diff --git a/backend/tests/support/shell.py b/backend/tests/support/shell.py
index 04390d39f1..017774f88f 100644
--- a/backend/tests/support/shell.py
+++ b/backend/tests/support/shell.py
@@ -19,13 +19,26 @@ from pathlib import Path
 import pytest
 
 
+def _git_roots(git: str) -> list[Path]:
+    """Return the two directories the Makefile wrapper probes for the Git root.
+
+    ``scripts/run-with-git-bash.cmd`` checks ``bin\\bash.exe`` under ``git.exe``'s
+    directory and then one level above it. Git for Windows keeps ``git.exe`` in
+    ``<root>/cmd`` (or ``<root>/bin``), so the first entry is the installation
+    root. PortableGit and GitHub Desktop keep it in ``<root>/mingw64/bin``, where
+    only the second entry is; the first is ``<root>/mingw64`` and typically holds
+    no ``bin/bash.exe`` in stock trees. Bash and sh themselves stay at
+    ``<root>/bin`` and ``<root>/usr/bin`` in both layouts.
+    """
+    git_dir = Path(git).resolve().parent
+    return [git_dir.parent, git_dir.parent.parent]
+
+
 def _script_bash_candidates(git: str | None, program_files: str | None, path_bash: str | None) -> list[Path]:
     """Build the ordered bash candidate list for Windows hosts."""
     candidates: list[Path] = []
     if git is not None:
-        # Git for Windows layout: <root>/cmd/git.exe (or <root>/bin/git.exe)
-        # both resolve to <root>/bin/bash.exe two levels up from git's parent.
-        candidates.append(Path(git).resolve().parent.parent / "bin" / "bash.exe")
+        candidates.extend(root / "bin" / "bash.exe" for root in _git_roots(git))
     if program_files:
         candidates.append(Path(program_files) / "Git" / "bin" / "bash.exe")
     if path_bash is not None:
@@ -42,9 +55,9 @@ def _script_sh_candidates(git: str | None, program_files: str | None) -> list[Pa
     """
     candidates: list[Path] = []
     if git is not None:
-        git_root = Path(git).resolve().parent.parent
-        candidates.append(git_root / "bin" / "sh.exe")
-        candidates.append(git_root / "usr" / "bin" / "sh.exe")
+        for root in _git_roots(git):
+            candidates.append(root / "bin" / "sh.exe")
+            candidates.append(root / "usr" / "bin" / "sh.exe")
     if program_files:
         program_files_git = Path(program_files) / "Git"
         candidates.append(program_files_git / "bin" / "sh.exe")
diff --git a/backend/tests/test_support_shell.py b/backend/tests/test_support_shell.py
index d8258475cb..1a0122b9d2 100644
--- a/backend/tests/test_support_shell.py
+++ b/backend/tests/test_support_shell.py
@@ -11,6 +11,8 @@ is exercised on every CI leg.
 from __future__ import annotations
 
 import os
+import shutil
+import subprocess
 from pathlib import Path
 
 import pytest
@@ -100,7 +102,11 @@ def test_git_derived_bash_candidate_comes_first(fake_windows: Path):
     candidates = shell._script_bash_candidates(git=git_exe, program_files=None, path_bash=path_bash)
 
     git_root = (fake_windows / "git" / "cmd" / "git.exe").resolve().parent.parent
-    assert candidates == [git_root / "bin" / "bash.exe", Path(path_bash)]
+    assert candidates == [
+        git_root / "bin" / "bash.exe",
+        git_root.parent / "bin" / "bash.exe",
+        Path(path_bash),
+    ]
 
 
 def test_program_files_bash_used_when_git_absent(fake_windows: Path):
@@ -120,6 +126,8 @@ def test_posix_sh_prefers_git_sh_exe(fake_windows: Path):
     assert candidates == [
         git_root / "bin" / "sh.exe",
         git_root / "usr" / "bin" / "sh.exe",
+        git_root.parent / "bin" / "sh.exe",
+        git_root.parent / "usr" / "bin" / "sh.exe",
     ]
 
 
@@ -134,6 +142,55 @@ def test_posix_sh_falls_back_to_program_files(fake_windows: Path):
     ]
 
