fix(agent): resolve followup message failure after frontend tool calls

Fix Bedrock ValidationException ("Expected toolResult blocks") that occurred on
follow-up messages after using shared state (Canvas/Todos). The root cause was
that _fix_messages_for_bedrock deduplicated ToolMessages by dropping the
placeholder (correct position, adjacent to AI message) and keeping the real
result (wrong position, appended at end). Bedrock requires toolResult blocks
immediately after their corresponding toolUse.

Three fixes in copilotkit_lg_middleware.py:
- Dedup now replaces placeholder in-place with real result, preserving position
- Unanswered tool_call detection uses adjacency check instead of global lookup
- Orphan ToolMessages are cleaned up after stripping tool_calls

Also adds app mode UI (Chat/App toggle), error handling in agent entrypoint,
and None-event filtering.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

copilotkit/copilotkit_lg_middleware.py

@@ -107,24 +107,24 @@ def _fix_messages_for_bedrock(messages: list) -> list:
                         and _INTERRUPTED_PAT.match(messages[i].content))
             ]
             interrupted_indices = [i for i in indices if i not in real_indices]
-            if real_indices:
-                # Drop all interrupted placeholders; keep real (last wins if >1)
-                drop_indices.update(interrupted_indices)
-                drop_indices.update(real_indices[:-1])  # keep only last real
+            if real_indices and interrupted_indices:
+                # Replace the first placeholder (correct position, adjacent to AI
+                # message) with the last real result (likely appended at the end).
+                # This keeps the tool result in the right position for Bedrock.
+                messages[interrupted_indices[0]] = messages[real_indices[-1]]
+                drop_indices.update(interrupted_indices[1:])
+                drop_indices.update(real_indices)  # drop all originals (we moved one)
+            elif real_indices:
+                # No placeholders, multiple real — keep only the last
+                drop_indices.update(real_indices[:-1])
             else:
                 # All interrupted — keep only the last
                 drop_indices.update(interrupted_indices[:-1])
 
         if drop_indices:
             messages[:] = [msg for i, msg in enumerate(messages) if i not in drop_indices]
 
-        # Collect all tool_call_ids that have a ToolMessage answer
-        answered_tc_ids = {
-            m.tool_call_id for m in messages
-            if isinstance(m, ToolMessage) and hasattr(m, 'tool_call_id')
-        }
-
-        for msg in messages:
+        for idx, msg in enumerate(messages):
             if not isinstance(msg, AIMessage):
                 continue
 
@@ -152,11 +152,23 @@ def _fix_messages_for_bedrock(messages: list) -> list:
             if not tool_calls:
                 continue
 
-            # 2. Strip unanswered tool_calls (no matching ToolMessage)
-            unanswered = [tc for tc in tool_calls if tc.get('id') not in answered_tc_ids]
+            # 2. Strip unanswered tool_calls — only consider ToolMessages that
+            #    are ADJACENT (immediately following this AIMessage, before the
+            #    next non-ToolMessage). A ToolMessage at the wrong position
+            #    won't satisfy Bedrock's Converse API requirement that toolResult
+            #    blocks appear in the user turn right after the assistant turn.
+            adjacent_tc_ids: set = set()
+            j = idx + 1
+            while j < len(messages) and isinstance(messages[j], ToolMessage):
+                tc_id = getattr(messages[j], 'tool_call_id', None)
+                if tc_id:
+                    adjacent_tc_ids.add(tc_id)
+                j += 1
+
+            unanswered = [tc for tc in tool_calls if tc.get('id') not in adjacent_tc_ids]
             if unanswered:
                 unanswered_ids = {tc['id'] for tc in unanswered}
-                msg.tool_calls = [tc for tc in tool_calls if tc.get('id') in answered_tc_ids]
+                msg.tool_calls = [tc for tc in tool_calls if tc.get('id') in adjacent_tc_ids]
 
                 # Also strip matching content blocks
                 if isinstance(msg.content, list):
@@ -188,6 +200,22 @@ def _fix_messages_for_bedrock(messages: list) -> list:
                         elif inp is None:
                             block['input'] = {}
 
+        # 5. Remove orphan ToolMessages whose tool_call_id no longer matches
+        #    any remaining tool_call in any AIMessage. These can be left over
+        #    after stripping unanswered tool_calls above.
+        remaining_tc_ids: set = set()
+        for msg in messages:
+            if isinstance(msg, AIMessage):
+                for tc in (getattr(msg, 'tool_calls', None) or []):
+                    tc_id = tc.get('id')
+                    if tc_id:
+                        remaining_tc_ids.add(tc_id)
+        messages[:] = [
+            msg for msg in messages
+            if not isinstance(msg, ToolMessage)
+            or getattr(msg, 'tool_call_id', None) in remaining_tc_ids
+        ]
+
         return messages
 
     async def awrap_model_call(

frontend/src/components/chat/CopilotChatInterface.tsx

@@ -2,29 +2,61 @@
 "use client"
 
 import { useEffect, useState } from "react"
-import { CopilotChat, CopilotKitProvider } from "@copilotkit/react-core/v2"
+import { CopilotChat, CopilotKitProvider, useFrontendTool } from "@copilotkit/react-core/v2"
 import { useAuth as useOidcAuth } from "react-oidc-context"
 import { loadAwsConfig, type AwsExportsConfig } from "@/lib/runtime-config"
 import { useExampleSuggestions } from "@/hooks/useExampleSuggestions"
 import { useCopilotExamples } from "@/hooks/useCopilotExamples"
 import { ThemeProvider } from "@/hooks/useTheme"
 import { TodoCanvas } from "@/components/canvas/TodoCanvas"
+import { ModeToggle } from "@/components/ui/mode-toggle"
 
 const COPILOTKIT_AGENT_ID = "default"
 
 function CopilotChatContent() {
+  const [mode, setMode] = useState<"chat" | "app">("chat")
+
   useExampleSuggestions()
   useCopilotExamples()
 
