fix: drop empty text blocks during projection (#910)

.changeset/clean-empty-text-blocks.md

@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Fix provider requests failing when restored conversation history contains empty text content blocks.

packages/agent-core/src/agent/context/projector.ts

@@ -1,23 +1,18 @@
 import type { ContentPart, Message, TextPart } from '@moonshot-ai/kosong';
 
+import { ErrorCodes, KimiError } from '../../errors';
 import type { ContextMessage } from './types';
 
 export function project(history: readonly ContextMessage[]): Message[] {
-  // Keep partial or empty assistant placeholders away from providers.
-  // They can appear when a turn is aborted or errors before any content
-  // or tool call is appended.
-  const usable = history.filter((message) => {
-    return (
-      message.partial !== true &&
-      !(message.role === 'assistant' && message.content.length === 0 && message.toolCalls.length === 0)
-    );
-  });
-  return mergeAdjacentUserMessages(usable);
+  return mergeAdjacentUserMessages(history);
 }
 
 function mergeAdjacentUserMessages(history: readonly ContextMessage[]): Message[] {
   const out: ContextMessage[] = [];
-  for (const message of history) {
+  for (const source of history) {
+    const message = prepareMessageForProjection(source);
+    if (message === null) continue;
+
     const previous = out.at(-1);
     if (
       canMergeUserMessage(message) &&
@@ -32,6 +27,33 @@ function mergeAdjacentUserMessages(history: readonly ContextMessage[]): Message[
   return out.map(stripContextMetadata);
 }
 
+function prepareMessageForProjection(message: ContextMessage): ContextMessage | null {
+  if (message.partial === true) return null;
+
+  let content: ContentPart[] | undefined;
+  for (const [index, part] of message.content.entries()) {
+    if (part.type === 'text' && part.text.length === 0) {
+      content ??= message.content.slice(0, index);
+      continue;
+    }
+    content?.push(part);
+  }
+
+  const next = content === undefined ? message : { ...message, content };
+  if (next.role === 'tool' && next.content.length === 0) {
+    throw new KimiError(
+      ErrorCodes.REQUEST_INVALID,
+      'Tool result message content cannot be empty after removing empty text blocks.',
+      {
+        details: {
+          toolCallId: next.toolCallId,
+        },
+      },
+    );
+  }
+  return next.content.length === 0 && next.toolCalls.length === 0 ? null : next;
+}
+
 function canMergeUserMessage(message: ContextMessage): boolean {
   return message.role === 'user' && message.origin?.kind === 'user';
 }

packages/agent-core/test/agent/context.test.ts

@@ -80,6 +80,87 @@ describe('Agent context', () => {
     ]);
   });
 
+  it('drops empty text parts only in LLM projection', () => {
+    const history: ContextMessage[] = [
+      {
+        role: 'user',
+        content: [
+          { type: 'text', text: '' },
+          { type: 'text', text: 'Run the tool' },
+        ],
+        toolCalls: [],
+      },
+      {
+        role: 'assistant',
+        content: [{ type: 'text', text: '' }],
+        toolCalls: [],
+      },
+      {
+        role: 'assistant',
+        content: [{ type: 'text', text: '' }],
+        toolCalls: [{ type: 'function', id: 'call_empty', name: 'empty', arguments: '{}' }],
+      },
+      {
+        role: 'assistant',
+        content: [{ type: 'think', think: '', encrypted: 'enc_empty_thinking' }],
+        toolCalls: [],
+      },
+      {
+        role: 'user',
+        content: [{ type: 'text', text: '   ' }],
+        toolCalls: [],
+      },
+    ];
+
+    expect(project(history)).toEqual([
+      {
+        role: 'user',
+        content: [{ type: 'text', text: 'Run the tool' }],
+        toolCalls: [],
+      },
+      {
+        role: 'assistant',
+        content: [],
+        toolCalls: [{ type: 'function', id: 'call_empty', name: 'empty', arguments: '{}' }],
+      },
+      {
+        role: 'assistant',
+        content: [{ type: 'think', think: '', encrypted: 'enc_empty_thinking' }],
+        toolCalls: [],
+      },
+      {
+        role: 'user',
+        content: [{ type: 'text', text: '   ' }],
+        toolCalls: [],
+      },
+    ]);
+    expect(history[0]?.content).toEqual([
+      { type: 'text', text: '' },
+      { type: 'text', text: 'Run the tool' },
+    ]);
+    expect(history[1]?.content).toEqual([{ type: 'text', text: '' }]);
+  });
+
+  it('rejects tool result messages left empty by LLM projection cleanup', () => {
+    const history: ContextMessage[] = [
+      {
+        role: 'assistant',
+        content: [],
+        toolCalls: [{ type: 'function', id: 'call_empty', name: 'empty', arguments: '{}' }],
+      },
+      {
+        role: 'tool',
+        content: [{ type: 'text', text: '' }],
+        toolCallId: 'call_empty',
+        toolCalls: [],
+      },
+    ];
+
+    expect(() => project(history)).toThrow(
+      'Tool result message content cannot be empty after removing empty text blocks.',
+    );
+  });
+
   it('projects hook result messages into LLM projection', async () => {
     const ctx = testAgent();
     ctx.configure();