fix(chat): stabilize message identities

src/stores/chat/__tests__/chat-history-flow.test.ts

@@ -38,13 +38,13 @@ describe("chat history flow", () => {
       resolveNetwork = resolve;
     });
     const localMessage: UiMessage = {
-      id: "local-msg",
+      displayId: "local-msg",
       content: "cached local message",
       isFromAI: true,
       date: "2026-07-02",
     };
     const networkMessage: UiMessage = {
-      id: "network-msg",
+      displayId: "network-msg",
       content: "fresh network message",
       isFromAI: true,
       date: "2026-07-02",
@@ -67,6 +67,7 @@ describe("chat history flow", () => {
               type: "ChatNetworkHistoryLoaded",
               output: {
                 messages: [networkMessage],
+                localDisplayIds: [localMessage.displayId],
                 localOverwritten: true,
                 localCount: 1,
                 networkCount: 1,
@@ -89,17 +90,17 @@ describe("chat history flow", () => {
     );
 
     expect(actor.getSnapshot().context.messages).toMatchObject([
-      { id: "local-msg", content: "cached local message" },
+      { displayId: "local-msg", content: "cached local message" },
     ]);
 
     resolveNetwork();
     await waitFor(
       actor,
-      (snapshot) => snapshot.context.messages[0]?.id === "network-msg",
+      (snapshot) => snapshot.context.messages[0]?.displayId === "network-msg",
     );
 
     expect(actor.getSnapshot().context.messages).toMatchObject([
-      { id: "network-msg", content: "fresh network message" },
+      { displayId: "network-msg", content: "fresh network message" },
     ]);
 
     actor.stop();
@@ -108,7 +109,7 @@ describe("chat history flow", () => {
   it("loads older pages until total is exhausted and keeps existing messages", async () => {
     const requests: LoadMoreHistoryActorEvent[] = [];
     const latestMessage: UiMessage = {
-      id: "latest",
+      displayId: "latest",
       content: "current unlocked message",
       isFromAI: true,
       date: "2026-07-15",
@@ -173,8 +174,8 @@ describe("chat history flow", () => {
     );
     expect(requests[0]).toMatchObject({ offset: 50, limit: 50 });
     expect(actor.getSnapshot().context.messages).toMatchObject([
-      { id: "older-50" },
-      { id: "latest", content: "current unlocked message" },
+      { displayId: "older-50" },
+      { displayId: "latest", content: "current unlocked message" },
     ]);
 
     actor.send({ type: "ChatLoadMoreHistoryRequested" });
@@ -290,10 +291,10 @@ describe("chat history flow", () => {
   });
 });
 
-function createHistoryMessage(id: string): UiMessage {
+function createHistoryMessage(displayId: string): UiMessage {
   return {
-    id,
-    content: `Message ${id}`,
+    displayId,
+    content: `Message ${displayId}`,
     isFromAI: true,
     date: "2026-07-15",
   };