fix(skills): resolve git through PATH in the retrospective's git script, and write its fake git in Python (#2927)

On Windows a bare "git" handed to CreateProcess finds only git.exe, so a
git.cmd or git.bat ahead of it on PATH was never run. The script now resolves
git with shutil.which, which honours PATHEXT.

The tests' fake git was an sh script, which Windows cannot run, so four tests
failed there. It is now a Python script behind a launcher: git.cmd on Windows,
an sh one-liner elsewhere.

skills/bmad-retrospective/scripts/git_evidence.py

@@ -20,6 +20,7 @@ import argparse
 import json
 import os
 import re
+import shutil
 import subprocess
 import sys
 
@@ -75,7 +76,9 @@ def _git_log(repo, extra_args, rng):
     `merges_measured` and read as "the merges changed nothing".
     """
     cmd = [
-        "git",
+        # Resolved here, not left to the OS: on Windows a bare "git" finds only
+        # git.exe, never a git.cmd or git.bat ahead of it on PATH.
+        shutil.which("git") or "git",
         "-c",
         "core.quotePath=false",
         "-c",

skills/bmad-retrospective/scripts/tests/test_git_evidence.py

@@ -273,12 +273,20 @@ def _rev(repo, ref):
 def _fake_git(tmp_path, body):
     """Write a `git` shim and return the PATH overlay that puts it ahead of the
     real binary for the script's own subprocesses (never for the fixtures,
-    which build their repos through `_git`'s own environment)."""
+    which build their repos through `_git`'s own environment).
+
+    `body` is Python, run by the tests' own interpreter, so one shim serves
+    every platform. Only its launcher differs: Windows runs a `git.cmd`."""
     bindir = tmp_path / "fakebin"
     bindir.mkdir()
-    shim = bindir / "git"
-    shim.write_text(body)
-    os.chmod(shim, 0o755)
+    script = bindir / "fake_git.py"
+    script.write_text(body)
+    if os.name == "nt":
+        (bindir / "git.cmd").write_text(f'@"{sys.executable}" "{script}" %*\n')
+    else:
+        shim = bindir / "git"
+        shim.write_text(f'#!/bin/sh\nexec "{sys.executable}" "{script}" "$@"\n')
+        os.chmod(shim, 0o755)
     return {"PATH": f"{bindir}{os.pathsep}{os.environ['PATH']}"}
 
 
@@ -475,7 +483,8 @@ def test_distinct_non_utf8_paths_stay_distinct(tmp_path):
     # measurement corruption with nothing in the output admitting to it.
     overlay = _fake_git(
         tmp_path,
-        "#!/bin/sh\nprintf 'aaaa\\037\\037subj\\n\\n1\\t0\\tsrc/caf\\351.py\\n2\\t0\\tsrc/caf\\377.py\\n'\n",
+        "import sys\n"
+        "sys.stdout.buffer.write(b'aaaa\\x1f\\x1fsubj\\n\\n1\\t0\\tsrc/caf\\xe9.py\\n2\\t0\\tsrc/caf\\xff.py\\n')\n",
     )
     out = _json(_proc("--repo", str(tmp_path), "--range", "a..b", env=overlay))
     files = {f["path"]: f for f in out["files"]}
@@ -495,15 +504,12 @@ def test_repeated_merge_headers_are_counted_once(tmp_path):
     repo, base = _merge_repo(tmp_path)
     overlay = _fake_git(
         tmp_path,
-        "#!/bin/sh\n"
-        'for a in "$@"; do\n'
-        '  if [ "$a" = "--min-parents=2" ]; then\n'
-        "    printf 'aaaa\\037p1 p2\\037merge story 1-3\\n\\n2\\t1\\ts.py\\n"
-        "aaaa\\037p1 p2\\037merge story 1-3\\n\\n5\\t4\\ts.py\\n'\n"
-        "    exit 0\n"
-        "  fi\n"
-        "done\n"
-        f'exec "{real_git}" "$@"\n',
+        "import subprocess, sys\n"
+        "if '--min-parents=2' in sys.argv:\n"
+        "    sys.stdout.buffer.write(b'aaaa\\x1fp1 p2\\x1fmerge story 1-3\\n\\n2\\t1\\ts.py\\n'\n"
+        "                            b'aaaa\\x1fp1 p2\\x1fmerge story 1-3\\n\\n5\\t4\\ts.py\\n')\n"
+        "    sys.exit(0)\n"
+        f"sys.exit(subprocess.run([{real_git!r}, *sys.argv[1:]]).returncode)\n",
     )
     out = _json(_proc("--repo", str(repo), "--range", f"{base}..HEAD", env=overlay))
     # One merge sha, however many blocks git printed for it.
@@ -556,7 +562,10 @@ def _recording_git(tmp_path, calls):
     assert real_git, "git must be on PATH"
     return _fake_git(
         tmp_path,
-        f'#!/bin/sh\n( printf \'%s\\037\' "$@"; printf \'\\n\' ) >> "{calls}"\nexec "{real_git}" "$@"\n',
+        "import subprocess, sys\n"
+        f"with open({str(calls)!r}, 'a') as log:\n"
+        "    log.write(''.join(a + '\\x1f' for a in sys.argv[1:]) + '\\n')\n"
+        f"sys.exit(subprocess.run([{real_git!r}, *sys.argv[1:]]).returncode)\n",
     )
 
 
@@ -636,7 +645,7 @@ def test_subject_naming_no_story_gets_an_empty_list(tmp_path):
 def test_git_failure_with_empty_stderr_reports_the_exit_code(tmp_path):
     # A quiet git failure (signal kill, empty stderr) must not leave the caller
     # with `"error": ""` and nothing to report.
-    overlay = _fake_git(tmp_path, "#!/bin/sh\nexit 3\n")
+    overlay = _fake_git(tmp_path, "import sys\nsys.exit(3)\n")
     proc = _proc("--repo", str(tmp_path), "--range", "HEAD~1..HEAD", env=overlay)
     out = _json(proc)
     assert proc.returncode == 1