fix: emit abort event and cancel existing mock streams

- Emit stream-abort event when stopping mock streams to mirror real streaming behavior
- Cancel any existing stream before starting a new one to prevent timer corruption
- Addresses Codex review comments about mock stream lifecycle management

Change-Id: I0a95493aa15dc0eda71a5c31b09b3844eeaf8187
Signed-off-by: Thomas Kosiewski <tk@coder.com>

Author: ThomasK33

src/services/mock/mockScenarioPlayer.ts

@@ -40,9 +40,20 @@ export class MockScenarioPlayer {
   stop(workspaceId: string): void {
     const active = this.activeStreams.get(workspaceId);
     if (!active) return;
+
+    // Clear all pending timers
     for (const timer of active.timers) {
       clearTimeout(timer);
     }
+
+    // Emit stream-abort event to mirror real streaming behavior
+    this.deps.aiService.emit("stream-abort", {
+      type: "stream-abort",
+      workspaceId,
+      messageId: active.messageId,
+      reason: "user_cancelled",
+    });
+
     this.activeStreams.delete(workspaceId);
   }
 
@@ -91,6 +102,11 @@ export class MockScenarioPlayer {
     }
     historySequence = assistantMessage.metadata?.historySequence ?? historySequence;
 
+    // Cancel any existing stream before starting a new one
+    if (this.isStreaming(workspaceId)) {
+      this.stop(workspaceId);
+    }
+
     this.scheduleEvents(workspaceId, turn, historySequence);
     this.turnIndex += 1;
     return Ok(undefined);