DRAFT: keep automatic Git maintenance out of downstream-gate disposable fixtures (Math-#397 bounded mitigation, R80)

frontiers/downstream_gate_20260925/SOURCE_FILES.json

@@ -45,8 +45,8 @@
       "sha256": "c444e6c347da680aff5bef7f43900e45d52a0cc45081fb7b4def45266d97aac1"
     },
     "test_transition_contract.py": {
-      "bytes": 12679,
-      "sha256": "ab69008b5c0c136dcdf742ecd1213e1c5b4b08e7aa4c9d0747037acaa8633c37"
+      "bytes": 12767,
+      "sha256": "c4bd9631e615bc5ebb393d5e131a7f5c213936577d8c21b6628509645fb327fe"
     }
   },
   "meaning": "Exact identity, not theorem correctness",

frontiers/downstream_gate_20260925/test_transition_contract.py

@@ -137,7 +137,7 @@ def test_git_source_only_change_on_real_commits(self):
             repo = Path(tmp)
             def run(*args):
                 return subprocess.run(['git', '-C', tmp, *args], check=True, capture_output=True).stdout.decode().strip()
-            run('init', '-q'); run('config', 'user.name', 'local test'); run('config', 'user.email', 'test@example.invalid')
+            run('init', '-q'); run('config', 'user.name', 'local test'); run('config', 'user.email', 'test@example.invalid'); run('config', 'maintenance.auto', 'false')
             (repo/'GRAPH.json').write_text(json.dumps(graph())); (repo/'lemma.md').write_text('first statement')
             run('add', '.'); run('commit', '-qm', 'baseline'); old = run('rev-parse', 'HEAD')
             (repo/'lemma.md').write_text('changed statement')
@@ -155,7 +155,7 @@ def _live_fixture(self, tmp, graph_obj):
         repo = Path(tmp)
         def run(*args):
             return subprocess.run(['git', '-C', tmp, *args], check=True, capture_output=True).stdout.decode().strip()
-        run('init', '-q'); run('config', 'user.name', 'local test'); run('config', 'user.email', 'test@example.invalid')
+        run('init', '-q'); run('config', 'user.name', 'local test'); run('config', 'user.email', 'test@example.invalid'); run('config', 'maintenance.auto', 'false')
         (repo/GRAPH_REL).parent.mkdir(parents=True, exist_ok=True)
         (repo/GRAPH_REL).write_text(json.dumps(graph_obj))
         paths = list(D1_COMPONENT_FILES) + ['UNRELATED.md']

tests/test_downstream_gate_git_isolation.py

@@ -0,0 +1,94 @@
+"""Real-Git lifecycle regression for the downstream-gate disposable fixtures.
+
+The actual fixture tests in frontiers/downstream_gate_20260925/test_transition_contract.py
+run in a child interpreter under Trace2. Global and system Git configuration
+are emptied and every inherited GIT_* variable is removed, so the effective
+maintenance.auto value is Git's default unless the fixture sets it
+repository-locally. No maintenance setting is forced at command or environment
+scope: the claim is bounded to that effective configuration and says nothing
+about runners with higher-priority overrides. No fixture, checker or
+subprocess is mocked.
+"""
+import json
+import os
+from pathlib import Path
+import subprocess
+import sys
+import tempfile
+import unittest
+
+
+ROOT = Path(__file__).resolve().parents[1]
+GATE = ROOT / 'frontiers/downstream_gate_20260925'
+FIXTURE_TESTS = (
+    'test_git_source_only_change_on_real_commits',
+    'test_git_d1_component_change_revalidates_d1_d2_d3',
+    'test_git_unrelated_edit_does_not_revalidate_d1',
+    'test_git_pre_repair_graph_misses_component_change',
+)
+
+
+def trace_environment(trace):
+    env = {key: value for key, value in os.environ.items()
+           if not key.startswith('GIT_')}
+    env.update(GIT_CONFIG_NOSYSTEM='1', GIT_CONFIG_GLOBAL=os.devnull,
+               GIT_TRACE2_EVENT=str(trace.resolve()))
+    return env
+
+
+def read_events(trace):
+    return [json.loads(line) for line in trace.read_text().splitlines() if line]
+
+
+def maintenance_commands(events):
+    return [event.get('argv', []) for event in events
+            if event.get('event') == 'child_start'
+            and 'maintenance' in event.get('argv', []) and '--auto' in event.get('argv', [])]
+
+
+def commit_starts(events):
+    return [event for event in events if event.get('event') == 'start'
+            and 'commit' in event.get('argv', [])]
+
+
+class DownstreamGateGitIsolationTests(unittest.TestCase):
+    def test_actual_gate_fixtures_never_launch_automatic_maintenance(self):
+        flags = ['-B', '-O', '-S'] if sys.flags.optimize else ['-B', '-S']
+        names = ['test_transition_contract.TransitionContract.' + name for name in FIXTURE_TESTS]
+        with tempfile.TemporaryDirectory() as td:
+            trace = Path(td) / 'git-trace.jsonl'
+            result = subprocess.run([sys.executable, *flags, '-m', 'unittest', *names],
+                                    cwd=GATE, env=trace_environment(trace),
+                                    capture_output=True, text=True, timeout=120)
+            self.assertEqual(result.returncode, 0, result.stderr)
+            self.assertIn(f'Ran {len(FIXTURE_TESTS)} tests', result.stderr)
+            self.assertNotIn('skipped=', result.stderr)
+            self.assertNotIn('\nERROR:', result.stderr)
+            events = read_events(trace)
+            self.assertGreaterEqual(len(commit_starts(events)), len(FIXTURE_TESTS),
+                                    'trace must observe the real fixture commits')
+            self.assertEqual(maintenance_commands(events), [],
+                             'gate fixture commit launched automatic maintenance before cleanup')
+
+    def test_trace_detects_default_maintenance_in_positive_control(self):
+        with tempfile.TemporaryDirectory() as td:
+            folder = Path(td)
+            root = folder / 'positive-control'
+            root.mkdir()
+            trace = folder / 'positive-trace.jsonl'
+            env = trace_environment(trace)
+            unset = subprocess.run(['git', 'config', '--get', 'maintenance.auto'],
+                                   cwd=folder, env=env, capture_output=True, timeout=30)
+            self.assertEqual(unset.returncode, 1, 'effective maintenance.auto must be Git default here')
+            (root / 'payload').write_bytes(b'synthetic positive control\n')
+            for command in (['git', 'init', '-q'], ['git', 'add', '.'],
+                            ['git', '-c', 'user.name=Gate Fixture',
+                             '-c', 'user.email=fixture@example.invalid',
+                             '-c', 'commit.gpgsign=false', 'commit', '-qm', 'positive control']):
+                subprocess.run(command, cwd=root, env=env, check=True, capture_output=True, timeout=30)
+            self.assertEqual(len(maintenance_commands(read_events(trace))), 1,
+                             'positive control must start automatic maintenance under the default')
+
+
+if __name__ == '__main__':
+    unittest.main()