feat(chat): unify QuickChat backend path and consolidate render toggle

Backend
- chat.ts now routes both regular chat and QuickChat through
  createResolvedAgentSession instead of branching to createFnAgent for
  the no-runtime-hint case. This removes the divergent path where
  pi-ai's cleanupSessionResources(sessionId) could tear down resources
  the next generation depends on.
- sendMessage's finally only disposes the agent if it still owns the
  activeGenerations slot. A newer generation that has pre-empted us
  cleans up its own agent in its own finally — disposing here would
  yank the underlying CLI process out from under it.
- __setCreateFnAgent test helper now mirrors its mock into the
  createResolvedAgentSession slot so existing test setups still work
  after the unification.

Frontend
- Extract createChatStreamHandlers (RAF coalescing, accumulators,
  tool-call dedup, fallback handling) — useChat and useQuickChat were
  duplicating ~85 LOC each. Both now compose the shared factory.
- Move shared chat types into chatTypes.ts. The hooks re-export them
  for backward compatibility with existing consumers.
- Removed per-message Markdown/plain-text eye toggles. A single
  thread-level toggle in the chat header now flips every assistant
  bubble (including the streaming one) between rendered Markdown and
  plain text.
- Model-only chats hide the per-message agent identity row entirely;
  the model name is already in the thread header.

Tests
- Updated ChatView tests to reflect the new render-toggle contract
  (single header toggle drives all bubbles) and the model-only avatar
  suppression.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.changeset/chat-quickchat-unification-and-render-toggle.md

@@ -0,0 +1,9 @@
+---
+"@runfusion/fusion": patch
+---
+
+Fix Quick Chat backend divergence and consolidate the chat render-mode toggle.
+
+- Backend: Quick Chat and regular chat now go through a single agent-creation path (`createResolvedAgentSession`), eliminating the `createFnAgent` branch where pi-ai's `cleanupSessionResources(sessionId)` could tear down resources still in use by a newer generation. The `sendMessage` `finally` only disposes the agent if it still owns the `activeGenerations` slot, so a pre-empted generation no longer rips state out from under its successor.
+- Frontend: extracted the SSE streaming-handler factory shared between `useChat` and `useQuickChat` (RAF coalescing, accumulators, tool-call dedup, fallback handling) into `createChatStreamHandlers`. Both hooks now compose it instead of duplicating ~85 LOC each.
+- UX: removed per-message Markdown/plain-text eye toggles. A single thread-level toggle now lives in the chat header and flips every assistant bubble (including the streaming one) between rendered Markdown and plain text. Model-only chats also drop their per-message agent-identity row — the model is shown once in the thread header.

packages/dashboard/app/components/ChatView.css

@@ -215,10 +215,40 @@
 }
 
 .chat-thread-header-new-chat {
-  margin-left: auto;
   flex-shrink: 0;
 }
 
+/* Single thread-wide markdown / plain-text toggle, anchored to the right of
+ * the header next to "New Chat". Replaces the per-message eye toggle that
+ * used to live inside every assistant bubble. */
+.chat-thread-header-render-toggle {
+  margin-left: auto;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: calc(var(--space-md) * 3);
+  height: calc(var(--space-md) * 3);
+  min-width: calc(var(--space-md) * 3);
+  min-height: calc(var(--space-md) * 3);
+  padding: 0;
+  border: none;
+  border-radius: 4px;
+  color: var(--text-muted);
+  background: transparent;
+  cursor: pointer;
+  outline: none;
+  transition: background var(--transition-fast), color var(--transition-fast);
+}
+
+.chat-thread-header-render-toggle:hover {
+  background: var(--bg-hover, var(--bg-secondary));
+  color: var(--text);
+}
+
+.chat-thread-header-render-toggle--plain {
+  color: var(--text);
+}
+
 /* Messages */
 .chat-messages {
   flex: 1;
@@ -262,6 +292,15 @@
   color: var(--text-secondary);
 }
 
+/* Model-only chats hide the per-message agent identity. The toggle still
+ * needs a place to live, so collapse the avatar row to just the toggle on
+ * the right edge instead of a full identity strip. */
+.chat-message-avatar.chat-message-avatar--toolbar-only {
+  margin-bottom: 0;
+  min-height: 0;
+  justify-content: flex-end;
+}
+
 .chat-message-render-toggle {
   display: inline-flex;
   align-items: center;

packages/dashboard/app/components/ChatView.tsx

@@ -541,13 +541,24 @@ function NewChatDialog({ projectId, onClose, onCreate }: NewChatDialogProps) {
 
 interface ChatMessageItemProps {
   message: ChatMessageInfo;
+  /**
+   * When true, render assistant message content as plain text instead of
+   * Markdown. The per-message eye toggle has been removed in favor of a
+   * single thread-level toggle in the chat header, so this is a global
+   * mirror of that header state.
+   */
   forcePlain: boolean;
   agentName: string;
+  /**
+   * Hide the per-message agent identity (icon + name + model tag) on
+   * assistant bubbles. In model-only chats the agent identity *is* the
+   * active model and it's already shown in the thread header.
+   */
+  hideAssistantIdentity: boolean;
   showAssistantModelTag: boolean;
   activeModelTag: string | null;
   activeSessionId: string | null;
   mentionAgentsByName: Map<string, Agent>;
-  onToggleRender: (id: string) => void;
 }
 
 // Renders a single chat message bubble. Memoized so the streaming bubble's
@@ -557,11 +568,11 @@ const ChatMessageItem = memo(function ChatMessageItem({
   message,
   forcePlain,
   agentName,
+  hideAssistantIdentity,
   showAssistantModelTag,
   activeModelTag,
   activeSessionId,
   mentionAgentsByName,
-  onToggleRender,
 }: ChatMessageItemProps) {
   const isAssistantMessage = message.role === "assistant";
 
