fix(agent-core-v2): restore thinking for the openrouter reasoning dialect (#3910)

Keep string reasoning fields when a reasoning_details array is present, stamp each think part by source, and replay those fields on the next request.

Author: sailist

.changeset/openrouter-reasoning-display.md

@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Restore thinking display for OpenAI-compatible providers that send a reasoning string next to an unrecognized reasoning_details array.

packages/agent-core-v2/docs/state-manifest.d.ts

@@ -730,6 +730,7 @@ export interface AgentStateSnapshot {
       encrypted?: string;
       detailsIndex?: number;
       hidden?: boolean;
+      reasoningKey?: string;
     } | /* ImageURLPart — packages/agent-core-v2/src/human/llm/message.ts */ {
       type: 'image_url';
       imageUrl: {
@@ -1027,6 +1028,7 @@ export interface AgentStateSnapshot {
     encrypted?: string;
     detailsIndex?: number;
     hidden?: boolean;
+    reasoningKey?: string;
   } | /* ImageURLPart — packages/agent-core-v2/src/human/llm/message.ts */ {
     type: 'image_url';
     imageUrl: {

packages/agent-core-v2/src/agent/loop/loopService.ts

@@ -1426,6 +1426,7 @@ export class AgentLoopService extends Disposable implements IAgentLoopService {
               encrypted: delta.encrypted,
               detailsIndex: delta.detailsIndex,
               hidden: delta.hidden,
+              reasoningKey: delta.reasoningKey,
             });
             if (part?.type === 'think' && part.hidden === true) return;
             void this.dispatcher.dispatch(

packages/agent-core-v2/src/agent/loop/machine/engine.ts

@@ -40,6 +40,7 @@ export type MachineEngineDelta =
       readonly encrypted?: string;
       readonly detailsIndex?: number;
       readonly hidden?: boolean;
+      readonly reasoningKey?: string;
     }
   | {
       readonly kind: 'toolCall';
@@ -227,6 +228,7 @@ function createDeltaSplitter(): (part: StreamedMessagePart) => MachineEngineDelt
           encrypted: part.encrypted,
           detailsIndex: part.detailsIndex,
           hidden: part.hidden,
+          reasoningKey: part.reasoningKey,
         };
       case 'image_url':
       case 'audio_url':

packages/agent-core-v2/src/human/agent/historySchema.ts

@@ -10,6 +10,7 @@ const thinkPartSchema = z.object({
   encrypted: z.string().optional(),
   detailsIndex: z.number().optional(),
   hidden: z.boolean().optional(),
+  reasoningKey: z.string().optional(),
 });
 const imageUrlPartSchema = z.object({
   type: z.literal('image_url'),

packages/agent-core-v2/src/human/llm/message.ts

@@ -18,6 +18,7 @@ export interface ThinkPart {
   encrypted?: string;
   detailsIndex?: number;
   hidden?: boolean;
+  reasoningKey?: string;
 }
 
 export interface ImageURLPart {
@@ -111,6 +112,9 @@ export function mergeInPlace(target: StreamedMessagePart, source: StreamedMessag
     if (target.hidden !== source.hidden) {
       return false;
     }
+    if (target.reasoningKey !== source.reasoningKey) {
+      return false;
+    }
     target.think += source.think;
     if (source.encrypted !== undefined) {
       target.encrypted = source.encrypted;

packages/agent-core-v2/src/human/llm/requester/bases/openai/format.ts

@@ -39,8 +39,8 @@ import { lowerMessage } from './lower';
 import { extractToolMedia } from './patterns';
 import {
   convertReasoningDetails,
-  extractReasoning,
   extractReasoningDetails,
+  extractReasoningStrings,
 } from './reasoning-key';
 
 export function responseFormatToOpenAI(format: ResponseFormat): Record<string, unknown> {
@@ -299,23 +299,20 @@ export function createOpenAIFormat(): OpenAIProtocolFormat {
         }
         const reasoningDetails =
           options?.reasoningKey === undefined ? extractReasoningDetails(delta) : undefined;
-        if (reasoningDetails !== undefined) {
-          const inline = extractReasoning(delta, 'reasoning_content');
-          if (inline !== undefined) {
+        for (const reasoning of extractReasoningStrings(delta)) {
+          if (reasoning.key === 'reasoning_content') {
             seenReasoningContent = true;
-            sink.onDelta({ type: 'think', think: inline.value });
           }
+          sink.onDelta({
+            type: 'think',
+            think: reasoning.value,
+            reasoningKey: reasoning.key,
+          });
+        }
+        if (reasoningDetails !== undefined) {
           for (const part of convertReasoningDetails(reasoningDetails, seenReasoningContent)) {
             sink.onDelta(part);
           }
-        } else {
-          const reasoning = extractReasoning(delta);
-          if (reasoning !== undefined) {
-            if (reasoning.key === 'reasoning_content') {
-              seenReasoningContent = true;
-            }
-            sink.onDelta({ type: 'think', think: reasoning.value });
-          }
         }
         if (typeof delta.content === 'string' && delta.content.length > 0) {
           sink.onDelta({ type: 'text', text: delta.content });

