fix: persist mock stream messages to history on completion

- Call HistoryService.updateHistory when stream-end fires in mock mode
- Mirrors real StreamManager behavior to persist completed messages
- Prevents empty assistant entries in chat.jsonl after mock runs
- Addresses Codex review comment about mock persistence

Change-Id: I4f4cd7fe27355a561cd4e2193a4045424918dd1e
Signed-off-by: Thomas Kosiewski <tk@coder.com>

Author: ThomasK33

src/services/mock/mockScenarioPlayer.ts

@@ -125,18 +125,18 @@ export class MockScenarioPlayer {
 
     for (const event of turn.assistant.events) {
       const timer = setTimeout(() => {
-        this.dispatchEvent(workspaceId, event, turn.assistant.messageId, historySequence);
+        void this.dispatchEvent(workspaceId, event, turn.assistant.messageId, historySequence);
       }, event.delay);
       timers.push(timer);
     }
   }
 
-  private dispatchEvent(
+  private async dispatchEvent(
     workspaceId: string,
     event: MockAssistantEvent,
     messageId: string,
     historySequence: number
-  ): void {
+  ): Promise<void> {
     switch (event.kind) {
       case "stream-start": {
         const payload: StreamStartEvent = {
@@ -216,6 +216,34 @@ export class MockScenarioPlayer {
           },
           parts: event.parts,
         };
+
+        // Update history with completed message (mirrors real StreamManager behavior)
+        // Fetch the current message from history to get its historySequence
+        const historyResult = await this.deps.historyService.getHistory(workspaceId);
+        if (historyResult.success) {
+          const existingMessage = historyResult.data.find((msg) => msg.id === messageId);
+          if (existingMessage?.metadata?.historySequence !== undefined) {
+            const completedMessage: CmuxMessage = {
+              id: messageId,
+              role: "assistant",
+              parts: event.parts,
+              metadata: {
+                ...existingMessage.metadata,
+                model: event.metadata.model,
+                systemMessageTokens: event.metadata.systemMessageTokens,
+              },
+            };
+            const updateResult = await this.deps.historyService.updateHistory(
+              workspaceId,
+              completedMessage
+            );
+
+            if (!updateResult.success) {
+              console.error(`Failed to update history for ${messageId}: ${updateResult.error}`);
+            }
+          }
+        }
+
         this.deps.aiService.emit("stream-end", payload);
         this.cleanup(workspaceId);
         break;