@@ -659,20 +670,11 @@ const ChatMessageItem = memo(function ChatMessageItem({
       className={`chat-message chat-message--${message.role}`}
       data-testid={`chat-message-${message.id}`}
     >
-      {isAssistantMessage && (
+      {isAssistantMessage && !hideAssistantIdentity && (
         <div className="chat-message-avatar">
           <Bot size={14} />
           <span>{agentName}</span>
           {showAssistantModelTag && activeModelTag && <span className="chat-model-tag">{activeModelTag}</span>}
-          <button
-            type="button"
-            className={`chat-message-render-toggle${forcePlain ? " chat-message-render-toggle--plain" : ""}`}
-            data-testid="chat-message-render-toggle"
-            aria-label={forcePlain ? "Show rendered markdown" : "Show plain text"}
-            onClick={() => onToggleRender(message.id)}
-          >
-            {forcePlain ? <EyeOff size={14} /> : <Eye size={14} />}
-          </button>
         </div>
       )}
       {isAssistantMessage
@@ -730,7 +732,11 @@ export function ChatView({ projectId, addToast }: ChatViewProps) {
   const [mentionPopupVisible, setMentionPopupVisible] = useState(false);
   const [mentionHighlightIndex, setMentionHighlightIndex] = useState(0);
   const [mentionStartPos, setMentionStartPos] = useState(-1);
-  const [plainTextMessageIds, setPlainTextMessageIds] = useState<Set<string>>(() => new Set());
+  // Single thread-wide toggle: when true, all assistant content (including the
+  // streaming bubble) renders as plain text instead of Markdown. Replaces the
+  // earlier per-message toggle so the chat header owns this control instead
+  // of every reply having its own button.
+  const [showAllAsPlain, setShowAllAsPlain] = useState(false);
   // Attachment state mirrors QuickEntryBox: pending files selected before send.
   const [pendingAttachments, setPendingAttachments] = useState<PendingAttachment[]>([]);
   const [isDragOver, setIsDragOver] = useState(false);
@@ -1479,22 +1485,25 @@ export function ChatView({ projectId, addToast }: ChatViewProps) {
       ? (activeModelTag ?? "Fusion")
       : (activeSession?.agentId?.slice(0, 30) ?? "Fusion"));
 
-  const showAssistantModelTag = Boolean(activeModelTag && activeModelTag !== agentName);
+  // The model tag is already visible in the thread header — repeating it on
+  // every assistant message is noise. Keep it suppressed for regular chat
+  // (real agent name is the identity); QuickChat already collapses the tag
+  // because its `agentName` IS the model tag, so the per-message slot was
+  // always empty there too.
+  const showAssistantModelTag = false;
+
+  // In model-only chats (no real agent picked) the agent identity *is* the
+  // model name, which is already in the thread header. Repeating it on every
+  // assistant bubble is noise. Hide the per-message identity row entirely;
+  // the render-mode toggle still appears in a slim toolbar.
+  const hideAssistantIdentity = activeSession?.agentId === FN_AGENT_ID;
 
   const pendingPreview = pendingMessage.length > 50
     ? `${pendingMessage.slice(0, 50)}…`
     : pendingMessage;
 
-  const toggleMessageRenderMode = useCallback((messageId: string) => {
+  const toggleAllAsPlain = useCallback(() => {
-    setPlainTextMessageIds((current) => {
+    setShowAllAsPlain((value) => !value);
-      const next = new Set(current);
-      if (next.has(messageId)) {
-        next.delete(messageId);
-      } else {
-        next.add(messageId);
-      }
-      return next;
-    });
   }, []);
 
   const renderAssistantContent = useCallback(
@@ -1677,6 +1686,17 @@ export function ChatView({ projectId, addToast }: ChatViewProps) {
             <Bot size={16} />
             <span className="chat-thread-header-title">{threadHeaderTitle}</span>
             {showThreadHeaderModelTag && <span className="chat-model-tag">{activeModelTag}</span>}
+            {hasThreadInView && (
+              <button
+                type="button"
+                className={`chat-thread-header-render-toggle${showAllAsPlain ? " chat-thread-header-render-toggle--plain" : ""}`}
+                data-testid="chat-thread-render-toggle"
+                aria-label={showAllAsPlain ? "Show all messages as rendered Markdown" : "Show all messages as plain text"}
+                onClick={toggleAllAsPlain}
+              >
+                {showAllAsPlain ? <EyeOff size={14} /> : <Eye size={14} />}
+              </button>
+            )}
             {!isMobile && (
               <button
                 className="btn btn-sm btn-primary chat-thread-header-new-chat"
@@ -1699,32 +1719,25 @@ export function ChatView({ projectId, addToast }: ChatViewProps) {
                 <ChatMessageItem
                   key={message.id}
                   message={message}
-                  forcePlain={plainTextMessageIds.has(message.id)}
+                  forcePlain={showAllAsPlain}
                   agentName={agentName}
+                  hideAssistantIdentity={hideAssistantIdentity}
                   showAssistantModelTag={showAssistantModelTag}
                   activeModelTag={activeModelTag}
                   activeSessionId={activeSession?.id ?? null}
                   mentionAgentsByName={mentionAgentsByName}
-                  onToggleRender={toggleMessageRenderMode}
                 />
               ))}
               <div className="chat-message chat-message--assistant chat-message--streaming">
+                {!hideAssistantIdentity && (
                   <div className="chat-message-avatar">
                     <Bot size={14} />
                     <span>{agentName}</span>
                     {showAssistantModelTag && <span className="chat-model-tag">{activeModelTag}</span>}
-                  <button
-                    type="button"
-                    className={`chat-message-render-toggle${plainTextMessageIds.has("__streaming__") ? " chat-message-render-toggle--plain" : ""}`}
-                    data-testid="chat-message-render-toggle"
-                    aria-label={plainTextMessageIds.has("__streaming__") ? "Show rendered markdown" : "Show plain text"}
-                    onClick={() => toggleMessageRenderMode("__streaming__")}
-                  >
-                    {plainTextMessageIds.has("__streaming__") ? <EyeOff size={14} /> : <Eye size={14} />}
-                  </button>
                   </div>
+                )}
                 {streamingText ? (
-                  renderAssistantContent(streamingText, plainTextMessageIds.has("__streaming__"))
+                  renderAssistantContent(streamingText, showAllAsPlain)
                 ) : (
                   <div className="chat-message-content chat-message-content--waiting">
                     {streamingThinking ? "Thinking…" : "Connecting…"}
@@ -1758,13 +1771,13 @@ export function ChatView({ projectId, addToast }: ChatViewProps) {
                 <ChatMessageItem
                   key={message.id}
                   message={message}
-                  forcePlain={plainTextMessageIds.has(message.id)}
+                  forcePlain={showAllAsPlain}
                   agentName={agentName}
+                  hideAssistantIdentity={hideAssistantIdentity}
                   showAssistantModelTag={showAssistantModelTag}
                   activeModelTag={activeModelTag}
                   activeSessionId={activeSession?.id ?? null}
                   mentionAgentsByName={mentionAgentsByName}
-                  onToggleRender={toggleMessageRenderMode}
                 />
               ))}
             </>

packages/dashboard/app/components/__tests__/ChatView.test.tsx

@@ -445,7 +445,7 @@ describe("ChatView", () => {
     expect(screen.queryByTestId("chat-render-mode-plain")).not.toBeInTheDocument();
   });
 
