fix: stabilize ai design history switching

electron/api/routes/image-workspace.ts

@@ -18,7 +18,10 @@ import {
   type DesignRenameWorkspaceInput,
   type DesignSubmitMessageInput,
 } from '../../../shared/image-workspace';
-import { DesignWorkspaceModuleError } from '../../image-workspace/module';
+import {
+  DesignWorkspaceModuleError,
+  type DesignWorkspaceEventSubscription,
+} from '../../image-workspace/module';
 import type { HostApiContext } from '../context';
 import {
   flushStreamingHeaders,
@@ -328,19 +331,25 @@ async function relayWorkspaceEvents(
   }
   const header = req.headers['last-event-id'];
   const afterEventId = Array.isArray(header) ? header[0] : header;
-  const subscription = await ctx.imageWorkspace.openWorkspaceEvents({
-    workspaceId,
-    conversationId,
-    ...(afterEventId ? { afterEventId } : {}),
-  });
+  let subscription: DesignWorkspaceEventSubscription | null = null;
   let closed = false;
   const close = () => {
     if (closed) return;
     closed = true;
-    subscription.close();
+    subscription?.close();
   };
   res.once('close', close);
   try {
+    const opened = await ctx.imageWorkspace.openWorkspaceEvents({
+      workspaceId,
+      conversationId,
+      ...(afterEventId ? { afterEventId } : {}),
+    });
+    if (closed) {
+      opened.close();
+      return;
+    }
+    subscription = opened;
     res.statusCode = 200;
     res.setHeader('Content-Type', 'text/event-stream; charset=utf-8');
     res.setHeader('Cache-Control', 'no-cache, no-transform');
@@ -456,7 +465,13 @@ export async function handleImageWorkspaceRoutes(
       && segments[0] === 'workspaces'
       && segments[2] === 'conversations'
       && req.method === 'GET') {
-      sendData(res, await ctx.imageWorkspace.getConversation(segments[1], segments[3]));
+      const before = url.searchParams.get('before');
+      sendData(
+        res,
+        before === null
+          ? await ctx.imageWorkspace.getConversation(segments[1], segments[3])
+          : await ctx.imageWorkspace.getConversation(segments[1], segments[3], before),
+      );
       return true;
     }