FEATURE-ci-windows-stage-fixture: use the selected MSYS shell for real staging tests

Convert configure and executable handoffs through cygpath while retaining the native DOS prefix and all eight original staging assertions. Real Linux fixtures and the executed Windows-branch boundary pass; native Windows confirmation and full caller validation remain pending.

Author: etr

scripts/test-v3-stage-install.py

@@ -2,6 +2,7 @@
 """Exercise configured staging recipes and real Automake/libtool installation."""
 import os
 from pathlib import Path
+import platform
 import shlex
 import shutil
 import subprocess
@@ -23,6 +24,13 @@ def setUpClass(cls):
         cls.build = Path(cls.temporary.name).resolve()
         cls.environment = {key: value for key, value in os.environ.items()
                            if key not in ('MAKEFLAGS', 'MFLAGS', 'MAKELEVEL')}
+        cls.shell = 'sh'
+        if platform.system() == 'Windows':
+            # Bypass Windows system-shell lookup and use the selected MSYS tools.
+            shell = shutil.which('bash', path=cls.environment.get('PATH', ''))
+            if not shell:
+                raise RuntimeError('bash is unavailable on the selected PATH')
+            cls.shell = str(Path(shell).resolve())
         for tool in ('install', 'ranlib'):
             boundary = cls.build / f'native-{tool}-boundary.sh'
             boundary.write_text(
@@ -33,12 +41,12 @@ def setUpClass(cls):
                 f'  /*[a-zA-Z]:/*) echo "native {tool} rejects embedded drive: $destination" >&2; exit 1 ;;\n'
                 'esac\n'
                 f'printf "%s\\n" "$destination" >> {tool}-destinations.log\n'
-                f'exec {shlex.quote(Path(shutil.which(tool)).as_posix())} "$@"\n')
+                f'exec {shlex.quote(cls.shell_path(Path(shutil.which(tool))))} "$@"\n')
             boundary.chmod(0o755)
         result = subprocess.run(
-            ['sh', (SOURCE / 'configure').as_posix(), '--disable-v3-tls',
+            [cls.shell, cls.shell_path(SOURCE / 'configure'), '--disable-v3-tls',
              '--disable-examples', '--prefix=D:/ci/prefix',
-             'RANLIB=' + (cls.build / 'native-ranlib-boundary.sh').as_posix()], cwd=cls.build,
+             'RANLIB=' + cls.shell_path(cls.build / 'native-ranlib-boundary.sh')], cwd=cls.build,
             env=cls.environment, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True)
         if result.returncode:
             raise RuntimeError(result.stdout)
@@ -53,12 +61,21 @@ def setUpClass(cls):
                 ['--mode=compile'] + compiler + ['-c', 'stagefixture.cpp', '-o', 'stagefixture.lo'],
                 ['--mode=link'] + compiler + ['-o', 'libstagefixture.la', 'stagefixture.lo',
                  '-rpath', '/stagefixture', '-no-undefined']]:
-            result = subprocess.run(['sh', '../libtool', '--tag=CXX'] + arguments,
+            result = subprocess.run([cls.shell, '../libtool', '--tag=CXX'] + arguments,
                                     cwd=cls.build / 'src', env=cls.environment, stdout=subprocess.PIPE,
                                     stderr=subprocess.STDOUT, text=True)
             if result.returncode:
                 raise RuntimeError(result.stdout)
 
+    @classmethod
+    def shell_path(cls, path):
+        if platform.system() != 'Windows':
+            return path.as_posix()
+        # Autoconf's ':'-separated source search requires MSYS drive notation.
+        return subprocess.check_output(
+            [cls.shell, '-c', 'cygpath -u "$1"', 'stage-path', path.as_posix()],
+            cwd=cls.build, env=cls.environment, text=True).strip()
+
     def setUp(self):
         for name in ('.hygiene-stage', '.install-stage', '.shared-check-stage', 'missing-stage'):
             shutil.rmtree(self.build / name, ignore_errors=True)
@@ -70,7 +87,7 @@ def make(self, target, *variables, shared=False):
         # Only the fixture archive replaces the unrelated protocol engines.
         command = [MAKE, '--no-print-directory', target,
                    'lib_LTLIBRARIES=libstagefixture.la', 'noinst_LTLIBRARIES=', 'noinst_PROGRAMS=',
-                   'INSTALL=' + self.installer.as_posix()]
+                   'INSTALL=' + self.shell_path(self.installer)]
         if shared:
             # Only check-local's staged-install body is under test here.
             text = (SOURCE / 'Makefile.am').read_text()

