fix(desktop): tolerate unparsed display_metadata from an older backend

The desktop and the Hermes backend it talks to version independently — a
remote VM running an older build still serves display_metadata as JSON text.
Indexing into that string with `in` threw and failed the whole resume, so
narrow the type to admit a string and parse it before reading task_count.
Falling back to the generic label keeps a delegation event renderable even
when the metadata is unusable.

Co-authored-by: xxxigm <xxxigm@users.noreply.github.com>
Co-authored-by: Studio729 <Studio729@users.noreply.github.com>

apps/desktop/src/lib/chat-messages.test.ts

@@ -1,5 +1,7 @@
 import { describe, expect, it } from 'vitest'
 
+import type { SessionMessage } from '@/types/hermes'
+
 import type { ChatMessage, ChatMessagePart } from './chat-messages'
 import {
   appendAssistantTextPart,
@@ -191,6 +193,30 @@ describe('toChatMessages', () => {
       'background agent work finished'
     ])
   })
+
+  // A backend older than this app serves display_metadata as unparsed JSON
+  // text. Indexing into that string used to throw and fail the whole resume.
+  it.each([
+    ['an object', { delegation_id: 'deleg_1', task_count: 2 }, '2 background agents finished'],
+    ['JSON text', JSON.stringify({ delegation_id: 'deleg_1', task_count: 1 }), '1 background agent finished'],
+    ['unparseable text', '{not-json', 'background agent work finished'],
+    ['text that is not an object', '"deleg_1"', 'background agent work finished'],
+    ['a missing task count', { delegation_id: 'deleg_1' }, 'background agent work finished']
+  ])('labels a delegation event given %s', (_case, displayMetadata, expected) => {
+    const read = () =>
+      toChatMessages([
+        {
+          role: 'user',
+          content: 'opaque delegation context payload',
+          display_kind: 'async_delegation_complete',
+          display_metadata: displayMetadata as SessionMessage['display_metadata'],
+          timestamp: 1
+        }
+      ])
+
+    expect(read).not.toThrow()
+    expect(chatMessageText(read()[0])).toBe(expected)
+  })
 })
 
 describe('renderMediaTags', () => {

apps/desktop/src/lib/chat-messages.ts

@@ -311,16 +311,35 @@ function transcriptContent(displayKind: SessionMessage['display_kind'], content:
   return displayKind === 'hidden' ? null : content
 }
 
+// A remote backend older than this app serves display_metadata as raw JSON text,
+// and `in` throws on a primitive — which used to fail the whole session resume.
+function timelineTaskCount(metadata: SessionMessage['display_metadata']): number | undefined {
+  let parsed: unknown = metadata
+
+  if (typeof parsed === 'string') {
+    try {
+      parsed = JSON.parse(parsed)
+    } catch {
+      return undefined
+    }
+  }
+
+  if (!parsed || typeof parsed !== 'object') {
+    return undefined
+  }
+
+  const count = (parsed as { task_count?: unknown }).task_count
+
+  return typeof count === 'number' ? count : undefined
+}
+
 function timelineDisplayContent(message: SessionMessage, content: string): string {
   if (message.display_kind === 'model_switch') {
     return 'model changed'
   }
 
   if (message.display_kind === 'async_delegation_complete') {
-    const count =
-      message.display_metadata && 'task_count' in message.display_metadata
-        ? message.display_metadata.task_count
-        : undefined
+    const count = timelineTaskCount(message.display_metadata)
 
     return count === undefined
       ? 'background agent work finished'

apps/desktop/src/types/hermes.ts

@@ -494,7 +494,11 @@ export interface SessionMessage {
   reasoning_content?: null | string
   reasoning_details?: unknown
   display_kind?: 'async_delegation_complete' | 'hidden' | 'model_switch' | string
-  display_metadata?: TimelineDisplayMetadata
+  /**
+   * A backend older than this app can still serve this as unparsed JSON text,
+   * so readers must narrow before indexing into it.
+   */
+  display_metadata?: string | TimelineDisplayMetadata
   role: 'assistant' | 'system' | 'tool' | 'user'
   text?: unknown
   timestamp?: number