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)

mcp_session_state.py

@@ -44,6 +44,34 @@ SESSION_PROFILE_LOCK_ENV = "GITEA_SESSION_PROFILE_LOCK"
 
 
 def default_state_dir() -> str:
+    """Resolve the durable session-state root.
+
+    When production native MCP transport is bound (#695 AC2), the directory
+    pinned at transport bind is authoritative: later overrides of
+    ``GITEA_MCP_SESSION_STATE_DIR`` cannot manufacture a second authority
+    domain (PR #701 recurrence: ``.mcp_session_701`` evasion of cross-PR
+    decision locks).
+    """
+    try:
+        import mcp_daemon_guard
+
+        pinned = mcp_daemon_guard.pinned_session_state_dir()
+        if pinned:
+            return pinned
+    except Exception:
+        # Fail open to env/default only when guard is unavailable (e.g. partial
+        # import during bootstrap). Mutation gates still fail closed separately.
+        pass
+    raw = (os.environ.get(STATE_DIR_ENV) or DEFAULT_STATE_DIR).strip()
+    return raw or DEFAULT_STATE_DIR
+
+
+def env_session_state_dir_unpinned() -> str:
+    """Raw env/default session-state dir ignoring production transport pin.
+
+    Intended for diagnostics and tests that assert pin behavior — not for
+    mutation-sensitive durable proofs under a bound native daemon.
+    """
     raw = (os.environ.get(STATE_DIR_ENV) or DEFAULT_STATE_DIR).strip()
     return raw or DEFAULT_STATE_DIR
 
@@ -362,6 +390,26 @@ def save_state(
             body["org"] = key_org
         if key_repo is not None:
             body["repo"] = key_repo
+        # Stamp session-state authority used for this write (#695 AC2 / AC6).
+        body.setdefault("session_state_dir", root)
+        try:
+            import mcp_daemon_guard
+
+            prov = mcp_daemon_guard.mutation_provenance_fields()
+            body.setdefault(
+                "native_token_fingerprint", prov.get("native_token_fingerprint")
+            )
+            body.setdefault(
+                "native_mcp_transport", bool(prov.get("native_mcp_transport"))
+            )
+            body.setdefault(
+                "production_native_mcp_transport",
+                bool(prov.get("production_native_mcp_transport")),
+            )
+            body.setdefault("transport", prov.get("transport"))
+        except Exception:
+            body.setdefault("native_mcp_transport", False)
+            body.setdefault("transport", "untrusted")
 
         envelope = {
             "kind": kind,
@@ -373,6 +421,8 @@ def save_state(
             "recorded_at": body["recorded_at"],
             "updated_at": body["updated_at"],
             "writer_pid": body["writer_pid"],
+            "session_state_dir": body.get("session_state_dir"),
+            "transport": body.get("transport"),
             "payload": body,
         }
         _write_json(path, envelope)