fix: tolerate anthropic relays that omit text deltas

.changeset/anthropic-relay-missing-text-crash.md

@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Fix a crash when an Anthropic-compatible relay streams a text block without a text field.

apps/kimi-code/src/tui/controllers/session-event-handler.ts

@@ -551,8 +551,9 @@ export class SessionEventHandler {
     // moon spinner while no ThinkingComponent is ever created (it needs visible
     // text), leaving a blank, spinner-less gap until the first real text/tool
     // token arrives. Keep the moon up until actual thinking text shows up.
-    if (event.delta.trim().length === 0 && !streamingUI.hasThinkingDraft()) return;
-    streamingUI.appendThinkingDelta(event.delta);
+    const delta = typeof event.delta === 'string' ? event.delta : '';
+    if (delta.trim().length === 0 && !streamingUI.hasThinkingDraft()) return;
+    streamingUI.appendThinkingDelta(delta);
     this.host.patchLivePane({ mode: 'idle' });
     if (state.appState.streamingPhase !== 'thinking') {
       this.host.setAppState({ streamingPhase: 'thinking', streamingStartTime: Date.now() });
@@ -562,15 +563,19 @@ export class SessionEventHandler {
 
   private handleAssistantDelta(event: AssistantDeltaEvent): void {
     const { state, streamingUI } = this.host;
+    // A compatible relay may stream a text block whose `text` field is absent;
+    // the wire event then carries no `delta` at all. Coerce it to an empty
+    // string so a malformed record can never crash the renderer.
+    const delta = typeof event.delta === 'string' ? event.delta : '';
     if (streamingUI.hasThinkingDraft()) {
       streamingUI.flushThinkingToTranscript('idle');
     }
 
-    if (event.delta.trim().length > 0) {
+    if (delta.trim().length > 0) {
       this.currentTurnHasAssistantText = true;
       this.pendingModelBlockedFallback = undefined;
     }
-    streamingUI.appendAssistantDelta(event.delta);
+    streamingUI.appendAssistantDelta(delta);
 
     this.host.patchLivePane({
       mode: 'idle',

packages/agent-core-v2/src/kosong/provider/bases/anthropic/anthropic.ts

@@ -691,7 +691,7 @@ class AnthropicStreamedMessage implements StreamedMessage {
           const blockIndex = blockEvt.index;
           switch (block.type) {
             case 'text':
-              yield { type: 'text', text: block.text };
+              yield { type: 'text', text: block.text ?? '' };
               break;
             case 'thinking':
               yield { type: 'think', think: block.thinking ?? '' };
@@ -720,7 +720,7 @@ class AnthropicStreamedMessage implements StreamedMessage {
           const blockIndex = deltaEvt.index;
           switch (delta.type) {
             case 'text_delta':
-              yield { type: 'text', text: delta.text };
+              yield { type: 'text', text: delta.text ?? '' };
               break;
             case 'thinking_delta':
               yield { type: 'think', think: delta.thinking ?? '' };

packages/kosong/src/providers/anthropic.ts

@@ -809,7 +809,7 @@ class AnthropicStreamedMessage implements StreamedMessage {
           // eslint-disable-next-line typescript-eslint/switch-exhaustiveness-check
           switch (block.type) {
             case 'text':
-              yield { type: 'text', text: block.text };
+              yield { type: 'text', text: block.text ?? '' };
               break;
             case 'thinking':
               yield { type: 'think', think: block.thinking ?? '' };
@@ -842,7 +842,7 @@ class AnthropicStreamedMessage implements StreamedMessage {
           // eslint-disable-next-line typescript-eslint/switch-exhaustiveness-check
           switch (delta.type) {
             case 'text_delta':
-              yield { type: 'text', text: delta.text };
+              yield { type: 'text', text: delta.text ?? '' };
               break;
             case 'thinking_delta':
               yield { type: 'think', think: delta.thinking ?? '' };

packages/kosong/test/anthropic.test.ts

@@ -2816,6 +2816,40 @@ describe('AnthropicChatProvider', () => {
       });
     });
 
+    it('coerces a missing text field to an empty string for relays that omit it', async () => {
+      const provider = createStreamProvider();
+      const stream = mockStream([
+        {
+          type: 'message_start',
+          message: {
+            id: 'msg_stream_002',
+            usage: { input_tokens: 10 },
+          },
+        },
+        { type: 'content_block_start', index: 0, content_block: { type: 'text' } },
+        { type: 'content_block_delta', index: 0, delta: { type: 'text_delta' } },
+        { type: 'content_block_delta', index: 0, delta: { type: 'text_delta', text: 'ok' } },
+        { type: 'message_delta', delta: {}, usage: { output_tokens: 5 } },
+        { type: 'message_stop' },
+      ]);
+
+      (provider as any)._client.messages.create = vi.fn().mockResolvedValue(stream) as never;
+
+      const result = await provider.generate(
+        '',
+        [],
+        [{ role: 'user', content: [{ type: 'text', text: 'Hi' }], toolCalls: [] }],
+      );
+
+      const parts = await collectParts(result);
+
+      expect(parts).toEqual([
+        { type: 'text', text: '' },
+        { type: 'text', text: '' },
+        { type: 'text', text: 'ok' },
+      ]);
+    });
+
     it('yields thinking delta and signature from stream events', async () => {
       const provider = createStreamProvider();
       const stream = mockStream([