fix(chat): pin existing-session sends to captured target (#2424)

* fix(chat): pin sends to captured session

* fix(chat): handle runtime cancellation consistently

packages/ui/src/lib/opencode/client.test.ts

@@ -6,6 +6,7 @@ type ConfigResponse = { data: Record<string, unknown> };
 
 const configResolvers: Array<(response: ConfigResponse) => void> = [];
 let configCalls = 0;
+let runtimeKey = 'test-runtime';
 const promptAsyncCalls: unknown[][] = [];
 const promptAsyncResults: Array<unknown> = [];
 
@@ -44,7 +45,7 @@ mock.module('@/lib/runtime-url', () => ({
 
 mock.module('@/lib/runtime-switch', () => ({
   getRuntimeApiBaseUrl: mock(() => ''),
-  getRuntimeKey: mock(() => 'test-runtime'),
+  getRuntimeKey: mock(() => runtimeKey),
 }));
 
 mock.module('@/lib/runtime-fetch', () => ({
@@ -60,6 +61,7 @@ mock.module('@/lib/startupTrace', () => ({
 const { opencodeClient } = await import(`./client?cache-test=${Date.now()}`);
 
 beforeEach(() => {
+  runtimeKey = 'test-runtime';
   promptAsyncCalls.length = 0;
   promptAsyncResults.length = 0;
 });
@@ -160,4 +162,34 @@ describe('opencodeClient prompt retry behavior', () => {
     expect(promptAsyncCalls.length).toBe(1);
     expect(error instanceof Error ? error.message : String(error)).toContain('Failed to send message (503)');
   });
+
+  test('does not dispatch after the runtime changes while preparing attachments', async () => {
+    runtimeKey = 'runtime-a';
+    const pending = opencodeClient.sendMessage({
+      id: 'ses_runtime_race',
+      providerID: 'runtime-race-provider',
+      modelID: 'model-a',
+      text: 'hello',
+      runtimeKey: 'runtime-a',
+      files: [{
+        type: 'file',
+        mime: 'text/markdown',
+        filename: 'notes.md',
+        url: 'data:text/markdown,hello',
+      }],
+    });
+
+    runtimeKey = 'runtime-b';
+
+    let error: unknown = null;
+    try {
+      await pending;
+    } catch (caught) {
+      error = caught;
+    }
+
+    expect(error).toBeInstanceOf(Error);
+    expect(error instanceof Error ? error.message : String(error)).toContain('runtime changed');
+    expect(promptAsyncCalls).toHaveLength(0);
+  });
 });

packages/ui/src/lib/opencode/client.ts

@@ -269,6 +269,12 @@ class OpencodeService {
     this.client = createRuntimeOpencodeClient({ baseUrl: this.baseUrl });
   }
 
+  private assertRuntimeUnchanged(runtimeKey?: string): void {
+    if (runtimeKey && runtimeKey !== getRuntimeKey()) {
+      throw new Error('Message was not sent because the runtime changed.');
+    }
+  }
+
   getBaseUrl(): string {
     return this.baseUrl;
   }
@@ -744,6 +750,7 @@ class OpencodeService {
   }
 
   async sendMessage(params: {
+    runtimeKey?: string;
     id: string;
     providerID: string;
     modelID: string;
@@ -769,6 +776,8 @@ class OpencodeService {
     };
     directory?: string | null;
   }): Promise<string> {
+    this.assertRuntimeUnchanged(params.runtimeKey);
+
     // Use the optimistic/client-generated ID as the real user message ID so SSE
     // can reconcile the echoed server message in-place.
     const messageId = params.messageId ?? ascendingId("msg");
@@ -852,6 +861,7 @@ class OpencodeService {
     }
 
     assertProviderCircuitClosed(params.providerID);
+    this.assertRuntimeUnchanged(params.runtimeKey);
 
     let response: Response;
 
@@ -918,6 +928,7 @@ class OpencodeService {
   }
 
   async sendCommand(params: {
+    runtimeKey?: string;
     id: string;
     providerID: string;
     modelID: string;
@@ -929,6 +940,8 @@ class OpencodeService {
     messageId?: string;
     directory?: string | null;
   }): Promise<string> {
+    this.assertRuntimeUnchanged(params.runtimeKey);
+
     const tempMessageId = params.messageId ?? ascendingId("msg");
 
     const parts: FilePartInput[] = [];
@@ -939,6 +952,7 @@ class OpencodeService {
     }
 
     const requestDirectory = this.normalizeCandidatePath(params.directory ?? null) ?? this.currentDirectory;
+    this.assertRuntimeUnchanged(params.runtimeKey);
 
     const response = await this.client.session.command({
       sessionID: params.id,
@@ -968,6 +982,7 @@ class OpencodeService {
   }
 
   async shellSession(params: {
+    runtimeKey?: string;
     sessionId: string;
     command: string;
     agent: string;
@@ -975,6 +990,7 @@ class OpencodeService {
     messageId?: string;
     directory?: string | null;
   }): Promise<{ info: Message; parts: Part[] }> {
+    this.assertRuntimeUnchanged(params.runtimeKey);
     const requestDirectory = this.normalizeCandidatePath(params.directory ?? null) ?? this.currentDirectory;
     const response = await this.client.session.shell({
       sessionID: params.sessionId,