fix(mcp): unified grant revocation with per-agent tool group isolation

- Add GrantChecker interface with cache + event-bus invalidation for revalidating MCP tool grants at execution time (not just dispatch)
- Move toolGroups from package-level global to per-Registry field; Clone() gives each agent Loop isolated tool groups, eliminating cross-agent race condition
- BridgeTool.Execute rechecks grant validity before executing MCP methods; uses serverID field for cache key
- Wire MCPGrantChecker through ResolverDeps to MCP Manager and LoopConfig
- Add integration test for grant revocation scenarios
- Update policy functions to accept *Registry parameter

cmd/gateway_managed.go

@@ -127,8 +127,10 @@ func wireExtras(
 
 	// 5. Shared MCP connection pool (eliminates duplicate connections across agents)
 	var mcpPool *mcpbridge.Pool
+	var mcpGrantChecker mcpbridge.GrantChecker
 	if stores.MCP != nil {
 		mcpPool = mcpbridge.NewPool(mcpbridge.DefaultPoolConfig())
+		mcpGrantChecker = mcpbridge.NewStoreGrantChecker(stores.MCP, msgBus)
 	}
 
 	// 6. Set up agent resolver: lazy-creates Loops from DB
@@ -221,6 +223,7 @@ func wireExtras(
 		BuiltinToolStore:       stores.BuiltinTools,
 		MCPStore:               stores.MCP,
 		MCPPool:                mcpPool,
+		MCPGrantChecker:        mcpGrantChecker,
 		ConfigPermStore:        stores.ConfigPermissions,
 		MediaStore:             mediaStore,
 		ModelPricing:           appCfg.Telemetry.ModelPricing,