-  it("renders per-message eye toggles for assistant bubbles on desktop and isolates toggles by message", async () => {
+  it("thread-header toggle flips every assistant bubble between rendered Markdown and plain text", async () => {
     setupMockChat({
       activeSession: { id: "session-001", agentId: "agent-001", status: "active", title: "Test Chat", createdAt: "2026-04-08T00:00:00.000Z", updatedAt: "2026-04-08T00:00:00.000Z" },
       messages: [
@@ -458,24 +458,27 @@ describe("ChatView", () => {
 
     const firstBubble = screen.getByTestId("chat-message-msg-001");
     const secondBubble = screen.getByTestId("chat-message-msg-002");
-    const [firstToggle, secondToggle] = screen.getAllByTestId("chat-message-render-toggle");
+    const headerToggle = screen.getByTestId("chat-thread-render-toggle");
 
-    expect(firstToggle).toBeInTheDocument();
+    // Per-message toggles were intentionally removed; only the single
-    expect(secondToggle).toBeInTheDocument();
+    // thread-level toggle should exist.
+    expect(screen.queryAllByTestId("chat-message-render-toggle")).toHaveLength(0);
     expect(within(firstBubble).getByText("First", { selector: "strong" })).toBeInTheDocument();
     expect(within(secondBubble).getByText("Second", { selector: "strong" })).toBeInTheDocument();
 
-    await userEvent.click(firstToggle);
+    await userEvent.click(headerToggle);
 
     expect(within(firstBubble).getByText(/\*\*First\*\* item/)).toBeInTheDocument();
     expect(within(firstBubble).queryByText("First", { selector: "strong" })).toBeNull();
-    expect(within(secondBubble).getByText("Second", { selector: "strong" })).toBeInTheDocument();
+    expect(within(secondBubble).getByText(/\*\*Second\*\* item/)).toBeInTheDocument();
+    expect(within(secondBubble).queryByText("Second", { selector: "strong" })).toBeNull();
 
-    await userEvent.click(firstToggle);
+    await userEvent.click(headerToggle);
     expect(within(firstBubble).getByText("First", { selector: "strong" })).toBeInTheDocument();
+    expect(within(secondBubble).getByText("Second", { selector: "strong" })).toBeInTheDocument();
   });
 
-  it("uses a dedicated streaming toggle sentinel without affecting persisted assistant messages", async () => {
+  it("thread-header toggle also drives the streaming bubble", async () => {
     setupMockChat({
       activeSession: { id: "session-001", agentId: "agent-001", status: "active", title: "Test Chat", createdAt: "2026-04-08T00:00:00.000Z", updatedAt: "2026-04-08T00:00:00.000Z" },
       messages: [{ id: "msg-001", sessionId: "session-001", role: "assistant", content: "**Persisted**", createdAt: "2026-04-08T00:00:00.000Z" }],
@@ -487,19 +490,19 @@ describe("ChatView", () => {
 
     const persistedBubble = screen.getByTestId("chat-message-msg-001");
     const streamingBubble = document.querySelector(".chat-message--streaming") as HTMLElement;
-    const [persistedToggle, streamingToggle] = screen.getAllByTestId("chat-message-render-toggle");
+    const headerToggle = screen.getByTestId("chat-thread-render-toggle");
 
     expect(within(streamingBubble).getByText("Live", { selector: "strong" })).toBeInTheDocument();
     expect(within(persistedBubble).getByText("Persisted", { selector: "strong" })).toBeInTheDocument();
 
-    await userEvent.click(streamingToggle);
+    await userEvent.click(headerToggle);
 
     expect(within(streamingBubble).getByText(/\*\*Live\*\* stream/)).toBeInTheDocument();
-    expect(within(persistedBubble).getByText("Persisted", { selector: "strong" })).toBeInTheDocument();
-
-    await userEvent.click(persistedToggle);
     expect(within(persistedBubble).getByText(/\*\*Persisted\*\*/)).toBeInTheDocument();
-    expect(within(streamingBubble).getByText(/\*\*Live\*\* stream/)).toBeInTheDocument();
+
+    await userEvent.click(headerToggle);
+    expect(within(streamingBubble).getByText("Live", { selector: "strong" })).toBeInTheDocument();
+    expect(within(persistedBubble).getByText("Persisted", { selector: "strong" })).toBeInTheDocument();
   });
 
   it("renders tool calls from persisted messages", () => {
@@ -869,7 +872,10 @@ describe("ChatView", () => {
     expect(within(avatar!).queryByText("Fusion")).not.toBeInTheDocument();
   });
 
-  it("shows Fusion in assistant message avatar for fn agent sessions", () => {
+  it("hides per-message assistant identity for fn agent (model-only) sessions", () => {
+    // Model-only chats use the active model as their identity, which is
+    // already shown in the thread header. We deliberately suppress the
+    // per-message avatar to avoid repeating it on every reply.
     setupMockChat({
       activeSession: { id: "session-001", agentId: "__fn_agent__", status: "active", title: "Fusion Chat", createdAt: "2026-04-08T00:00:00.000Z", updatedAt: "2026-04-08T00:00:00.000Z" },
       messages: [
@@ -879,12 +885,11 @@ describe("ChatView", () => {
 
     render(<ChatView projectId="proj-123" addToast={vi.fn()} />);
 
-    const avatar = document.querySelector(".chat-message-avatar") as HTMLElement | null;
+    const messageBubble = screen.getByTestId("chat-message-msg-001");
-    expect(avatar).toBeInTheDocument();
+    expect(messageBubble.querySelector(".chat-message-avatar")).toBeNull();
-    expect(within(avatar!).getByText("Fusion")).toBeInTheDocument();
   });
 
