feat(desktop): add chat abort support with partial content preservation

Add stop button to interrupt agent generation mid-stream. The send button
toggles to a stop icon during loading. Abort propagates from UI through
IPC to the Agent layer (PiAgentCore.abort()), preserving all partial
content in the agent's context so users can follow up immediately.

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

apps/desktop/src/main/electron-env.d.ts

@@ -222,6 +222,7 @@ interface ElectronAPI {
     unsubscribe: (agentId: string) => Promise<{ ok: boolean }>
     getHistory: (agentId: string, options?: { offset?: number; limit?: number }) => Promise<{ messages: unknown[]; total: number; offset: number; limit: number }>
     send: (agentId: string, content: string) => Promise<{ ok?: boolean; error?: string }>
+    abort: (agentId: string) => Promise<{ ok?: boolean; error?: string }>
     resolveExecApproval: (approvalId: string, decision: string) => Promise<{ ok: boolean }>
     onEvent: (callback: (event: LocalChatEvent) => void) => void
     offEvent: () => void

apps/desktop/src/main/ipc/hub.ts

@@ -394,6 +394,20 @@ export function registerHubIpcHandlers(): void {
     return { ok: true }
   })
 
+  /**
+   * Abort the current agent run for local chat.
+   */
+  ipcMain.handle('localChat:abort', async (_event, agentId: string) => {
+    const h = getHub()
+    const agent = h.getAgent(agentId)
+    if (!agent) {
+      return { error: `Agent not found: ${agentId}` }
+    }
+    agent.abort()
+    safeLog(`[IPC] Abort sent to agent: ${agentId}`)
+    return { ok: true }
+  })
+
   /**
    * Resolve an exec approval request for local chat.
    */

apps/desktop/src/preload/index.ts

@@ -268,6 +268,8 @@ const electronAPI = {
       ipcRenderer.invoke('localChat:getHistory', agentId, options),
     /** Send message to agent via direct IPC (no Gateway) */
     send: (agentId: string, content: string) => ipcRenderer.invoke('localChat:send', agentId, content),
+    /** Abort the current agent run */
+    abort: (agentId: string) => ipcRenderer.invoke('localChat:abort', agentId),
     /** Resolve an exec approval request */
     resolveExecApproval: (approvalId: string, decision: string) =>
       ipcRenderer.invoke('localChat:resolveExecApproval', approvalId, decision),

apps/desktop/src/renderer/src/components/local-chat.tsx

@@ -19,6 +19,7 @@ export function LocalChat() {
     error,
     pendingApprovals,
     sendMessage,
+    abortGeneration,
     loadMore,
     resolveApproval,
     clearError,
@@ -90,6 +91,7 @@ export function LocalChat() {
         error={error}
         pendingApprovals={pendingApprovals}
         sendMessage={sendMessage}
+        onAbort={abortGeneration}
         loadMore={loadMore}
         resolveApproval={resolveApproval}
         errorAction={errorAction}

apps/desktop/src/renderer/src/hooks/use-local-chat.ts

@@ -109,6 +109,12 @@ export function useLocalChat() {
     [agentId],
   )
 
+  const abortGeneration = useCallback(() => {
+    if (!agentId) return
+    window.electronAPI.localChat.abort(agentId).catch(() => {})
+    setIsLoading(false)
+  }, [agentId])
+
   const loadMore = useCallback(async () => {
     const currentOffset = offsetRef.current
     if (!agentId || currentOffset == null || currentOffset <= 0 || isLoadingMoreRef.current) return
@@ -158,6 +164,7 @@ export function useLocalChat() {
     error: chat.error,
     pendingApprovals: chat.pendingApprovals,
     sendMessage,
+    abortGeneration,
     loadMore,
     resolveApproval,
     clearError,

packages/core/src/agent/async-agent.ts

@@ -242,6 +242,15 @@ export class AsyncAgent {
     return this.agent.hasQueuedMessages();
   }
 
+  /**
+   * Abort the currently running prompt.
+   * Bypasses the serial queue — directly interrupts the running PiAgentCore prompt.
+   * Partial content is preserved in agent context. Safe to call when idle (no-op).
+   */
+  abort(): void {
+    this.agent.abort();
+  }
+
   private shouldForwardEvent(event: AgentEvent | MulticaEvent): boolean {
     if (!this.agent.isInternalRun) return true;
     if (!this.forwardInternalAssistant) return false;

packages/core/src/agent/runner.ts

@@ -92,6 +92,7 @@ export class Agent {
   // Internal run state
   private _internalRun = false;
   private _isRunning = false;
+  private _aborted = false;
   private _runMutex: Promise<void> = Promise.resolve();
   private currentUserDisplayPrompt: string | undefined;
 
