bare drive root /c → C:\\."""
+        import tools.file_tools as ft
+        monkeypatch.setattr(ft, "_IS_WINDOWS", True)
+        assert ft._normalize_msys_path("/c") == "C:\\"
+
+    def test_windows_native_path_unchanged(self, monkeypatch):
+        """Already-native Windows path must pass through unchanged."""
+        import tools.file_tools as ft
+        monkeypatch.setattr(ft, "_IS_WINDOWS", True)
+        assert ft._normalize_msys_path(r"C:\Users\foo") == r"C:\Users\foo"
+        assert ft._normalize_msys_path("C:/Users/foo") == "C:/Users/foo"
+
+    def test_windows_non_drive_absolute_unchanged(self, monkeypatch):
+        """/etc/hosts is not an MSYS drive path — must not be translated."""
+        import tools.file_tools as ft
+        monkeypatch.setattr(ft, "_IS_WINDOWS", True)
+        assert ft._normalize_msys_path("/etc/hosts") == "/etc/hosts"
+
+    def test_normalize_called_in_sentinel_free_abs_cwd(self):
+        """Source check: _sentinel_free_abs_cwd must call _normalize_msys_path
+        so TERMINAL_CWD from config.yaml is translated on Windows."""
+        root = Path(__file__).resolve().parents[2]
+        source = (root / "tools" / "file_tools.py").read_text(encoding="utf-8")
+        # The call must appear inside _sentinel_free_abs_cwd
+        fn_start = source.find("def _sentinel_free_abs_cwd(")
+        fn_end = source.find("\ndef ", fn_start + 1)
+        fn_body = source[fn_start:fn_end]
+        assert "_normalize_msys_path" in fn_body, (
+            "_sentinel_free_abs_cwd must call _normalize_msys_path so "
+            "TERMINAL_CWD=/c/Users/... from config.yaml is translated to "
+            "C:\\Users\\... on Windows before the isabs check (issue #46876)."
+        )
+
+    def test_normalize_called_in_resolve_path_for_task(self):
+        """Source check: _resolve_path_for_task must call _normalize_msys_path
+        so agent-supplied /c/Users/... paths don't become ghost C:\\c\\Users\\..."""
+        root = Path(__file__).resolve().parents[2]
+        source = (root / "tools" / "file_tools.py").read_text(encoding="utf-8")
+        fn_start = source.find("def _resolve_path_for_task(")
+        fn_end = source.find("\ndef ", fn_start + 1)
+        fn_body = source[fn_start:fn_end]
+        assert "_normalize_msys_path" in fn_body, (
+            "_resolve_path_for_task must call _normalize_msys_path so "
+            "write_file/patch don't silently route to the C:\\c\\... ghost "
+            "tree when the agent uses Git Bash paths (issue #46876)."
+        )

tools/file_tools.py

@@ -5,6 +5,8 @@
 import json
 import logging
 import os
+import platform
+import re
 import threading
 from pathlib import Path
 
@@ -20,6 +22,27 @@
 
 logger = logging.getLogger(__name__)
 
+_IS_WINDOWS = platform.system() == "Windows"
+
+
+def _normalize_msys_path(filepath: str) -> str:
+    """Translate a Git Bash / MSYS-style POSIX path (``/c/Users/x``) to the
+    native Windows form (``C:\\Users\\x``).
+
+    No-op on non-Windows hosts or paths that are not in MSYS drive-letter form.
+    Idempotent — already-native Windows paths pass through unchanged.
+    Mirrors ``tools.environments.local._msys_to_windows_path`` so file tools
+    apply the same translation as the terminal backend (fixes #46876).
+    """
+    if not _IS_WINDOWS or not filepath:
+        return filepath
+    m = re.match(r'^/([a-zA-Z])(/.*)?$', filepath)
+    if not m:
+        return filepath
+    drive = m.group(1).upper()
+    tail = (m.group(2) or "").replace('/', '\\')
+    return f"{drive}:{tail or chr(92)}"  # chr(92) == backslash
+
 
 _EXPECTED_WRITE_ERRNOS = {errno.EACCES, errno.EPERM, errno.EROFS}
 
@@ -107,7 +130,7 @@ def _sentinel_free_abs_cwd(raw: str | None) -> str | None:
     raw = str(raw or "").strip()
     if raw.lower() in _TERMINAL_CWD_SENTINELS:
         return None
-    expanded = os.path.expanduser(raw)
+    expanded = os.path.expanduser(_normalize_msys_path(raw))
     if not os.path.isabs(expanded):
         return None
     return expanded
@@ -239,7 +262,7 @@ def _resolve_path_for_task(filepath: str, task_id: str = "default") -> Path:
     See :func:`_resolve_base_dir` for how the base is chosen. Absolute input
     paths are returned resolved-but-unanchored.
     """
-    p = Path(filepath).expanduser()
+    p = Path(_normalize_msys_path(filepath)).expanduser()
     if p.is_absolute():
         return p.resolve()
     return (_resolve_base_dir(task_id) / p).resolve()