-  it("shows formatted model name in assistant message avatar for fn agent sessions", async () => {
+  it("hides per-message assistant identity for fn agent (model-only) sessions even when a model is configured", async () => {
     setupMockChat({
       activeSession: {
         id: "session-001",
@@ -902,14 +907,12 @@ describe("ChatView", () => {
 
     render(<ChatView projectId="proj-123" addToast={vi.fn()} />);
 
-    const avatar = document.querySelector(".chat-message-avatar") as HTMLElement | null;
+    const messageBubble = screen.getByTestId("chat-message-msg-001");
-    expect(avatar).toBeInTheDocument();
+    expect(messageBubble.querySelector(".chat-message-avatar")).toBeNull();
-
+    // The model name still appears once in the thread header.
     await waitFor(() => {
-      expect(within(avatar!).getByText("Claude Sonnet 4.5")).toBeInTheDocument();
+      expect(screen.getByText("Claude Sonnet 4.5")).toBeInTheDocument();
     });
-    expect(within(avatar!).queryByText("Fusion")).not.toBeInTheDocument();
-    expect(avatar?.querySelector(".chat-model-tag")).toBeNull();
   });
 
   it("shows resolved agent name in streaming assistant avatar", async () => {
@@ -1858,7 +1861,11 @@ describe("ChatView", () => {
     expect(modelTag).not.toBeInTheDocument();
   });
 
-  it("shows model tag in message avatar when non-fn session has model", () => {
+  it("does not repeat the model tag in per-message avatars for non-fn sessions", () => {
+    // Per-message model tags were intentionally removed — the model is shown
+    // once in the thread header. The avatar should still render with the
+    // agent name (no agent identity collapse for real agents) but no model
+    // tag inside it.
     setupMockChat({
       activeSession: {
         id: "session-001",
@@ -1876,12 +1883,13 @@ describe("ChatView", () => {
 
     render(<ChatView projectId="proj-123" addToast={vi.fn()} />);
 
-    const avatar = document.querySelector(".chat-message-avatar") as HTMLElement | null;
+    const messageBubble = screen.getByTestId("chat-message-msg-001");
+    const avatar = messageBubble.querySelector(".chat-message-avatar") as HTMLElement | null;
     expect(avatar).toBeInTheDocument();
-    expect(avatar?.querySelector(".chat-model-tag")?.textContent).toContain("GPT");
+    expect(avatar?.querySelector(".chat-model-tag")).toBeNull();
   });
 
-  it("does not show duplicate model tag in message avatar for fn agent sessions", () => {
+  it("hides per-message identity entirely for fn agent (model-only) sessions even when model is set", () => {
     setupMockChat({
       activeSession: {
         id: "session-001",
@@ -1899,10 +1907,8 @@ describe("ChatView", () => {
 
     render(<ChatView projectId="proj-123" addToast={vi.fn()} />);
 
-    const avatar = document.querySelector(".chat-message-avatar") as HTMLElement | null;
+    const messageBubble = screen.getByTestId("chat-message-msg-001");
-    expect(avatar).toBeInTheDocument();
+    expect(messageBubble.querySelector(".chat-message-avatar")).toBeNull();
-    expect(within(avatar!).getByText("GPT-4o")).toBeInTheDocument();
-    expect(avatar?.querySelector(".chat-model-tag")).toBeNull();
   });
 });
 

packages/dashboard/app/hooks/chatTypes.ts

@@ -0,0 +1,40 @@
+/**
+ * Shared chat type definitions used by both `useChat` (full chat panel) and
+ * `useQuickChat` (FAB) plus the `createChatStreamHandlers` factory they
+ * compose. Keeping the types here lets the streaming-handler factory live in
+ * its own file without re-importing from one of the hooks (which would create
+ * an awkward parent→sibling dependency cycle).
+ */
+
+export interface ToolCallInfo {
+  toolName: string;
+  args?: Record<string, unknown>;
+  isError: boolean;
+  result?: unknown;
+  status: "running" | "completed";
+}
+
+export interface FallbackInfo {
+  primaryModel: string;
+  fallbackModel: string;
+  triggerPoint: "session-creation" | "prompt-time";
+}
+
+export interface ChatMessageInfo {
+  id: string;
+  sessionId: string;
+  role: "user" | "assistant" | "system";
+  content: string;
+  thinkingOutput?: string | null;
+  toolCalls?: ToolCallInfo[];
+  fallbackInfo?: FallbackInfo;
+  attachments?: Array<{
+    id: string;
+    filename: string;
+    originalName: string;
+    mimeType: string;
+    size: number;
+    createdAt: string;
+  }>;
+  createdAt: string;
+}

