fix(guard): pin session-state authority and reject direct-import mutation (#695)

Close remaining AC1/AC2/AC6-8 gaps after REQUEST_CHANGES and the PR #701
recurrence: GITEA_ALLOW_DIRECT_MCP_IMPORT never authorizes mutations;
production transport bind pins GITEA_MCP_SESSION_STATE_DIR so redirected
dirs cannot forge independent decision locks; mark/submit fail closed
offline; quarantine continues to void contaminated merge eligibility.

Regression tests reproduce the PR #701 direct-import + state-dir override
sequence. Full suite: 2665 passed, 6 skipped.

Closes #695 (remediation on PR #696)

tests/conftest.py

@@ -58,6 +58,17 @@ def _reset_mutation_authority(monkeypatch):
             _fallback: str = state_dir,
             _env_key: str = mcp_session_state.STATE_DIR_ENV,
         ) -> str:
+            # #695 AC2: when production native transport has pinned a session
+            # state root, that pin is authoritative even under test isolation
+            # (PR #701 redirected-state regression).
+            try:
+                import mcp_daemon_guard
+
+                pinned = mcp_daemon_guard.pinned_session_state_dir()
+                if pinned:
+                    return pinned
+            except Exception:
+                pass
             raw = (os.environ.get(_env_key) or "").strip()
             return raw or _fallback