Fix optimistic user message reconciliation

packages/app/src/timeline/session-stream-reducers.test.ts

@@ -326,7 +326,7 @@ describe("processTimelineResponse", () => {
             ...makeTimelineEntry(1, "Analyze this", "user_message"),
             item: {
               type: "user_message",
-              text: "Analyze this",
+              text: "server-rendered attachment text",
               messageId: "canonical-create-user",
             },
           },
@@ -339,6 +339,7 @@ describe("processTimelineResponse", () => {
     expect(userMessages[0]).toMatchObject({
       id: "canonical-create-user",
       text: "Analyze this",
+      timestamp: new Date(1000),
       images: [image],
       attachments: [attachment],
     });

packages/app/src/timeline/session-stream-reducers.ts

@@ -295,16 +295,15 @@ function mergeCanonicalUserWithOptimistic(
   canonical: UserMessageItem,
   optimistic: UserMessageItem,
 ): UserMessageItem {
-  const shouldPreserveImages =
-    (!canonical.images || canonical.images.length === 0) &&
-    Boolean(optimistic.images && optimistic.images.length > 0);
-  const shouldPreserveAttachments =
-    (!canonical.attachments || canonical.attachments.length === 0) &&
-    Boolean(optimistic.attachments && optimistic.attachments.length > 0);
   return {
-    ...canonical,
-    ...(shouldPreserveImages ? { images: optimistic.images } : {}),
-    ...(shouldPreserveAttachments ? { attachments: optimistic.attachments } : {}),
+    kind: "user_message",
+    id: canonical.id,
+    text: optimistic.text,
+    timestamp: optimistic.timestamp,
+    ...(optimistic.images && optimistic.images.length > 0 ? { images: optimistic.images } : {}),
+    ...(optimistic.attachments && optimistic.attachments.length > 0
+      ? { attachments: optimistic.attachments }
+      : {}),
   };
 }