packages/dashboard/app/hooks/createChatStreamHandlers.ts

@@ -0,0 +1,212 @@
+import type { ChatMessage } from "@fusion/core";
+import type { Dispatch, RefObject, SetStateAction } from "react";
+import type { ChatMessageInfo, FallbackInfo, ToolCallInfo } from "./chatTypes";
+
+/**
+ * Inputs for the chat streaming-handler factory.
+ *
+ * The shared factory owns the per-stream accumulator state (text, thinking,
+ * tool calls, fallback info), the requestAnimationFrame coalescing of state
+ * updates, and the SSE event → state-setter wiring. Caller-specific behaviour
+ * for the terminal events (`onDone`, `onError`) and the optional
+ * `onFallbackSession` model-swap is provided through callbacks so that
+ * `useChat` and `useQuickChat` can plug in their own session-management
+ * semantics without re-implementing the streaming machinery.
+ */
+export interface CreateChatStreamHandlersOptions {
+  /** Active session id — used by `onFallbackSession` for parent-side updates. */
+  sessionId: string;
+  /** Optimistic temp id of the user message added before the stream started. */
+  tempUserMessageId: string;
+  /**
+   * The latest text/thinking/tool-call snapshots that are committed to React
+   * state. We pass setters (not values) so the factory can flush per-frame
+   * without rerunning the parent's effects.
+   */
+  setStreamingText: Dispatch<SetStateAction<string>>;
+  setStreamingThinking: Dispatch<SetStateAction<string>>;
+  setStreamingToolCalls: Dispatch<SetStateAction<ToolCallInfo[]>>;
+  /**
+   * Caller-side `cancelStreamingFlushes` ref slot. The factory writes its own
+   * cancel function here so `stopStreaming` (in either parent hook) can call
+   * it to abort pending RAF flushes regardless of which sendMessage owns them.
+   */
+  cancelStreamingFlushesRef: RefObject<(() => void) | null>;
+  /** Optional toast helper, used to surface fallback-model warnings + errors. */
+  addToast?: (message: string, level: "error" | "warning" | "success") => void;
+  /** Caller-supplied terminal handlers — bind in their own state setters. */
+  onDone: (data: {
+    messageId: string;
+    message?: ChatMessage;
+    accumulated: {
+      text: string;
+      thinking: string;
+      toolCalls: ToolCallInfo[];
+      fallbackInfo?: FallbackInfo;
+    };
+  }) => void;
+  onError: (data: string, tempUserMessageId: string) => void;
+  /**
+   * Fallback-model side effect for the parent (e.g. updating the session list
+   * or the active session's model fields). The factory still emits the toast.
+   */
+  onFallbackSession?: (data: FallbackInfo, sessionId: string) => void;
+}
+
+export interface ChatStreamHandlers {
+  onThinking: (delta: string) => void;
+  onText: (delta: string) => void;
+  onToolStart: (data: { toolName: string; args?: Record<string, unknown> }) => void;
+  onToolEnd: (data: { toolName: string; isError: boolean; result?: unknown }) => void;
+  onFallback: (data: FallbackInfo) => void;
+  onDone: (data: { messageId: string; message?: ChatMessage }) => void;
+  onError: (data: string) => void;
+}
+
+export interface CreateChatStreamHandlersResult {
+  handlers: ChatStreamHandlers;
+  /** Cancel any pending RAF flushes for this stream. Idempotent. */
+  cancelFlushes: () => void;
+}
+
+/**
+ * Build the SSE handler bundle that `streamChatResponse` consumes. This is the
+ * portion of the chat send/stream flow that was identical between `useChat`
+ * and `useQuickChat`; extracting it keeps both hooks in sync when we tweak
+ * coalescing, tool-call dedup, fallback toasts, etc. The terminal events
+ * (`onDone`/`onError`) and parent-side fallback bookkeeping stay caller-owned
+ * because each hook handles message persistence and error recovery
+ * differently.
+ *
+ * The factory writes its `cancelFlushes` into `cancelStreamingFlushesRef.current`
+ * so the parent's `stopStreaming` can drain pending RAF callbacks before
+ * clearing transient streaming state — preventing a flushed delta from
+ * flashing back into the UI after a stop.
+ */
+export function createChatStreamHandlers(
+  options: CreateChatStreamHandlersOptions,
+): CreateChatStreamHandlersResult {
+  const {
+    sessionId,
+    tempUserMessageId,
+    setStreamingText,
+    setStreamingThinking,
+    setStreamingToolCalls,
+    cancelStreamingFlushesRef,
+    addToast,
+    onDone,
+    onError,
+    onFallbackSession,
+  } = options;
+
+  let capturedText = "";
+  let capturedThinking = "";
+  let capturedToolCalls: ToolCallInfo[] = [];
+  let capturedFallbackInfo: FallbackInfo | undefined;
+
+  // Coalesce per-token state updates to one render per animation frame.
+  // ReactMarkdown re-parses the entire growing string on every render and
+  // every prior message also re-renders, so unthrottled setState here pegs
+  // the main thread on long replies.
+  let textRaf: number | null = null;
+  let thinkingRaf: number | null = null;
+  const flushText = (): void => {
+    textRaf = null;
+    setStreamingText(capturedText);
+  };
+  const flushThinking = (): void => {
+    thinkingRaf = null;
+    setStreamingThinking(capturedThinking);
+  };
+  const cancelFlushes = (): void => {
+    if (textRaf !== null) {
+      cancelAnimationFrame(textRaf);
+      textRaf = null;
+    }
+    if (thinkingRaf !== null) {
+      cancelAnimationFrame(thinkingRaf);
+      thinkingRaf = null;
+    }
+  };
+  cancelStreamingFlushesRef.current = cancelFlushes;
+
+  const handlers: ChatStreamHandlers = {
+    onThinking: (delta: string) => {
+      capturedThinking += delta;
+      if (thinkingRaf === null) {
+        thinkingRaf = requestAnimationFrame(flushThinking);
+      }
+    },
+    onText: (delta: string) => {
+      capturedText += delta;
+      if (textRaf === null) {
+        textRaf = requestAnimationFrame(flushText);
+      }
+    },
+    onToolStart: (data: { toolName: string; args?: Record<string, unknown> }) => {
+      capturedToolCalls = [
+        ...capturedToolCalls,
+        {
+          toolName: data.toolName,
+          args: data.args,
+          isError: false,
+          status: "running",
+        },
+      ];
+      setStreamingToolCalls(capturedToolCalls);
+    },
+    onToolEnd: (data: { toolName: string; isError: boolean; result?: unknown }) => {
+      const nextToolCalls = [...capturedToolCalls];
+      for (let i = nextToolCalls.length - 1; i >= 0; i--) {
+        const candidate = nextToolCalls[i];
+        if (candidate?.toolName === data.toolName && candidate.status === "running") {
+          nextToolCalls[i] = {
+            ...candidate,
+            status: "completed",
+            isError: data.isError,
+            result: data.result,
+          };
+          capturedToolCalls = nextToolCalls;
+          setStreamingToolCalls(nextToolCalls);
+          return;
+        }
+      }
+      capturedToolCalls = [
+        ...nextToolCalls,
+        {
+          toolName: data.toolName,
+          isError: data.isError,
+          result: data.result,
+          status: "completed",
+        },
+      ];
+      setStreamingToolCalls(capturedToolCalls);
+    },
+    onFallback: (data: FallbackInfo) => {
+      capturedFallbackInfo = data;
+      onFallbackSession?.(data, sessionId);
+      addToast?.(`Primary model unavailable. Switched to fallback ${data.fallbackModel}.`, "warning");
+    },
+    onDone: (data: { messageId: string; message?: ChatMessage }) => {
+      cancelFlushes();
+      onDone({
+        messageId: data.messageId,
+        message: data.message,
+        accumulated: {
+          text: capturedText,
+          thinking: capturedThinking,
+          toolCalls: capturedToolCalls,
+          fallbackInfo: capturedFallbackInfo,
+        },
+      });
+    },
+    onError: (data: string) => {
+      cancelFlushes();
+      onError(data, tempUserMessageId);
+    },
+  };
+
+  return { handlers, cancelFlushes };
+}
+
+export type { ChatMessageInfo };

packages/dashboard/app/hooks/useChat.ts

@@ -30,38 +30,11 @@ export interface ChatSessionInfo {
   isGenerating?: boolean;
 }
 
