* feat(mcp): filter tools at registration + detect FastMCP session reset with force-reconnect
Two foundational MCP reliability improvements:
(1) Tool allow/deny filtering at BridgeTool registration: Previously the runtime grant-check at execute time surfaced "grant revoked" errors when the LLM called a tool it wasn't allowed to call. Filter upfront in both the per-agent registration path (manager_connect.go) and per-user registration path (loop_mcp_user.go). Adds tool_filter.go with IsToolAllowed + tests. This eliminates the "registered then runtime-denied" loop.
(2) FastMCP session reset detection + force-reconnect: FastMCP/Python mcp servers reject tools/call as "invalid during session initialization" when the upstream session lifecycle resets but our pool still holds the old Mcp-Session-Id. Detector matches three known phrasings (FastMCP, mcp-go, mcp-go transport ErrSessionTerminated) in session_reset.go. On detection, BridgeTool.Execute requests a force-reconnect via atomic CAS dedup so N concurrent failing calls collapse to one reconnect. Health loops skip ping while pending so a server answering ping in "initializing" state cannot clobber connected=true before the fresh Initialize completes. Includes 30s timeout, structured slog telemetry, concurrent CAS dedup test.
Files: tool_filter.go + tool_filter_test.go (new), session_reset.go + session_reset_test.go (new), manager_connect.go (connectServer/connectViaPool signatures + registerBridgeTools/registerPoolBridgeTools filter logic + reconnPending skip), manager.go (connectAndFilter + connectServer call signature changes), loop_mcp_user.go (filter-at-register block + WithForceReconnect wiring), pool.go (reconnPending skip), bridge_tool.go (session reset detection + WithForceReconnect callback).
* fix(mcp): self-heal grant cache + bypass per-user grant for system/empty userID
Two production fixes for "MCP tool: grant revoked" recurring on song-nhi-v2.
(1) System-user bypass in ListAccessible: Registration uses LoadForAgent(ctx, agentID, "") while execute uses IsAllowed(ctx, agentID, "system", ...). The LEFT JOIN on mcp_user_grants could match a stale disabled row keyed user_id='system' and silently filter the server out only at execute. Skip the join entirely for synthetic owner identities (userID="" or "system") so registration and execute see the same set. Applied to both PostgreSQL (mcp_servers_access.go) and SQLite (mcp_servers_access.go).
(2) Grant-checker no-cache on empty allowByServer: grant_checker.loadEntry now skips the cache write when allowByServer is empty. Without this, a single transient empty result pinned permanent denial until a bus invalidate fired. Re-queries until the empty condition clears, then caches normally. Includes TestStoreGrantChecker_EmptyEntryNotCached.
