fix(references): filter user messages in ai-chat onValidateMessages

Author: ericallam

references/ai-chat/src/trigger/chat.ts

@@ -232,15 +232,26 @@ export const aiChat = chat
         turn,
         count: messages.length,
       });
-      // Cast: `chatTools` has executes (output types are real), but
-      // `ChatUiMessage` is derived from the schema-only set in
-      // `chat-tools-schemas.ts` so its tools have `output: never`.
-      // `validateUIMessages` only reads `inputSchema` at runtime, so
-      // the type narrowing is safely sidestepped.
-      return validateUIMessages({
-        messages,
-        tools: chatTools as unknown as Parameters<typeof validateUIMessages>[0]["tools"],
-      });
+      // HITL continuations (`addToolOutput` / `addToolApproveResponse`)
+      // ship a slim assistant on the wire — `state` + `output` /
+      // `errorText` / `approval` only, no `input` or other parts.
+      // `validateUIMessages` rejects that shape (the AI SDK schema
+      // requires `input` on resolved tool parts), so filter to user
+      // messages first. The agent's per-turn merge restores the
+      // hydrated entry's `input` before `toModelMessages`.
+      const userMessages = messages.filter((m) => m.role === "user");
+      if (userMessages.length > 0) {
+        await validateUIMessages({
+          messages: userMessages,
+          // Cast: `chatTools` has executes (output types are real), but
+          // `ChatUiMessage` is derived from the schema-only set in
+          // `chat-tools-schemas.ts` so its tools have `output: never`.
+          // `validateUIMessages` only reads `inputSchema` at runtime, so
+          // the type narrowing is safely sidestepped.
+          tools: chatTools as unknown as Parameters<typeof validateUIMessages>[0]["tools"],
+        });
+      }
+      return messages;
     },
     // #endregion