+  useFrontendTool({
+    name: "enableAppMode",
+    description: "Enable app mode when working with the todo canvas.",
+    handler: async () => {
+      setMode("app")
+    },
+  })
+
+  useFrontendTool({
+    name: "enableChatMode",
+    description: "Enable chat mode",
+    handler: async () => {
+      setMode("chat")
+    },
+  })
+
   return (
-    <div className="h-full flex">
-      {/* Chat pane — takes remaining width */}
-      <div className="flex-1 min-w-0 [&_.copilotKitChat]:h-full [&_.copilotKitChat]:border-0 [&_.copilotKitChat]:shadow-none">
+    <div className="h-full flex flex-row">
+      <ModeToggle mode={mode} onModeChange={setMode} />
+      <div
+        className={`max-h-full overflow-y-auto [&_.copilotKitChat]:h-full [&_.copilotKitChat]:border-0 [&_.copilotKitChat]:shadow-none ${
+          mode === "app"
+            ? "w-1/3 px-6 max-lg:hidden"
+            : "flex-1 px-4 lg:px-6"
+        }`}
+      >
         <CopilotChat agentId={COPILOTKIT_AGENT_ID} className="h-full" />
       </div>
-      {/* Canvas pane — always visible, shows empty state when no todos exist */}
-      <div className="w-2/5 border-l border-gray-200 dark:border-zinc-700">
-        <TodoCanvas />
+      <div
+        className={`h-full overflow-hidden ${
+          mode === "app"
+            ? "w-2/3 border-l dark:border-zinc-700 max-lg:w-full max-lg:border-l-0"
+            : "w-0 border-l-0"
+        }`}
+      >
+        <div className="h-full w-full lg:w-[66.666vw]">
+          <TodoCanvas />
+        </div>
       </div>
     </div>
   )

frontend/src/components/ui/mode-toggle.tsx

@@ -0,0 +1,39 @@
+interface ModeToggleProps {
+  mode: "chat" | "app"
+  onModeChange: (mode: "chat" | "app") => void
+}
+
+export function ModeToggle({ mode, onModeChange }: ModeToggleProps) {
+  return (
+    <div className="fixed top-4 right-4 z-50 flex bg-gray-100 dark:bg-zinc-800 rounded-lg p-1 shadow-sm max-lg:top-2 max-lg:right-2 max-lg:scale-90">
+      <button
+        onClick={() => onModeChange("chat")}
+        className={`
+          px-4 py-2 rounded-md text-sm font-medium transition-all max-lg:px-3 max-lg:py-1.5 max-lg:text-xs
+          cursor-pointer
+          ${
+            mode === "chat"
+              ? "bg-white dark:bg-zinc-700 text-gray-900 dark:text-white shadow-sm"
+              : "text-gray-600 dark:text-zinc-400 hover:text-gray-900 dark:hover:text-white"
+          }
+        `}
+      >
+        Chat
+      </button>
+      <button
+        onClick={() => onModeChange("app")}
+        className={`
+          px-4 py-2 rounded-md text-sm font-medium transition-all max-lg:px-3 max-lg:py-1.5 max-lg:text-xs
+          cursor-pointer
+          ${
+            mode === "app"
+              ? "bg-white dark:bg-zinc-700 text-gray-900 dark:text-white shadow-sm"
+              : "text-gray-600 dark:text-zinc-400 hover:text-gray-900 dark:hover:text-white"
+          }
+        `}
+      >
+        App Mode
+      </button>
+    </div>
+  )
+}

patterns/langgraph-single-agent/langgraph_agent.py

@@ -7,7 +7,9 @@
 import json
 import os
 import traceback
-from ag_ui.core import RunAgentInput
+import logging
+
+from ag_ui.core import RunAgentInput, RunErrorEvent, RunFinishedEvent
 from bedrock_agentcore.identity.auth import requires_access_token
 from bedrock_agentcore.runtime import BedrockAgentCoreApp, RequestContext
 from copilotkit import CopilotKitMiddleware, LangGraphAGUIAgent
@@ -184,8 +186,16 @@ async def invocations(payload: dict, context: RequestContext):
         config={"configurable": {"actor_id": actor_id}},
     )
 
-    async for event in request_agent.run(input_data):
-        yield event.model_dump(mode="json", by_alias=True, exclude_none=True)
+    try:
+        async for event in request_agent.run(input_data):
+            if event is not None:
+                yield event.model_dump(mode="json", by_alias=True, exclude_none=True)
+    except Exception as exc:
+        logging.exception("Agent run failed")
+        yield RunErrorEvent(
+            message=str(exc) or type(exc).__name__,
+            code=type(exc).__name__,
+        ).model_dump(mode="json", by_alias=True, exclude_none=True)
 
 
 if __name__ == "__main__":