fix: notify on flow restore and resource changes, address review nits

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

backend/migrations/20260924065755_mcp_tools_change_notify.down.sql

@@ -1,6 +1,9 @@
 DROP TRIGGER IF EXISTS script_mcp_tools_update_trigger ON script;
 DROP TRIGGER IF EXISTS script_mcp_tools_delete_trigger ON script;
+DROP TRIGGER IF EXISTS flow_mcp_tools_insert_trigger ON flow;
 DROP TRIGGER IF EXISTS flow_mcp_tools_update_trigger ON flow;
+DROP TRIGGER IF EXISTS resource_mcp_tools_insert_delete_trigger ON resource;
+DROP TRIGGER IF EXISTS resource_mcp_tools_rename_trigger ON resource;
 DROP TRIGGER IF EXISTS flow_mcp_tools_delete_trigger ON flow;
 DROP TRIGGER IF EXISTS favorite_mcp_tools_insert_trigger ON favorite;
 DROP TRIGGER IF EXISTS favorite_mcp_tools_delete_trigger ON favorite;

backend/migrations/20260924065755_mcp_tools_change_notify.up.sql

@@ -1,5 +1,5 @@
--- Deploys already emit `notify_runnable_version_change`; these cover the other changes to the
--- scripts and flows the MCP server lists as tools. One event per workspace per transaction:
+-- Deploys already emit `notify_runnable_version_change`; these cover the other changes to what
+-- the MCP server lists as tools. One event per workspace per transaction:
 -- archiving a path touches every version of it and deleting a workspace every script, while the
 -- poll loop reads 1000 events per tick, so a row-level burst would delay every other channel.
 CREATE OR REPLACE FUNCTION notify_mcp_tools_change()
@@ -27,6 +27,14 @@ AFTER DELETE ON script
 FOR EACH ROW
 EXECUTE FUNCTION notify_mcp_tools_change();
 
+-- A create inserts the row with no versions and appends one later, which the versions trigger
+-- sees. Restore from trash, rename and fork insert the row with its versions already set.
+CREATE TRIGGER flow_mcp_tools_insert_trigger
+AFTER INSERT ON flow
+FOR EACH ROW
+WHEN (cardinality(NEW.versions) > 0)
+EXECUTE FUNCTION notify_mcp_tools_change();
+
 CREATE TRIGGER flow_mcp_tools_update_trigger
 AFTER UPDATE OF archived ON flow
 FOR EACH ROW
@@ -38,6 +46,18 @@ AFTER DELETE ON flow
 FOR EACH ROW
 EXECUTE FUNCTION notify_mcp_tools_change();
 
+-- A tool's input schema lists the workspace's resources of each resource type it takes.
+CREATE TRIGGER resource_mcp_tools_insert_delete_trigger
+AFTER INSERT OR DELETE ON resource
+FOR EACH ROW
+EXECUTE FUNCTION notify_mcp_tools_change();
+
+CREATE TRIGGER resource_mcp_tools_rename_trigger
+AFTER UPDATE OF path ON resource
+FOR EACH ROW
+WHEN (OLD.path IS DISTINCT FROM NEW.path)
+EXECUTE FUNCTION notify_mcp_tools_change();
+
 -- Favorites are the tool list of an `mcp:favorites` token.
 CREATE TRIGGER favorite_mcp_tools_insert_trigger
 AFTER INSERT ON favorite

backend/src/main.rs

@@ -1876,8 +1876,10 @@ async fn process_notify_event(
             );
             windmill_common::workspaces::PUBLIC_APP_RATE_LIMIT_CACHE.remove(payload);
         }
-        #[cfg(feature = "mcp")]
-        "notify_mcp_tools_change" => windmill_api::notify_mcp_tools_changed(payload),
+        "notify_mcp_tools_change" => {
+            #[cfg(feature = "mcp")]
+            windmill_api::notify_mcp_tools_changed(payload);
+        }
         "notify_runnable_version_change" => {
             tracing::info!("Runnable version change detected: {}", payload);
             match payload.split(':').collect::<Vec<&str>>().as_slice() {