specs/tasks/FEATURE-ci-windows-stage-fixture.md

@@ -0,0 +1,57 @@
+# FEATURE-ci-windows-stage-fixture: execute the real staging fixture through MSYS
+
+Status: In Progress — implementation committed; caller validation/finalization pending.
+Base: local `v3` at `337f6161be9897e590fa5155658582f3dca7cd34`.
+
+Native Windows job `120582231736` fails the new staged-install fixture during
+configure setup, before any tests run. Bootstrap installed the auxiliary files;
+the fixture handed an unqualified shell a native drive-bearing source path.
+Autoconf splits auxiliary-file search directories on `:`, so configure needs an
+MSYS source path. The configured `D:/ci/prefix` remains the staging test subject.
+
+Action items:
+
+- [x] Read primary checkout CLAUDE.md/AGENTS.md, saved plan, literal journal,
+  retained native failure log, complete fixture and existing production adapter.
+- [x] Create the Groundwork task worktree from exact local v3, preserving other work.
+- [x] Use the absolute PATH-selected bash on Windows for configure, path conversion
+  and both real libtool invocations; fail if the selected PATH has no bash.
+- [x] Convert source-script and installer/ranlib executable handoffs with actual
+  `cygpath -u` in the selected shell. Keep `--prefix=D:/ci/prefix` unchanged.
+- [x] Preserve all eight real configured Makefile/libtool/installed-header cases
+  and all original negative assertions without skips or mock configure.
+- [x] Run the real eight-case local regression and source-bound executed boundary
+  proof; check syntax, unchanged test bodies/production sources and diff whitespace.
+- [ ] Caller: full required Groundwork validation and finalization into v3.
+- [ ] Caller: composed conventions review of `c0cfdabc..final-task-HEAD` against
+  primary checkout CLAUDE.md; carry other cleared profiles unless disturbed.
+- [ ] CI / v3 PR: fresh native Windows checkout/archive installed matrices.
+
+Local evidence:
+
+- Native RED: retained raw job log shows `cannot find required auxiliary files:
+  compile ltmain.sh config.guess config.sub missing install-sh`, `Ran 0 tests`.
+- `./bootstrap` passes with existing .PHONY / AC_OUTPUT warnings.
+- `python3 scripts/test-v3-stage-install.py -v`: all 8 tests pass in 19.040s.
+- A bounded Linux counterfactual invokes actual configure through bash with a
+  colon-bearing source alias and reproduces the auxiliary-file error. A controlled
+  conversion-output boundary then executes the fixture's Windows branch, real
+  configure, libtool compile/link, recursive installs and installed production
+  header checks: all 8 cases pass in 18.199s. Recorded argv uses absolute
+  `/usr/bin/bash`, the converted source alias and unchanged `--prefix=D:/ci/prefix`.
+  Linux has no MSYS cygpath; only its output is controlled in this probe. This
+  proves local argument handoff and real fixture behavior, not native Windows.
+- Python AST syntax, all eight original test-method ASTs and `git diff --check`
+  pass. Production Makefile.am, src/Makefile.am and installed-consumer driver are
+  byte-for-byte unchanged. CLAUDE.md documents C++ cpplint, which does not apply
+  to this Python-only change; no Python lint command is documented.
+
+The initial local boundary probe used a POSIX source alias containing spaces;
+configure rejected its unsafe srcdir. The corrected probe uses hyphenated source
+aliases and retains the failed setup log. No product change addressed that probe
+setup. Exact commands, source SHA-256 bindings, argv receipts, tool versions and
+limits are in the primary checkout's literal journal
+`.debug/ci-windows-stage-fixture-qf96yslm/journal.md` and `implementation/`.
+No full baseline, runtime/provider/dependency change, old platform diagnostic,
+CI retry/cancellation, validation loop, merge or publication ran. Native Windows
+checks remain incomplete and CI/v3-PR owned under AGENTS.md.