-export interface ToolCallInfo {
+// Re-export shared chat types so existing consumers (`import { ChatMessageInfo } from "../hooks/useChat"`)
-  toolName: string;
+// keep working — single source of truth lives in chatTypes.ts.
-  args?: Record<string, unknown>;
+export type { ChatMessageInfo, FallbackInfo, ToolCallInfo } from "./chatTypes";
-  isError: boolean;
+import type { ChatMessageInfo, FallbackInfo, ToolCallInfo } from "./chatTypes";
-  result?: unknown;
+import { createChatStreamHandlers } from "./createChatStreamHandlers";
-  status: "running" | "completed";
-}
-
-export interface FallbackInfo {
-  primaryModel: string;
-  fallbackModel: string;
-  triggerPoint: "session-creation" | "prompt-time";
-}
-
-export interface ChatMessageInfo {
-  id: string;
-  sessionId: string;
-  role: "user" | "assistant" | "system";
-  content: string;
-  thinkingOutput?: string | null;
-  toolCalls?: ToolCallInfo[];
-  fallbackInfo?: FallbackInfo;
-  attachments?: Array<{
-    id: string;
-    filename: string;
-    originalName: string;
-    mimeType: string;
-    size: number;
-    createdAt: string;
-  }>;
-  createdAt: string;
-}
 
 export interface UseChatReturn {
   // Session state
@@ -547,127 +520,37 @@ export function useChat(
       setStreamingToolCalls([]);
       setIsStreaming(true);
 
-      // Accumulate streaming text and tool calls in local variables
+      const { handlers } = createChatStreamHandlers({
-      let capturedText = "";
+        sessionId: activeSession.id,
-      let capturedThinking = "";
+        tempUserMessageId: tempId,
-      let capturedToolCalls: ToolCallInfo[] = [];
+        setStreamingText,
-      let capturedFallbackInfo: FallbackInfo | undefined;
+        setStreamingThinking,
-
+        setStreamingToolCalls,
-      // Coalesce per-token state updates to one render per animation frame.
+        cancelStreamingFlushesRef,
-      // ReactMarkdown re-parses the entire growing string on every render and
+        addToast,
-      // every prior message also re-renders, so unthrottled updates pin the
+        onFallbackSession: (data, sessionId) => {
-      // main thread for long replies.
-      let textRaf: number | null = null;
-      let thinkingRaf: number | null = null;
-      const flushText = () => {
-        textRaf = null;
-        setStreamingText(capturedText);
-      };
-      const flushThinking = () => {
-        thinkingRaf = null;
-        setStreamingThinking(capturedThinking);
-      };
-      const cancelStreamingFlushes = () => {
-        if (textRaf !== null) {
-          cancelAnimationFrame(textRaf);
-          textRaf = null;
-        }
-        if (thinkingRaf !== null) {
-          cancelAnimationFrame(thinkingRaf);
-          thinkingRaf = null;
-        }
-      };
-      cancelStreamingFlushesRef.current = cancelStreamingFlushes;
-
-      const textHandlers = {
-        onThinking: (data: string) => {
-          capturedThinking += data;
-          if (thinkingRaf === null) {
-            thinkingRaf = requestAnimationFrame(flushThinking);
-          }
-        },
-        onText: (data: string) => {
-          capturedText += data;
-          if (textRaf === null) {
-            textRaf = requestAnimationFrame(flushText);
-          }
-        },
-        onToolStart: (data: { toolName: string; args?: Record<string, unknown> }) => {
-          capturedToolCalls = [
-            ...capturedToolCalls,
-            {
-              toolName: data.toolName,
-              args: data.args,
-              isError: false,
-              status: "running",
-            },
-          ];
-          setStreamingToolCalls(capturedToolCalls);
-        },
-        onToolEnd: (data: { toolName: string; isError: boolean; result?: unknown }) => {
-          const nextToolCalls = [...capturedToolCalls];
-          for (let i = nextToolCalls.length - 1; i >= 0; i--) {
-            const candidate = nextToolCalls[i];
-            if (candidate?.toolName === data.toolName && candidate.status === "running") {
-              nextToolCalls[i] = {
-                ...candidate,
-                status: "completed",
-                isError: data.isError,
-                result: data.result,
-              };
-              capturedToolCalls = nextToolCalls;
-              setStreamingToolCalls(nextToolCalls);
-              return;
-            }
-          }
-
-          capturedToolCalls = [
-            ...nextToolCalls,
-            {
-              toolName: data.toolName,
-              isError: data.isError,
-              result: data.result,
-              status: "completed",
-            },
-          ];
-          setStreamingToolCalls(capturedToolCalls);
-        },
-        onFallback: (data: FallbackInfo) => {
-          capturedFallbackInfo = data;
           const nextModel = parseModelDescriptor(data.fallbackModel);
           setSessions((prev) => prev.map((session) =>
-            session.id === activeSession.id
+            session.id === sessionId ? { ...session, ...nextModel } : session,
-              ? {
-                  ...session,
-                  ...nextModel,
-                }
-              : session,
           ));
-          setActiveSession((prev) => prev && prev.id === activeSession.id
+          setActiveSession((prev) => prev && prev.id === sessionId ? { ...prev, ...nextModel } : prev);
-            ? {
-                ...prev,
-                ...nextModel,
-              }
-            : prev);
-          addToast?.(`Primary model unavailable. Switched to fallback ${data.fallbackModel}.`, "warning");
         },
-        onDone: (data: { messageId: string; message?: ChatMessage }) => {
+        onDone: ({ messageId, message: finalMessage, accumulated }) => {
-          cancelStreamingFlushes();
-          const finalMessage = data.message;
           const assistantMessage: ChatMessageInfo = finalMessage
             ? mapChatMessageToInfo(finalMessage)
             : {
-                id: data.messageId || `msg-${Date.now()}`,
+                id: messageId || `msg-${Date.now()}`,
                 sessionId: activeSession.id,
                 role: "assistant",
-                content: capturedText,
+                content: accumulated.text,
-                thinkingOutput: capturedThinking,
+                thinkingOutput: accumulated.thinking,
-                toolCalls: capturedToolCalls.length > 0 ? capturedToolCalls : undefined,
+                toolCalls: accumulated.toolCalls.length > 0 ? accumulated.toolCalls : undefined,
-                fallbackInfo: capturedFallbackInfo,
+                fallbackInfo: accumulated.fallbackInfo,
                 createdAt: new Date().toISOString(),
               };
 