backend/windmill-api/src/lib.rs

@@ -77,8 +77,6 @@ mod ai_shared_artifacts;
 mod apps;
 mod apps_raw_bundle;
 pub use apps::invalidate_app_policy_cache;
-#[cfg(feature = "mcp")]
-pub use windmill_mcp::server::notify_tools_changed as notify_mcp_tools_changed;
 pub mod args;
 mod audit;
 pub mod auth;
@@ -211,6 +209,8 @@ mod mcp_tools;
 
 #[cfg(feature = "mcp")]
 mod mcp;
+#[cfg(feature = "mcp")]
+pub use windmill_mcp::server::notify_tools_changed as notify_mcp_tools_changed;
 #[cfg(all(feature = "mcp", feature = "private"))]
 mod mcp_oauth_ee;
 #[cfg(feature = "mcp")]

backend/windmill-mcp/src/server/runner.rs

@@ -57,16 +57,19 @@ const LIST_TTL_MS: u64 = 0;
 /// cache entry would leak one token's view to another.
 const LIST_CACHE_SCOPE: CacheScope = CacheScope::Private;
 
-/// Workspaces whose listed scripts or flows changed. Fed from the notify-event
-/// poll loop, so a change committed through any replica reaches the listen
-/// streams held by every replica.
+/// Workspaces whose tool listing changed. Fed from the notify-event poll loop, so
+/// a change committed through any replica reaches the listen streams held by
+/// every replica. Sized well past the poll loop's 1000-event batch: a lagged
+/// receiver notifies, and every stream on the instance would re-list at once.
 static TOOLS_CHANGED: LazyLock<broadcast::Sender<String>> =
-    LazyLock::new(|| broadcast::channel(1024).0);
+    LazyLock::new(|| broadcast::channel(8192).0);
 
 /// A poll batch delivers all of its events back to back; waiting this long before
 /// notifying folds a bulk change into one `list_changed` per stream.
 const TOOLS_CHANGED_COALESCE: Duration = Duration::from_secs(1);
 
+/// Wake the `subscriptions/listen` streams of `workspace_id` on this process.
+/// Fire-and-forget: with no stream open, the event is dropped.
 pub fn notify_tools_changed(workspace_id: &str) {
     let _ = TOOLS_CHANGED.send(workspace_id.to_string());
 }
@@ -465,10 +468,10 @@ impl<B: McpBackend> ServerHandler for Runner<B> {
         Cow::Borrowed(SUPPORTED_PROTOCOL_VERSIONS)
     }
 
-    /// Only the pre-2026-07-28 revisions reach `initialize`, and they have no stream
-    /// to receive `list_changed` on (legacy sessions are off and
-    /// `subscriptions/listen` is 2026-07-28 only), so the capability is withdrawn
-    /// here. It stays in `get_info`, which bounds what a listen filter may accept.
+    /// A pre-2026-07-28 revision has no stream to receive `list_changed` on (legacy
+    /// sessions are off and `subscriptions/listen` is 2026-07-28 only), so the
+    /// capability is withdrawn when one is negotiated. It stays in `get_info`, which
+    /// bounds what a listen filter may accept.
     async fn initialize(
         &self,
         request: InitializeRequestParams,
@@ -479,8 +482,10 @@ impl<B: McpBackend> ServerHandler for Runner<B> {
         if SUPPORTED_PROTOCOL_VERSIONS.contains(&request.protocol_version) {
             info.protocol_version = request.protocol_version;
         }
-        if let Some(tools) = info.capabilities.tools.as_mut() {
-            tools.list_changed = None;
+        if info.protocol_version != ProtocolVersion::V_2026_07_28 {
+            if let Some(tools) = info.capabilities.tools.as_mut() {
+                tools.list_changed = None;
+            }
         }
         Ok(info)
     }