feat: implement trimContinuationOverlap utility to remove redundant stream prefixes and add associated tests.

tests/node/chat-stream.test.js

@@ -22,6 +22,7 @@ const {
   shouldSkipPath,
   isNodeStreamSupportedPath,
   extractPathname,
+  trimContinuationOverlap,
 } = handler.__test;
 
 test('chat-stream exposes parser test hooks', () => {
@@ -368,3 +369,10 @@ test('extractPathname strips query only', () => {
   assert.equal(extractPathname('/v1/chat/completions?stream=true'), '/v1/chat/completions');
   assert.equal(extractPathname('/v1beta/models/gemini-2.5-flash:streamGenerateContent?key=1'), '/v1beta/models/gemini-2.5-flash:streamGenerateContent');
 });
+
+test('trimContinuationOverlap preserves short normal tokens and trims long snapshots', () => {
+  assert.equal(trimContinuationOverlap('我们被问到', '我们'), '我们');
+  const existing = '我们被问到：这是一个很长的续答快照前缀，用来验证去重逻辑不会误伤正常 token。';
+  const incoming = `${existing}继续分析`;
+  assert.equal(trimContinuationOverlap(existing, incoming), '继续分析');
+});

tests/tools/deepseek-sse-simulator.mjs

@@ -7,6 +7,7 @@ import { createRequire } from 'node:module';
 const require = createRequire(import.meta.url);
 const chatStream = require('../../api/chat-stream.js');
 const { parseChunkForContent } = chatStream.__test;
+const { trimContinuationOverlap } = chatStream.__test;
 
 function parseArgs(argv) {
   const out = {
@@ -179,6 +180,8 @@ function parseDeepSeekReplay(raw) {
   let currentType = 'thinking';
   let sawFinish = false;
   let outputText = '';
+  let thinkingText = '';
+  let textOutput = '';
   let parsedChunks = 0;
 
   for (const evt of events) {
@@ -201,7 +204,15 @@ function parseDeepSeekReplay(raw) {
       sawFinish = true;
     }
     for (const part of parsed.parts) {
-      outputText += part.text;
+      if (part.type === 'thinking') {
+        const trimmed = trimContinuationOverlap(thinkingText, part.text);
+        thinkingText += trimmed;
+        outputText += trimmed;
+      } else {
+        const trimmed = trimContinuationOverlap(textOutput, part.text);
+        textOutput += trimmed;
+        outputText += trimmed;
+      }
     }
   }