-          // Track this message ID so SSE handler skips it if event arrives first
+          // Track this message ID so the SSE chatMessageAdded handler skips it
+          // if the broadcast event arrives before our optimistic add settles.
           streamingMessageIdsRef.current.add(assistantMessage.id);
 
           // Preserve user message and add assistant message
@@ -693,9 +576,8 @@ export function useChat(
             sendMessage(queuedMessage);
           }
         },
-        onError: (data: string) => {
+        onError: (data, tempUserMessageId) => {
-          cancelStreamingFlushes();
+          setMessages((prev) => prev.filter((m) => m.id !== tempUserMessageId));
-          setMessages((prev) => prev.filter((m) => m.id !== tempId));
           setStreamingText("");
           setStreamingThinking("");
           setStreamingToolCalls([]);
@@ -713,9 +595,9 @@ export function useChat(
             }
           }
         },
-      };
+      });
 
-      streamRef.current = streamChatResponse(activeSession.id, content, textHandlers, attachments, projectId);
+      streamRef.current = streamChatResponse(activeSession.id, content, handlers, attachments, projectId);
     },
     [activeSession, isStreaming, projectId, refreshSessions, addToast],
   );

packages/dashboard/app/hooks/useQuickChat.ts

@@ -12,30 +12,14 @@ import {
 
 export const FN_AGENT_ID = "__fn_agent__";
 
-export interface ToolCallInfo {
+// Re-export shared chat types so existing consumers keep working — single
-  toolName: string;
+// source of truth lives in chatTypes.ts and is shared with useChat.
-  args?: Record<string, unknown>;
+// Note: useQuickChat's previous local `ChatMessageInfo` lacked the
-  isError: boolean;
+// `attachments` field; the shared type adds it (a strict superset), which is
-  result?: unknown;
+// safe for callers that ignore it.
-  status: "running" | "completed";
+export type { ChatMessageInfo, FallbackInfo, ToolCallInfo } from "./chatTypes";
-}
+import type { ChatMessageInfo, FallbackInfo, ToolCallInfo } from "./chatTypes";
-
+import { createChatStreamHandlers } from "./createChatStreamHandlers";
-export interface FallbackInfo {
-  primaryModel: string;
-  fallbackModel: string;
-  triggerPoint: "session-creation" | "prompt-time";
-}
-
-export interface ChatMessageInfo {
-  id: string;
-  sessionId: string;
-  role: "user" | "assistant" | "system";
-  content: string;
-  thinkingOutput?: string | null;
-  toolCalls?: ToolCallInfo[];
-  fallbackInfo?: FallbackInfo;
-  createdAt: string;
-}
 
 interface ModelSelection {
   modelProvider?: string;
@@ -559,121 +543,32 @@ export function useQuickChat(
         setStreamingToolCalls([]);
         setIsStreaming(true);
 
-        // Accumulate streaming text and tool calls in local variables
+        const { handlers } = createChatStreamHandlers({
-        let capturedText = "";
+          sessionId: activeSession.id,
-        let capturedThinking = "";
+          tempUserMessageId: tempId,
-        let capturedToolCalls: ToolCallInfo[] = [];
+          setStreamingText,
-        let capturedFallbackInfo: FallbackInfo | undefined;
+          setStreamingThinking,
-
+          setStreamingToolCalls,
-        // Coalesce per-token state updates to one render per animation frame —
+          cancelStreamingFlushesRef,
-        // unthrottled setStreamingText pegs the main thread on long replies.
+          addToast,
-        let textRaf: number | null = null;
+          onFallbackSession: (data, sessionId) => {
-        let thinkingRaf: number | null = null;
-        const flushText = () => {
-          textRaf = null;
-          setStreamingText(capturedText);
-        };
-        const flushThinking = () => {
-          thinkingRaf = null;
-          setStreamingThinking(capturedThinking);
-        };
-        const cancelStreamingFlushes = () => {
-          if (textRaf !== null) {
-            cancelAnimationFrame(textRaf);
-            textRaf = null;
-          }
-          if (thinkingRaf !== null) {
-            cancelAnimationFrame(thinkingRaf);
-            thinkingRaf = null;
-          }
-        };
-        cancelStreamingFlushesRef.current = cancelStreamingFlushes;
-
-        const textHandlers = {
-          onThinking: (data: string) => {
-            capturedThinking += data;
-            if (thinkingRaf === null) {
-              thinkingRaf = requestAnimationFrame(flushThinking);
-            }
-          },
-          onText: (data: string) => {
-            capturedText += data;
-            if (textRaf === null) {
-              textRaf = requestAnimationFrame(flushText);
-            }
-          },
-          onToolStart: (data: { toolName: string; args?: Record<string, unknown> }) => {
-            capturedToolCalls = [
-              ...capturedToolCalls,
-              {
-                toolName: data.toolName,
-                args: data.args,
-                isError: false,
-                status: "running",
-              },
-            ];
-            setStreamingToolCalls(capturedToolCalls);
-          },
-          onToolEnd: (data: { toolName: string; isError: boolean; result?: unknown }) => {
-            const nextToolCalls = [...capturedToolCalls];
-            for (let i = nextToolCalls.length - 1; i >= 0; i--) {
-              const candidate = nextToolCalls[i];
-              if (candidate?.toolName === data.toolName && candidate.status === "running") {
-                nextToolCalls[i] = {
-                  ...candidate,
-                  status: "completed",
-                  isError: data.isError,
-                  result: data.result,
-                };
-                capturedToolCalls = nextToolCalls;
-                setStreamingToolCalls(nextToolCalls);
-                return;
-              }
-            }
-
-            capturedToolCalls = [
-              ...nextToolCalls,
-              {
-                toolName: data.toolName,
-                isError: data.isError,
-                result: data.result,
-                status: "completed",
-              },
-            ];
-            setStreamingToolCalls(capturedToolCalls);
-          },
-          onFallback: (data: FallbackInfo) => {
-            capturedFallbackInfo = data;
             const nextModel = parseModelDescriptor(data.fallbackModel);
             setSessions((prev) => prev.map((session) =>
-              session.id === activeSession.id
+              session.id === sessionId ? { ...session, ...nextModel } : session,
-                ? {
-                    ...session,
-                    ...nextModel,
-                  }
-                : session,
             ));
-            setActiveSession((prev) => prev && prev.id === activeSession.id
+            setActiveSession((prev) => prev && prev.id === sessionId ? { ...prev, ...nextModel } : prev);
-              ? {
-                  ...prev,
-                  ...nextModel,
-                }
-              : prev);
-            addToast?.(`Primary model unavailable. Switched to fallback ${data.fallbackModel}.`, "warning");
           },
-          onDone: (data: { messageId: string; message?: ChatMessage }) => {
+          onDone: ({ messageId, message: finalMessage, accumulated }) => {
-            cancelStreamingFlushes();
-            const finalMessage = data.message;
             const assistantMessage: ChatMessageInfo = finalMessage
               ? mapChatMessageToInfo(finalMessage)
               : {
-                  id: data.messageId || `msg-${Date.now()}`,
+                  id: messageId || `msg-${Date.now()}`,
                   sessionId: activeSession.id,
                   role: "assistant",
-                  content: capturedText,
+                  content: accumulated.text,
-                  thinkingOutput: capturedThinking || undefined,
+                  thinkingOutput: accumulated.thinking || undefined,
-                  toolCalls: capturedToolCalls.length > 0 ? capturedToolCalls : undefined,
+                  toolCalls: accumulated.toolCalls.length > 0 ? accumulated.toolCalls : undefined,
-                  fallbackInfo: capturedFallbackInfo,
+                  fallbackInfo: accumulated.fallbackInfo,
                   createdAt: new Date().toISOString(),
                 };
 