@@ -429,6 +430,7 @@ export class Agent {
     this.output.state.lastAssistantText = "";
     this.currentUserDisplayPrompt = options?.displayPrompt;
     this._isRunning = true;
+    this._aborted = false;
 
     try {
       // Early validation: check API key before calling PiAgentCore.prompt(),
@@ -489,9 +491,27 @@ export class Agent {
       const thinking = this.reasoningMode !== "off"
         ? this.output.state.lastAssistantThinking || undefined
         : undefined;
+
+      // On abort: clear the error so it doesn't propagate as an agent error,
+      // and return partial text without an error flag.
+      if (this._aborted) {
+        this.agent.state.error = undefined;
+        return { text: this.output.state.lastAssistantText, thinking, error: undefined };
+      }
+
       return { text: this.output.state.lastAssistantText, thinking, error: this.agent.state.error };
     } finally {
+      // On abort, persist any partial messages that pi-agent-core appended
+      // via appendMessage() (no message_end event fires for those).
+      if (this._aborted) {
+        const messages = this.agent.state.messages;
+        const lastMsg = messages[messages.length - 1];
+        if (lastMsg?.role === "assistant") {
+          this.session.saveMessage(lastMsg);
+        }
+      }
       this._isRunning = false;
+      this._aborted = false;
       this.currentUserDisplayPrompt = undefined;
     }
   }
@@ -701,6 +721,17 @@ export class Agent {
     return this.agent.hasQueuedMessages();
   }
 
+  /**
+   * Abort the currently running prompt.
+   * Triggers PiAgentCore's internal AbortController. The running prompt()
+   * will resolve (not throw), partial content stays in state.messages.
+   * Safe to call when no run is active (no-op).
+   */
+  abort(): void {
+    this._aborted = true;
+    this.agent.abort();
+  }
+
   /**
    * Persist a synthetic assistant message into both in-memory state and session JSONL.
    * Used after an internal run to keep the LLM summary visible in future turns

packages/ui/src/components/chat-input.tsx

@@ -4,7 +4,7 @@ import { useEditor, EditorContent } from "@tiptap/react";
 import StarterKit from "@tiptap/starter-kit";
 import Placeholder from "@tiptap/extension-placeholder";
 import { Button } from "@multica/ui/components/ui/button";
-import { ArrowUp02Icon } from "@hugeicons/core-free-icons";
+import { ArrowUp02Icon, StopIcon } from "@hugeicons/core-free-icons";
 import { HugeiconsIcon } from "@hugeicons/react";
 import { cn } from "@multica/ui/lib/utils";
 import "./chat-input.css";
@@ -18,12 +18,14 @@ export interface ChatInputRef {
 
 interface ChatInputProps {
   onSubmit?: (value: string) => void;
+  onAbort?: () => void;
+  isLoading?: boolean;
   disabled?: boolean;
   placeholder?: string;
 }
 
 export const ChatInput = forwardRef<ChatInputRef, ChatInputProps>(
-  function ChatInput({ onSubmit, disabled, placeholder = "Type a message..." }, ref) {
+  function ChatInput({ onSubmit, onAbort, isLoading, disabled, placeholder = "Type a message..." }, ref) {
     // Use ref to avoid stale closure in Tiptap keydown handler
     const onSubmitRef = useRef(onSubmit);
     onSubmitRef.current = onSubmit;
@@ -109,6 +111,16 @@ export const ChatInput = forwardRef<ChatInputRef, ChatInputProps>(
       editor.commands.clearContent();
     };
 
+    const handleButtonClick = () => {
+      if (isLoading && onAbort) {
+        onAbort();
+      } else {
+        handleSubmit();
+      }
+    };
+
+    const showStop = isLoading && !!onAbort;
+
     return (
       <div className={cn(
         "chat-input-editor bg-card rounded-xl p-2 border border-border transition-colors",
@@ -116,8 +128,8 @@ export const ChatInput = forwardRef<ChatInputRef, ChatInputProps>(
       )}>
         <EditorContent className="min-h-12" editor={editor} />
         <div className="flex items-center justify-end pt-2">
-          <Button size="icon" onClick={handleSubmit} disabled={disabled}>
-            <HugeiconsIcon strokeWidth={2.5} icon={ArrowUp02Icon} />
+          <Button size="icon" onClick={handleButtonClick} disabled={disabled && !showStop}>
+            <HugeiconsIcon strokeWidth={2.5} icon={showStop ? StopIcon : ArrowUp02Icon} />
           </Button>
         </div>
       </div>

packages/ui/src/components/chat-view.tsx

@@ -36,6 +36,7 @@ export interface ChatViewProps {
   error: ChatViewError | null;
   pendingApprovals: ChatViewApproval[];
   sendMessage: (text: string) => void;
+  onAbort?: () => void;
   loadMore?: () => void;
   resolveApproval: (approvalId: string, decision: "allow-once" | "allow-always" | "deny") => void;
   onDisconnect?: () => void;
@@ -53,6 +54,7 @@ export function ChatView({
   error,
   pendingApprovals,
   sendMessage,
+  onAbort,
   loadMore,
   resolveApproval,
   onDisconnect,
@@ -257,7 +259,9 @@ export function ChatView({
       <footer className="container px-4 pb-3 pt-1">
         <ChatInput
           onSubmit={sendMessage}
-          disabled={isLoading || (!!error && error.code !== 'AGENT_ERROR')}
+          onAbort={onAbort}
+          isLoading={isLoading}
+          disabled={!!error && error.code !== 'AGENT_ERROR'}
           placeholder={error && error.code !== 'AGENT_ERROR' ? "Connection error" : "Ask your Agent..."}
         />
       </footer>