test: ensure full candidate probing and clear cache in setUp

- Updates _check_bash_state to not short-circuit on the first unusable
  bash candidate on Windows, ensuring a working fallback is found if present.
- Clears bash detection cache in unittest setUp/tearDown rather than just
  relying on a pytest fixture, covering native unittest runners.

tests/_bash.py

@@ -17,6 +17,7 @@ def _probe_bash(bash_path: str) -> bool:
 
 @functools.lru_cache(maxsize=1)
 def _check_bash_state() -> tuple[str | None, str]:
+    reasons = []
     if os.name == 'nt':
         for candidate in (
             r'C:\Program Files\Git\bin\bash.exe',
@@ -27,12 +28,15 @@ def _check_bash_state() -> tuple[str | None, str]:
             if os.path.exists(candidate):
                 if _probe_bash(candidate):
                     return candidate, ""
-                return None, f"bash present at {candidate} but unusable"
+                reasons.append(f"present at {candidate} but unusable")
     bash = shutil.which('bash')
     if bash and 'WindowsApps' not in bash:
         if _probe_bash(bash):
             return bash, ""
-        return None, f"bash present at {bash} but unusable"
+        reasons.append(f"present at {bash} but unusable")
+    
+    if reasons:
+        return None, "bash found but broken: " + "; ".join(reasons)
     return None, "Requires bash"
 
 def get_bash_executable() -> str | None:

tests/test_pre_push_hook_contract.py

@@ -5,7 +5,7 @@ import subprocess
 import unittest
 from pathlib import Path
 
-from tests._bash import get_bash_executable, require_bash, bash_skip_reason
+from tests._bash import get_bash_executable, require_bash, bash_skip_reason, _check_bash_state
 
 
 REPO_ROOT = Path(__file__).resolve().parents[1]
@@ -13,6 +13,14 @@ PRE_PUSH_HOOK = REPO_ROOT / '.github' / 'hooks' / 'pre-push'
 
 
 class PrePushHookContractTests(unittest.TestCase):
+    def setUp(self) -> None:
+        _check_bash_state.cache_clear()
+        super().setUp()
+
+    def tearDown(self) -> None:
+        _check_bash_state.cache_clear()
+        super().tearDown()
+
     @unittest.skipUnless(require_bash(), bash_skip_reason())
     def test_skip_escape_hatch_exits_successfully_with_stderr_notice(self) -> None:
         bash_cmd = get_bash_executable() or 'bash'

tests/test_roadmap_helpers.py

@@ -14,7 +14,7 @@ REPO_ROOT = Path(__file__).resolve().parents[1]
 NEXT_ID = REPO_ROOT / 'scripts' / 'roadmap-next-id.sh'
 DOGFOOD_PROBE = REPO_ROOT / 'scripts' / 'dogfood-probe.py'
 
-from tests._bash import get_bash_executable, require_bash, bash_skip_reason
+from tests._bash import get_bash_executable, require_bash, bash_skip_reason, _check_bash_state
 
 
 def run_next_id(roadmap: Path, script: Path = NEXT_ID) -> subprocess.CompletedProcess[str]:
@@ -40,6 +40,14 @@ def run_dogfood_probe(args: list[str]) -> subprocess.CompletedProcess[str]:
 
 
 class RoadmapHelperTests(unittest.TestCase):
+    def setUp(self) -> None:
+        _check_bash_state.cache_clear()
+        super().setUp()
+
+    def tearDown(self) -> None:
+        _check_bash_state.cache_clear()
+        super().tearDown()
+
     @unittest.skipUnless(require_bash(), bash_skip_reason())
     def test_roadmap_next_id_prints_only_next_id_after_duplicate_check(self) -> None:
         with tempfile.TemporaryDirectory() as temp_dir: