fix(kosong): recognize OpenAI-compatible tool_call_id 400 as a recoverable tool-exchange error

.changeset/moonshot-tool-call-id-recovery.md

@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kosong": patch
+---
+
+Recognize the OpenAI-compatible (Moonshot / Kimi) `tool_call_id ... is not found` 400 as a recoverable tool-exchange structural error, so the post-400 strict-resend fallback fires and un-bricks the session instead of failing every subsequent turn with the same error.

packages/agent-core/test/loop/tool-exchange-fallback.e2e.test.ts

@@ -28,6 +28,10 @@ const ADJACENCY_400 = new APIStatusError(
     '`tool_result` block in the next message.',
 );
 
+// The OpenAI-compatible (Moonshot / Kimi) phrasing of the same tool-exchange
+// structural rejection. Verbatim from the field, doubled space included.
+const MOONSHOT_TOOL_CALL_ID_400 = new APIStatusError(400, '400 tool_call_id  is not found');
+
 function userMessage(text: string): Message {
   return { role: 'user', content: [{ type: 'text', text }], toolCalls: [] };
 }
@@ -81,6 +85,19 @@ describe('executeLoopStep — tool exchange adjacency fallback', () => {
     expect(llm.calls[1]?.messages).toBe(strictMessages);
   });
 
+  it('resends once and recovers after a Moonshot tool_call_id-not-found 400', async () => {
+    const { input, llm, strictCalls, strictMessages } = makeHarness(MOONSHOT_TOOL_CALL_ID_400);
+
+    const result = await runTurn(input);
+
+    expect(result.stopReason).toBe('end_turn');
+    // Exactly two provider calls: the rejected one and the strict resend.
+    expect(llm.callCount).toBe(2);
+    expect(strictCalls.count).toBe(1);
+    expect(llm.calls[0]?.messages).toEqual([userMessage('normal projection')]);
+    expect(llm.calls[1]?.messages).toBe(strictMessages);
+  });
+
   it('does not resend for an unrelated 400 — the error propagates and strict is untouched', async () => {
     const { input, llm, strictCalls } = makeHarness(new APIStatusError(400, 'Bad request'));
 

packages/kosong/src/errors.ts

@@ -170,16 +170,25 @@ export function isContextOverflowStatusError(statusCode: number, message: string
   return CONTEXT_OVERFLOW_MESSAGE_PATTERNS.some((pattern) => pattern.test(lowerMessage));
 }
 
-// Strict providers (Anthropic) reject a request whose assistant `tool_use` and
-// `tool_result` blocks are not correctly paired and adjacent — a missing result,
-// a stray result with no matching call, or a result that does not immediately
-// follow its call. The validation runs before any generation, so the error is a
-// non-retryable 4xx. A caller can react by resending a re-projected, strictly
-// wire-compliant request rather than leaving the session permanently stuck.
+// Strict providers reject a request whose assistant `tool_use`/`tool_calls` and
+// `tool_result`/`tool` blocks are not correctly paired and adjacent — a missing
+// result, a stray result with no matching call, or a result that does not
+// immediately follow its call. Anthropic phrases this in terms of
+// `tool_use`/`tool_result`; OpenAI-compatible providers (Moonshot / Kimi) phrase
+// it as a `tool_call_id` that "is not found" in the preceding assistant message.
+// The validation runs before any generation, so the error is a non-retryable
+// 4xx. A caller can react by resending a re-projected, strictly wire-compliant
+// request rather than leaving the session permanently stuck.
 const TOOL_EXCHANGE_ADJACENCY_MESSAGE_PATTERNS = [
   /tool_use[\s\S]*tool_result/,
   /tool_result[\s\S]*tool_use/,
   /unexpected\s+`?tool_result/,
+  // OpenAI-compatible (Moonshot / Kimi): a `tool` message references a
+  // `tool_call_id` with no matching `tool_calls` entry in the preceding
+  // assistant message. Observed verbatim as `tool_call_id  is not found`
+  // (doubled space). Anchored on `tool_call_id` so an unrelated "not found"
+  // (e.g. a 404-style body) cannot trip the recovery.
+  /tool_call_id[\s\S]*not found/,
 ] as const;
 
 export function isToolExchangeAdjacencyError(error: unknown): boolean {

packages/kosong/test/errors.test.ts

@@ -246,11 +246,35 @@ describe('isToolExchangeAdjacencyError', () => {
     );
   });
 
+  // The exact OpenAI-compatible (Moonshot / Kimi) message observed in the field
+  // when a `tool` message's `tool_call_id` has no matching `tool_calls` entry in
+  // the preceding assistant message. The doubled space is verbatim from the
+  // provider.
+  const MOONSHOT_TOOL_CALL_ID_NOT_FOUND = '400 tool_call_id  is not found';
+
+  it('matches the OpenAI/Moonshot tool_call_id-not-found 400', () => {
+    expect(
+      isToolExchangeAdjacencyError(new APIStatusError(400, MOONSHOT_TOOL_CALL_ID_NOT_FOUND)),
+    ).toBe(true);
+    expect(
+      isToolExchangeAdjacencyError(new APIStatusError(400, "tool_call_id 'call_abc123' is not found")),
+    ).toBe(true);
+  });
+
+  it('also matches a 422 tool_call_id-not-found', () => {
+    expect(
+      isToolExchangeAdjacencyError(new APIStatusError(422, MOONSHOT_TOOL_CALL_ID_NOT_FOUND)),
+    ).toBe(true);
+  });
+
   it('does not match a context-overflow 400 or unrelated errors', () => {
     expect(
       isToolExchangeAdjacencyError(new APIContextOverflowError(400, 'context length exceeded')),
     ).toBe(false);
     expect(isToolExchangeAdjacencyError(new APIStatusError(400, 'Bad request'))).toBe(false);
+    // A bare "not found" without a tool_call_id anchor must not match, so an
+    // unrelated 404-style body cannot trip the tool-exchange recovery.
+    expect(isToolExchangeAdjacencyError(new APIStatusError(400, 'resource not found'))).toBe(false);
     expect(isToolExchangeAdjacencyError(new APIStatusError(500, ANTHROPIC_MISSING_RESULT))).toBe(
       false,
     );
@@ -268,6 +292,12 @@ describe('isRecoverableRequestStructureError', () => {
     ).toBe(true);
   });
 
+  it('matches the OpenAI/Moonshot tool_call_id-not-found 400', () => {
+    expect(
+      isRecoverableRequestStructureError(new APIStatusError(400, '400 tool_call_id  is not found')),
+    ).toBe(true);
+  });
+
   it('matches empty / whitespace-only text content rejections', () => {
     expect(
       isRecoverableRequestStructureError(