fix(parity): hermetic live-remote master reads under pytest (Closes #610)

Remediate PR #788 review F1/F2: suite-wide hermetic mode prevents
git ls-remote from running in tests so feature worktrees no longer flip
legacy runtime-context assertions to live_stale, and unit tests stay offline.
Module flag survives patch.dict(clear=True); env override still wins.

Co-Authored-By: Grok 4.5 <[email protected]>

master_parity_gate.py

@@ -32,11 +32,32 @@ import time
 _REMOTE_HEAD_CACHE: dict[tuple[str, str, str], tuple[float, str | None]] = {}
 _REMOTE_HEAD_TTL = 60.0
 
+# When True, ``read_remote_master_head`` never performs ``git ls-remote`` unless
+# ``GITEA_TEST_LIVE_REMOTE_HEAD`` is set. Conftest enables this suite-wide so
+# feature worktrees (whose HEAD differs from live master) cannot flip legacy
+# runtime-context assertions to live_stale, and so unit tests never depend on
+# a live network (PR #788 F1/F2 / issue #610). Module-level (not env-only) so
+# ``patch.dict(os.environ, …, clear=True)`` cannot re-enable the probe.
+_HERMETIC_TEST_MODE: bool = False
+
 
 def _clear_remote_head_cache() -> None:
     """Reset the live-remote head cache (test isolation / forced refresh)."""
     _REMOTE_HEAD_CACHE.clear()
 
+
+def set_hermetic_test_mode(enabled: bool) -> None:
+    """Enable or disable suite-wide hermetic live-remote reads (tests only)."""
+    global _HERMETIC_TEST_MODE
+    _HERMETIC_TEST_MODE = bool(enabled)
+    _clear_remote_head_cache()
+
+
+def hermetic_test_mode() -> bool:
+    """Return whether hermetic live-remote reads are active."""
+    return bool(_HERMETIC_TEST_MODE)
+
+
 # Environment escape hatches (ops + tests):
 #   GITEA_MCP_DISABLE_PARITY_GATE  -> disable enforcement entirely (fail open).
 #   GITEA_TEST_CURRENT_HEAD        -> force the "current" HEAD read, for tests.
@@ -44,6 +65,9 @@ ENV_DISABLE = "GITEA_MCP_DISABLE_PARITY_GATE"
 ENV_TEST_CURRENT_HEAD = "GITEA_TEST_CURRENT_HEAD"
 # GITEA_TEST_LIVE_REMOTE_HEAD -> force the live remote master read, for tests.
 ENV_TEST_LIVE_REMOTE_HEAD = "GITEA_TEST_LIVE_REMOTE_HEAD"
+# GITEA_TEST_ALLOW_LIVE_REMOTE_PROBE -> opt a single test into a real ls-remote
+# even when hermetic mode is on (rare; prefer ENV_TEST_LIVE_REMOTE_HEAD).
+ENV_TEST_ALLOW_LIVE_REMOTE_PROBE = "GITEA_TEST_ALLOW_LIVE_REMOTE_PROBE"
 
 
 def read_git_head(root: str) -> str | None:
@@ -92,10 +116,28 @@ def read_remote_master_head(
     gate does not run a network probe on every mutation/read (``ttl=0`` forces
     a live probe). Both hits and ``None`` misses are cached to bound offline
     latency; the env override bypasses the cache and the subprocess entirely.
+
+    Under suite hermetic mode (``set_hermetic_test_mode(True)``, set by
+    conftest) a missing override returns ``None`` without network I/O so
+    feature-worktree test runs cannot observe live_stale against real master
+    (PR #788 F1) and unit tests stay offline (F2). Opt out with an explicit
+    ``GITEA_TEST_LIVE_REMOTE_HEAD`` pin or ``GITEA_TEST_ALLOW_LIVE_REMOTE_PROBE``.
     """
     forced = os.environ.get(ENV_TEST_LIVE_REMOTE_HEAD)
     if forced is not None:
         return forced.strip() or None
+    if _HERMETIC_TEST_MODE and not (
+        os.environ.get(ENV_TEST_ALLOW_LIVE_REMOTE_PROBE) or ""
+    ).strip():
+        # Hermetic default: live head unknown. live_stale stays False;
+        # mutation_safe is False when live is unknown (documented #610 note).
+        return None
+    # Defense in depth: even without the module flag, never probe while pytest
+    # is running unless the test opted into a real probe or set an override.
+    if (os.environ.get("PYTEST_CURRENT_TEST") or "").strip() and not (
+        os.environ.get(ENV_TEST_ALLOW_LIVE_REMOTE_PROBE) or ""
+    ).strip():
+        return None
     if not root:
         return None
     key = (root, remote, branch)