fix(mobile): show a message the host recorded and then rejected in place, as on the desktop

Design case 1: the phone no longer hands such a message back or banners it
(this branch's earlier change), so its row is where it lives; the phone now
draws it as not sent, like the desktop, and leaves one a queued card holds to
that card.

mobile/src/session/use-mobile-structured-agent-session-send.test.tsx

@@ -5,6 +5,7 @@ import type { AgentJournalDispatchState } from '../../../src/shared/agent-sessio
 import type { AgentSessionSubscribeEvent } from '../../../src/shared/agent-session-wire'
 import type { RpcClient } from '../transport/rpc-client'
 import { markRpcDeliveryUnknown } from '../transport/rpc-delivery-ambiguity'
+import { agentJournalSubmissionKey } from '../../../src/shared/agent-session-journal-item-key'
 import { resetMobileStructuredSendOperationJournalForTests } from './mobile-structured-send-operation-journal'
 import { structuredSendResultFixture } from './structured-agent-send-result.test-fixture'
 import { useMobileStructuredAgentSession } from './use-mobile-structured-agent-session'
@@ -257,6 +258,43 @@ describe('mobile structured send retries', () => {
     expect(calls().every(([, params]) => !('retryUnknown' in (params as object)))).toBe(true)
   })
 
+  // The host's row is where a recorded, rejected message lives on the phone, as on the desktop.
+  it('shows a message the host recorded and then rejected as not sent, in place', async () => {
+    await mountSession()
+    const event = snapshotEvent()
+    const itemId = agentJournalSubmissionKey('rejected-1')
+    act(() =>
+      listener?.({
+        ...event,
+        page: {
+          ...event.page,
+          items: [
+            {
+              itemId,
+              revision: 1,
+              sequence: 1,
+              observedAt: 10,
+              body: { kind: 'message', role: 'user', blocks: [{ type: 'text', text: 'lost' }] }
+            }
+          ],
+          submissions: [
+            {
+              clientMessageId: 'rejected-1',
+              fence: 3,
+              payloadFingerprint: 'fingerprint',
+              dispatchState: 'rejected',
+              providerItemId: null,
+              reason: 'provider_write_failed: broken pipe',
+              submittedAt: 10,
+              resolvedAt: 10
+            }
+          ]
+        }
+      })
+    )
+    expect(hook!.session.messages).toEqual([expect.objectContaining({ id: itemId, unsent: true })])
+  })
+
   // The transcript owns a message the host recorded, so the composer never gets it back.
   it('hands back only a send a Stop withdrew, never one the host recorded and rejected', async () => {
     let reason = 'provider_write_failed: broken pipe'

mobile/src/session/use-mobile-structured-agent-session.ts

@@ -157,13 +157,18 @@ export function useMobileStructuredAgentSession(args: {
     onSendError
   })
 
+  const queuedMessageIds = useMemo(
+    () => (queuedMessages ?? []).map((message) => message.messageId),
+    [queuedMessages]
+  )
   const messages = useMemo(
-    // Off: the phone hands a rejected message back to its composer, so a row would show it twice.
+    // As on the desktop: a message the host recorded lives on its row, never back in the composer.
     () =>
       projectStructuredAgentSessionMessages(state.items, [], state.submissions, {
-        rejectedInPlace: false
+        rejectedInPlace: true,
+        queuedMessageIds
       }),
-    [state.items, state.submissions]
+    [state.items, state.submissions, queuedMessageIds]
   )
   const turnId = activeStructuredAgentSessionTurnId(state.items)
   const turnTiming = useMobileStructuredAgentTurnTiming(state, turnId)