packages/agent-core-v2/src/human/llm/requester/bases/openai/lower.ts

@@ -121,19 +121,49 @@ export function lowerMessage(message: Message, lower: OpenAILowerContext): OpenA
     converted = { role: message.role, content: content ?? '' };
   }
   const reasoningDetails: Record<string, unknown>[] = [];
+  const stringFields = new Map<string, string>();
+  let unstamped = '';
+  let hasUnstamped = false;
   for (const part of message.content) {
-    if (part.type !== 'think' || part.detailsIndex === undefined) continue;
-    if (part.think.length > 0) {
-      reasoningDetails.push({ type: 'summary', summary: part.think });
+    if (part.type !== 'think') continue;
+    if (part.detailsIndex !== undefined) {
+      if (part.think.length > 0) {
+        reasoningDetails.push({ type: 'summary', summary: part.think });
+      }
+      if (part.encrypted !== undefined) {
+        reasoningDetails.push({ type: 'encrypted', encrypted: part.encrypted });
+      }
+      continue;
     }
-    if (part.encrypted !== undefined) {
-      reasoningDetails.push({ type: 'encrypted', encrypted: part.encrypted });
+    if (part.reasoningKey !== undefined && part.reasoningKey !== REASONING_DETAILS_KEY) {
+      const current = stringFields.get(part.reasoningKey) ?? '';
+      stringFields.set(
+        part.reasoningKey,
+        part.hidden === true ? current : current + part.think,
+      );
+      continue;
     }
+    hasUnstamped = true;
+    if (part.hidden !== true) {
+      unstamped += part.think;
+    }
+  }
+  if (hasUnstamped) {
+    stringFields.set(reasoningKey, (stringFields.get(reasoningKey) ?? '') + unstamped);
   }
   if (reasoningDetails.length > 0) {
     (converted as Record<string, unknown>)[REASONING_DETAILS_KEY] = reasoningDetails;
-    (converted as Record<string, unknown>)[DEFAULT_REASONING_KEY] = reasoningContent;
-  } else if (hasReasoningPart || (preserveThinking && message.role === 'assistant')) {
+    (converted as Record<string, unknown>)[DEFAULT_REASONING_KEY] =
+      stringFields.get(DEFAULT_REASONING_KEY) ?? reasoningContent;
+  }
+  for (const [key, value] of stringFields) {
+    (converted as Record<string, unknown>)[key] = value;
+  }
+  if (
+    stringFields.size === 0 &&
+    reasoningDetails.length === 0 &&
+    (hasReasoningPart || (preserveThinking && message.role === 'assistant'))
+  ) {
     (converted as Record<string, unknown>)[reasoningKey] = reasoningContent;
   }
   return [converted];

packages/agent-core-v2/src/human/llm/requester/bases/openai/reasoning-key.ts

@@ -10,18 +10,29 @@ export type ReasoningKey = (typeof KNOWN_REASONING_KEYS)[number];
 
 export const DEFAULT_REASONING_KEY: ReasoningKey = KNOWN_REASONING_KEYS[0];
 
+export function extractReasoningStrings(
+  source: unknown,
+): { key: string; value: string }[] {
+  if (typeof source !== 'object' || source === null) return [];
+  const record = source as Record<string, unknown>;
+  const found: { key: string; value: string }[] = [];
+  for (const key of KNOWN_REASONING_KEYS) {
+    const value = record[key];
+    if (typeof value === 'string') found.push({ key, value });
+  }
+  return found;
+}
+
 export function extractReasoning(
   source: unknown,
   explicitKey?: string,
 ): { key: string; value: string } | undefined {
-  if (typeof source !== 'object' || source === null) return undefined;
-  const record = source as Record<string, unknown>;
-  const keys: readonly string[] = explicitKey !== undefined ? [explicitKey] : KNOWN_REASONING_KEYS;
-  for (const key of keys) {
-    const value = record[key];
-    if (typeof value === 'string') return { key, value };
+  if (explicitKey !== undefined) {
+    if (typeof source !== 'object' || source === null) return undefined;
+    const value = (source as Record<string, unknown>)[explicitKey];
+    return typeof value === 'string' ? { key: explicitKey, value } : undefined;
   }
-  return undefined;
+  return extractReasoningStrings(source)[0];
 }
 
 export class ReasoningKeyDialect {
@@ -32,7 +43,7 @@ export class ReasoningKeyDialect {
   observe(source: unknown): string | undefined {
     const found = extractReasoning(source, this._explicitKey);
     if (found === undefined) return undefined;
-    if (this._explicitKey === undefined) {
+    if (this._explicitKey === undefined && this._detected === undefined) {
       this._detected = found.key;
     }
     return found.value;
@@ -92,6 +103,7 @@ export function convertReasoningDetails(
         think: element.summary,
         detailsIndex: element.index,
         hidden: hiddenSummary ? true : undefined,
+        reasoningKey: REASONING_DETAILS_KEY,
       } satisfies ThinkPart);
     }
     if (element.type !== 'summary' && element.encrypted !== undefined && element.encrypted.length > 0) {
@@ -100,6 +112,7 @@ export function convertReasoningDetails(
         think: '',
         encrypted: element.encrypted,
         detailsIndex: element.index,
+        reasoningKey: REASONING_DETAILS_KEY,
       } satisfies ThinkPart);
     }
   }