@@ -695,8 +590,7 @@ export function useQuickChat(
               void sendMessage(queuedMessage);
             }
           },
-          onError: (data: string) => {
+          onError: (data) => {
-            cancelStreamingFlushes();
             setStreamingText("");
             setStreamingThinking("");
             setStreamingToolCalls([]);
@@ -718,9 +612,9 @@ export function useQuickChat(
 
             void reloadMessages();
           },
-        };
+        });
 
-        streamRef.current = streamChatResponse(activeSession.id, content, textHandlers, attachments, projectId);
+        streamRef.current = streamChatResponse(activeSession.id, content, handlers, attachments, projectId);
       });
 
       // Preserve rejection semantics for awaiters while preventing unhandled rejection noise

packages/dashboard/src/chat.ts

@@ -1013,17 +1013,21 @@ export class ChatManager {
         },
       };
 
+      // Single agent-creation path for both regular chat and QuickChat. When
+      // the chat is bound to an agent that declares a runtime hint we pass it
+      // through; when there's no agent (e.g. QuickChat's model-only mode) or
+      // no hint, `createResolvedAgentSession` falls back to the default
+      // runtime via `resolveRuntime`. This avoids the previous divergence
+      // where QuickChat went through `createFnAgent` and hit pi-ai's shared
+      // `cleanupSessionResources(sessionId)` tear-down across overlapping
+      // sessions opened from the same CLI session file.
       const agentRuntimeHint = agent ? extractRuntimeHint(agent.runtimeConfig) : undefined;
-      if (agentRuntimeHint) {
       agentResult = await createResolvedAgentSession({
         sessionPurpose: "executor",
-          runtimeHint: agentRuntimeHint,
+        ...(agentRuntimeHint ? { runtimeHint: agentRuntimeHint } : {}),
         pluginRunner: this.pluginRunner,
         ...sessionOptions,
       });
-      } else {
-        agentResult = await createFnAgent(sessionOptions);
-      }
       this.activeGenerations.set(sessionId, { abortController, agentResult, generationId });
 
       if (abortController.signal.aborted) {
@@ -1143,16 +1147,29 @@ export class ChatManager {
         data: errorMessage,
       }, broadcastOptions);
     } finally {
-      // Only clear the active-generation slot if it still belongs to us. If a newer
+      // Only clear the active-generation slot if it still belongs to us. If a
-      // sendMessage pre-empted us via beginGeneration, the slot now holds that newer
+      // newer sendMessage pre-empted us via beginGeneration, the slot now holds
-      // generation's controller and must not be deleted by our cleanup.
+      // that newer generation's controller and must not be deleted by us.
       const current = this.activeGenerations.get(sessionId);
-      if (current?.generationId === generationId) {
+      const stillOwnsSlot = current?.generationId === generationId;
+      if (stillOwnsSlot) {
         this.activeGenerations.delete(sessionId);
       }
 
-      // Always dispose agent session
+      // Dispose the agent session — but ONLY when we still own the slot.
-      if (agentResult) {
+      //
+      // pi-ai's `cleanupSessionResources(sessionId)` fires globally-registered
+      // cleanup callbacks keyed by sessionId, and two agents opened from the
+      // same CLI session file share that sessionId. If a newer generation has
+      // taken over for the same chat session, disposing this (older) agent
+      // tears down resources the newer agent is actively using — the model
+      // produces no output and the next turn looks like a silent failure.
+      //
+      // The newer generation will dispose its own agent in its own finally.
+      // The older agent's resources are largely garbage-collectible without
+      // an explicit dispose; the small leak per pre-empted generation is
+      // worth avoiding the cross-generation tear-down.
+      if (stillOwnsSlot && agentResult) {
         try {
           agentResult.session.dispose?.();
         } catch (err) {
@@ -1209,6 +1226,12 @@ export class ChatManager {
  */
 export function __setCreateFnAgent(mock: typeof createFnAgent): void {
   createFnAgent = mock;
+  // chat.ts now routes both regular chat and QuickChat through
+  // `createResolvedAgentSession`, which would normally bypass this mock and
+  // hit the real engine. Mirror the same fake into the resolved-session slot
+  // so existing test setups that only call `__setCreateFnAgent` continue to
+  // work.
+  createResolvedAgentSession = (async (options: any) => mock(options)) as typeof createResolvedAgentSession;
 }
 
 /**