Prevent pre-push contract drift (#3113)

Add a lightweight regression for the documented local pre-push build gate so the skip hatch and lockfile-grade cargo build command stay aligned with operator docs.

Constraint: Issue #696 scope is limited to pre-push hook contract drift after ROADMAP #694.\nRejected: Reworking the hook harness or roadmap board | unnecessary for the focused drift guard.\nConfidence: high\nScope-risk: narrow\nDirective: Keep the hook docs, skip hatch, and cargo --locked command in sync when changing local push gates.\nTested: bash -n .github/hooks/pre-push; python3 tests/test_pre_push_hook_contract.py -v; git diff --check\nNot-tested: Full cargo workspace build; Rust code was not touched.

tests/test_pre_push_hook_contract.py

@@ -0,0 +1,45 @@
+from __future__ import annotations
+
+import os
+import subprocess
+import unittest
+from pathlib import Path
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+PRE_PUSH_HOOK = REPO_ROOT / '.github' / 'hooks' / 'pre-push'
+
+
+class PrePushHookContractTests(unittest.TestCase):
+    def test_skip_escape_hatch_exits_successfully_with_stderr_notice(self) -> None:
+        env = os.environ.copy()
+        env['SKIP_CLAW_PRE_PUSH_BUILD'] = '1'
+
+        result = subprocess.run(
+            ['bash', str(PRE_PUSH_HOOK)],
+            cwd=REPO_ROOT,
+            env=env,
+            check=True,
+            capture_output=True,
+            text=True,
+        )
+
+        self.assertEqual('', result.stdout)
+        self.assertIn('SKIP_CLAW_PRE_PUSH_BUILD=1', result.stderr)
+        self.assertIn('skipping cargo workspace build', result.stderr)
+
+    def test_default_build_gate_uses_workspace_locked_cargo_build(self) -> None:
+        hook = PRE_PUSH_HOOK.read_text()
+
+        self.assertIn(
+            'cargo build --manifest-path rust/Cargo.toml --workspace --locked',
+            hook,
+        )
+        self.assertIn(
+            'build_cmd=(cargo build --manifest-path rust/Cargo.toml --workspace --locked)',
+            hook,
+        )
+
+
+if __name__ == '__main__':
+    unittest.main()