🤖 refactor: use message queue for compact continue messages (#650)

## Stack
1. #685 
1. #683 
1. #670
1. #650 ⬅ This PR (base)

## Problem

Compact continue messages were handled by a frontend hook that watched
workspace states and manually sent continue messages after compaction.
This was complex, had potential race conditions, and poor separation of
concerns.

Relates to #651.

## Solution

Use the existing message queue system:
- Backend queues continue message when compaction starts
- Queue auto-sends when stream ends (existing behavior)
- Clear queue on error paths

**Benefits:** Simpler (-134 lines), more reliable, better UX (continue
message visible in queue).

_Generated with `mux`_

Author: ethanndickson

src/browser/App.tsx

@@ -12,7 +12,6 @@ import { usePersistedState, updatePersistedState } from "./hooks/usePersistedSta
 import { matchesKeybind, KEYBINDS } from "./utils/ui/keybinds";
 import { useResumeManager } from "./hooks/useResumeManager";
 import { useUnreadTracking } from "./hooks/useUnreadTracking";
-import { useAutoCompactContinue } from "./hooks/useAutoCompactContinue";
 import { useWorkspaceStoreRaw, useWorkspaceRecency } from "./stores/WorkspaceStore";
 import { ChatInput } from "./components/ChatInput/index";
 import type { ChatInputAPI } from "./components/ChatInput/types";
@@ -117,9 +116,6 @@ function AppInner() {
   // Auto-resume interrupted streams on app startup and when failures occur
   useResumeManager();
 
-  // Handle auto-continue after compaction (when user uses /compact -c)
-  useAutoCompactContinue();
-
   // Sync selectedWorkspace with URL hash
   useEffect(() => {
     if (selectedWorkspace) {

src/browser/api.ts

@@ -263,7 +263,7 @@ const webApi: IPCApi = {
       invokeIPC(IPC_CHANNELS.WORKSPACE_RESUME_STREAM, workspaceId, options),
     interruptStream: (workspaceId, options) =>
       invokeIPC(IPC_CHANNELS.WORKSPACE_INTERRUPT_STREAM, workspaceId, options),
-    clearQueue: (workspaceId) => invokeIPC(IPC_CHANNELS.WORKSPACE_QUEUE_CLEAR, workspaceId),
+    clearQueue: (workspaceId) => invokeIPC(IPC_CHANNELS.WORKSPACE_CLEAR_QUEUE, workspaceId),
     truncateHistory: (workspaceId, percentage) =>
       invokeIPC(IPC_CHANNELS.WORKSPACE_TRUNCATE_HISTORY, workspaceId, percentage),
     replaceChatHistory: (workspaceId, summaryMessage) =>

src/browser/hooks/useAutoCompactContinue.ts

@@ -672,12 +672,6 @@ export class WorkspaceStore {
     const historicalUsage =
       currentUsage.usageHistory.length > 0 ? sumUsageHistory(currentUsage.usageHistory) : undefined;
 
-    // Extract continueMessage from compaction-request before history gets replaced
-    const compactRequestMsg = findCompactionRequestMessage(aggregator);
-    const muxMeta = compactRequestMsg?.metadata?.muxMetadata;
-    const continueMessage =
-      muxMeta?.type === "compaction-request" ? muxMeta.parsed.continueMessage : undefined;
-
     const summaryMessage = createMuxMessage(
       `summary-${Date.now()}-${Math.random().toString(36).substring(2, 11)}`,
       "assistant",
@@ -697,10 +691,7 @@ export class WorkspaceStore {
           metadata && "systemMessageTokens" in metadata
             ? (metadata.systemMessageTokens as number | undefined)
             : undefined,
-        // Store continueMessage in summary so it survives history replacement
-        muxMetadata: continueMessage
-          ? { type: "compaction-result", continueMessage, requestId: compactRequestMsg?.id }
-          : { type: "normal" },
+        muxMetadata: { type: "normal" },
       }
     );
 

src/browser/stores/WorkspaceStore.ts

@@ -27,7 +27,7 @@ export const IPC_CHANNELS = {
   WORKSPACE_SEND_MESSAGE: "workspace:sendMessage",
   WORKSPACE_RESUME_STREAM: "workspace:resumeStream",
   WORKSPACE_INTERRUPT_STREAM: "workspace:interruptStream",
-  WORKSPACE_QUEUE_CLEAR: "workspace:queue:clear",
+  WORKSPACE_CLEAR_QUEUE: "workspace:clearQueue",
   WORKSPACE_TRUNCATE_HISTORY: "workspace:truncateHistory",
   WORKSPACE_REPLACE_HISTORY: "workspace:replaceHistory",
   WORKSPACE_STREAM_HISTORY: "workspace:streamHistory",

src/common/constants/ipc-constants.ts

@@ -120,15 +120,6 @@ export const PREFERRED_COMPACTION_MODEL_KEY = "preferredCompactionModel";
  */
 export const VIM_ENABLED_KEY = "vimEnabled";
 