 
+def _portablegit_git(fake_windows: Path) -> tuple[Path, str]:
+    """Create a PortableGit layout (``<root>/mingw64/bin/git.exe``) and return it."""
+    git_exe = _touch(fake_windows / "PortableGit" / "mingw64" / "bin" / "git.exe")
+    return (fake_windows / "PortableGit").resolve(), str(git_exe)
+
+
+def test_portablegit_bash_candidate_reaches_the_git_root(fake_windows: Path):
+    git_root, git_exe = _portablegit_git(fake_windows)
+
+    candidates = shell._script_bash_candidates(git=git_exe, program_files=None, path_bash=None)
+
+    assert candidates == [git_root / "mingw64" / "bin" / "bash.exe", git_root / "bin" / "bash.exe"]
+
+
+def test_portablegit_posix_sh_candidate_reaches_the_git_root(fake_windows: Path):
+    git_root, git_exe = _portablegit_git(fake_windows)
+
+    candidates = shell._script_sh_candidates(git=git_exe, program_files=None)
+
+    assert candidates == [
+        git_root / "mingw64" / "bin" / "sh.exe",
+        git_root / "mingw64" / "usr" / "bin" / "sh.exe",
+        git_root / "bin" / "sh.exe",
+        git_root / "usr" / "bin" / "sh.exe",
+    ]
+
+
+@pytest.mark.skipif(os.name != "nt", reason="the Makefile shell wrapper is a cmd.exe script")
+def test_makefile_shell_wrapper_runs_portablegit_bash(tmp_path: Path):
+    """`make` reaches Git Bash when `where git` reports the mingw64 layout.
+
+    A bare ``cmd.exe`` copy stands in for ``bash.exe``: the wrapper only has to
+    locate and launch it, and ``cmd /c echo`` keeps the assertion offline.
+    """
+    git_root = tmp_path / "PortableGit"
+    _touch(git_root / "mingw64" / "bin" / "git.exe")
+    bash = git_root / "bin" / "bash.exe"
+    system_root = Path(os.environ.get("SystemRoot", r"C:\Windows"))
+    bash.parent.mkdir()
+    shutil.copy(system_root / "System32" / "cmd.exe", bash)
+    wrapper = Path(__file__).resolve().parents[2] / "scripts" / "run-with-git-bash.cmd"
+
+    env = {**os.environ, "PATH": os.pathsep.join([str(git_root / "mingw64" / "bin"), str(system_root / "System32")])}
+    result = subprocess.run(["cmd", "/c", str(wrapper), "/c", "echo", "BASH_OK"], capture_output=True, text=True, env=env, timeout=60)
+
+    assert result.returncode == 0, result.stdout + result.stderr
+    assert "BASH_OK" in result.stdout
+
+
 @pytest.mark.skipif(os.name != "nt", reason="real Windows environment reads")
 def test_find_script_bash_never_returns_wsl_or_store_stubs():
     """On a real Windows host the result must not be a stub launcher."""
diff --git a/scripts/AGENTS.md b/scripts/AGENTS.md
index 89aa9a29ca..8b6c329820 100644
--- a/scripts/AGENTS.md
+++ b/scripts/AGENTS.md
@@ -208,6 +208,13 @@ likewise prefix the target with `bash`. This keeps documented `make` commands
 working when a source archive, `core.fileMode=false`, or a non-POSIX filesystem
 does not preserve executable bits.
 
+The Windows wrapper resolves `bash.exe` under the Git installation root, which
+is the parent of `cmd/`, `bin/`, or `mingw64/bin/` depending on the distribution:
+Git for Windows puts `git.exe` in `cmd/`, while PortableGit and GitHub Desktop
+put it in `mingw64/bin/`. Bash and sh stay at `<root>/bin` and `<root>/usr/bin`
+in both layouts. `backend/tests/support/shell.py` mirrors the same rule for the
+shell-script suites.
+
 `make clean` deletes `backend/.deer-flow` (database, users, threads, uploads,
 secrets), which both compose stacks mount into `deer-flow-gateway`. Its recipe
 runs `check-data-not-in-use.sh` before `make stop` (which would stop a live
diff --git a/scripts/run-with-git-bash.cmd b/scripts/run-with-git-bash.cmd
index 8692ca3375..da96b74c84 100644
--- a/scripts/run-with-git-bash.cmd
+++ b/scripts/run-with-git-bash.cmd
@@ -8,9 +8,13 @@ for /f "delims=" %%I in ('where git 2^>NUL') do (
         set "bash_exe=%%~dpI..\bin\bash.exe"
         goto :found_bash
     )
+    if exist "%%~dpI..\..\bin\bash.exe" (
+        set "bash_exe=%%~dpI..\..\bin\bash.exe"
+        goto :found_bash
+    )
 )
 
-echo Could not locate Git for Windows Bash ("..\bin\bash.exe" relative to git on PATH). Ensure Git for Windows is installed and that git and bash.exe are available on PATH.
+echo Could not locate Git for Windows Bash ("bin\bash.exe" under the git root). Ensure Git for Windows is installed and that git and bash.exe are available on PATH.
 exit /b 1
 
 :found_bash