Assistant: suppress repeated render-tool calls

After the client returns a render tool's result, the model sometimes
re-issues the identical call with a fresh id on the follow-up run,
painting a second copy of the spending-summary card (observed live on
MAF 1.10 / CK 1.62). DeduplicateToolCallMiddleware now tracks which
render tools already ran in the current user turn and drops repeats —
their streamed TOOL_CALL_* events and their entries in the run's
MESSAGES_SNAPSHOT. The system prompt also tells the model the card is
already displayed once its "ok" result is present.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/agent/agent.py

@@ -56,6 +56,9 @@ Generative UI — render tools:
   nothing. The rendered card IS the complete response. Any text you write in
   the same message as a render call will appear as a duplicate below the
   card, which is wrong.
+- When a render_spending_summary tool result ("ok") is already present for
+  the current question, the card is already on screen. Do NOT call the tool
+  again and do NOT add text — end your response with no further output.
 """
 
 

frontend/server.ts

@@ -120,6 +120,27 @@ class DeduplicateToolCallMiddleware extends (Middleware as any) {
     const open = new Set<string>();   // tool call IDs currently in progress
     const closed = new Set<string>(); // tool call IDs that already received END
 
+    // Render tools are display-once: after the client returns their result,
+    // the model sometimes re-issues the same call (fresh id) on the
+    // follow-up run, painting a second identical card. Track which render
+    // tools already ran in the current user turn (from the request's own
+    // message history) and suppress repeats — both their streamed events
+    // and their entries in this run's MESSAGES_SNAPSHOT.
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const inputMessages: any[] = Array.isArray(input?.messages) ? input.messages : [];
+    let lastUserIdx = -1;
+    inputMessages.forEach((m, i) => { if (m?.role === "user") lastUserIdx = i; });
+    const renderedThisTurn = new Set<string>();
+    for (const m of inputMessages.slice(lastUserIdx + 1)) {
+      const calls = m?.toolCalls ?? m?.tool_calls;
+      if (m?.role !== "assistant" || !Array.isArray(calls)) continue;
+      for (const tc of calls) {
+        const name = tc?.function?.name;
+        if (name && RENDER_TOOLS.has(name)) renderedThisTurn.add(name);
+      }
+    }
+    const suppressed = new Set<string>(); // toolCallIds of dropped repeats
+
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     return new Observable<any>((observer) => {
       // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -132,13 +153,51 @@ class DeduplicateToolCallMiddleware extends (Middleware as any) {
 
           if (type === EventType.TOOL_CALL_START) {
             if (!id || closed.has(id) || open.has(id)) return; // duplicate
+            const name: string | undefined = event?.toolCallName;
+            if (name && RENDER_TOOLS.has(name)) {
+              if (renderedThisTurn.has(name)) {
+                suppressed.add(id);
+                return; // repeat render call — drop the whole call
+              }
+              renderedThisTurn.add(name);
+            }
             open.add(id);
           } else if (type === EventType.TOOL_CALL_ARGS || type === EventType.TOOL_CALL_END) {
+            if (id && suppressed.has(id)) return;
             if (id && closed.has(id)) return; // already completed, drop
             if (type === EventType.TOOL_CALL_END && id) {
               open.delete(id);
               closed.add(id);
             }
+          } else if (type === EventType.MESSAGES_SNAPSHOT && suppressed.size > 0) {
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            const msgs: any[] = Array.isArray(event?.messages) ? event.messages : [];
+            const cleaned = msgs
+              // eslint-disable-next-line @typescript-eslint/no-explicit-any
+              .map((m: any) => {
+                const calls = m?.toolCalls ?? m?.tool_calls;
+                if (m?.role !== "assistant" || !Array.isArray(calls)) return m;
+                // eslint-disable-next-line @typescript-eslint/no-explicit-any
+                const kept = calls.filter((tc: any) => !suppressed.has(String(tc?.id ?? "")));
+                if (kept.length === calls.length) return m;
+                const { toolCalls: _a, tool_calls: _b, ...rest } = m;
+                return kept.length > 0 ? { ...rest, toolCalls: kept } : rest;
+              })
+              // eslint-disable-next-line @typescript-eslint/no-explicit-any
+              .filter((m: any) => {
+                if (m?.role === "tool" && suppressed.has(String(m?.toolCallId ?? m?.tool_call_id ?? ""))) {
+                  return false;
+                }
+                if (m?.role === "assistant") {
+                  const calls = m?.toolCalls ?? m?.tool_calls;
+                  const hasCalls = Array.isArray(calls) && calls.length > 0;
+                  const hasText = typeof m?.content === "string" && m.content.length > 0;
+                  if (!hasCalls && !hasText) return false;
+                }
+                return true;
+              });
+            observer.next({ ...event, messages: cleaned });
+            return;
           }
 
           observer.next(event); // emit raw BaseEvent