-/**
- * Get the localStorage key for the compact continue message for a workspace
- * Temporarily stores the continuation prompt for the current compaction
- * Should be deleted immediately after use to prevent bugs
- */
-export function getCompactContinueMessageKey(workspaceId: string): string {
-  return `compactContinueMessage:${workspaceId}`;
-}
-
 /**
  * Get the localStorage key for hunk expand/collapse state in Review tab
  * Stores user's manual expand/collapse preferences per hunk
@@ -158,7 +149,6 @@ export function getReviewSearchStateKey(workspaceId: string): string {
 
 /**
  * List of workspace-scoped key functions that should be copied on fork and deleted on removal
- * Note: Excludes ephemeral keys like getCompactContinueMessageKey
  */
 const PERSISTENT_WORKSPACE_KEY_FUNCTIONS: Array<(workspaceId: string) => string> = [
   getModelKey,
@@ -177,7 +167,6 @@ const PERSISTENT_WORKSPACE_KEY_FUNCTIONS: Array<(workspaceId: string) => string>
  */
 const EPHEMERAL_WORKSPACE_KEY_FUNCTIONS: Array<(workspaceId: string) => string> = [
   getCancelledCompactionKey,
-  getCompactContinueMessageKey,
 ];
 
 /**

src/common/constants/storage.ts

@@ -20,11 +20,6 @@ export type MuxFrontendMetadata =
       rawCommand: string; // The original /compact command as typed by user (for display)
       parsed: CompactionRequestData;
     }
-  | {
-      type: "compaction-result";
-      continueMessage: string; // Message to send after compaction completes
-      requestId?: string; // ID of the compaction-request user message that produced this summary (for idempotency)
-    }
   | {
       type: "normal"; // Regular messages
     };

src/common/types/message.ts

@@ -82,7 +82,7 @@ const api: IPCApi = {
     interruptStream: (workspaceId: string, options?: { abandonPartial?: boolean }) =>
       ipcRenderer.invoke(IPC_CHANNELS.WORKSPACE_INTERRUPT_STREAM, workspaceId, options),
     clearQueue: (workspaceId: string) =>
-      ipcRenderer.invoke(IPC_CHANNELS.WORKSPACE_QUEUE_CLEAR, workspaceId),
+      ipcRenderer.invoke(IPC_CHANNELS.WORKSPACE_CLEAR_QUEUE, workspaceId),
     truncateHistory: (workspaceId, percentage) =>
       ipcRenderer.invoke(IPC_CHANNELS.WORKSPACE_TRUNCATE_HISTORY, workspaceId, percentage),
     replaceChatHistory: (workspaceId, summaryMessage) =>

src/desktop/preload.ts

@@ -314,6 +314,15 @@ export class AgentSession {
 
     this.emitChatEvent(userMessage);
 
+    // If this is a compaction request with a continue message, queue it for auto-send after compaction
+    const muxMeta = options?.muxMetadata;
+    if (muxMeta?.type === "compaction-request" && muxMeta.parsed.continueMessage && options) {
+      // Strip out edit-specific and compaction-specific fields so the queued message is a fresh user message
+      const { muxMetadata, mode, editMessageId, ...continueOptions } = options;
+      this.messageQueue.add(muxMeta.parsed.continueMessage, continueOptions);
+      this.emitQueuedMessageChanged();
+    }
+
     if (!options?.model || options.model.trim().length === 0) {
       return Err(
         createUnknownSendMessageError("No model specified. Please select a model using /model.")

src/node/services/agentSession.ts

@@ -1119,7 +1119,7 @@ export class IpcMain {
       }
     );
 
-    ipcMain.handle(IPC_CHANNELS.WORKSPACE_QUEUE_CLEAR, (_event, workspaceId: string) => {
+    ipcMain.handle(IPC_CHANNELS.WORKSPACE_CLEAR_QUEUE, (_event, workspaceId: string) => {
       try {
         const session = this.getOrCreateSession(workspaceId);
         session.clearQueue();