diff --git a/web/src/components/GraphChatBar.vue b/web/src/components/GraphChatBar.vue
index 840d2f9..1bd7a04 100644
--- a/web/src/components/GraphChatBar.vue
+++ b/web/src/components/GraphChatBar.vue
@@ -50,6 +50,7 @@
 <script setup>
 import { ref, computed, nextTick, watch, onMounted } from 'vue'
 import { marked } from 'marked'
+import { buildOutgoingMessage } from '@/composables/chatContextInjection.js'
 
 const props = defineProps({
   companyId: { type: String, required: true },
@@ -83,11 +84,6 @@ const contextTooltip = computed(() => {
   return `任务 ${c.taskId}《${c.taskTitle}》(${c.taskStatus}) · 目标 ${c.goalId}《${c.goalTitle}》`
 })
 
-function contextKey(c) {
-  if (!c) return ''
-  return `${c.taskId || ''}|${c.goalId || ''}`
-}
-
 function renderMarkdown(text) {
   try { return marked.parse(text || '', { breaks: true, gfm: true }) }
   catch { return (text || '').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/\n/g, '<br>') }
@@ -112,12 +108,8 @@ async function handleSend() {
   const text = inputText.value.trim()
   if (!text || sending.value) return
 
-  const key = contextKey(props.context)
-  let payload = text
-  if (props.context && key !== lastSentContextKey.value) {
-    payload = `[当前上下文] 任务 ${props.context.taskId}《${props.context.taskTitle}》(状态: ${props.context.taskStatus}) · 目标 ${props.context.goalId}《${props.context.goalTitle}》\n\n${text}`
-    lastSentContextKey.value = key
-  }
+  const { payload, nextKey } = buildOutgoingMessage(text, props.context, lastSentContextKey.value)
+  lastSentContextKey.value = nextKey
 
   messages.value.push({ role: 'user', content: text, timestamp: new Date().toISOString() })
   inputText.value = ''
diff --git a/web/src/composables/chatContextInjection.js b/web/src/composables/chatContextInjection.js
new file mode 100644
index 0000000..346baa6
--- /dev/null
+++ b/web/src/composables/chatContextInjection.js
@@ -0,0 +1,37 @@
+/**
+ * 从 GraphChatBar.vue 抽出来的纯逻辑：graph-console 底部聊天条要不要把"当前选中的
+ * task/goal"拼进发给 agent 的消息里。
+ *
+ * 抽成不依赖组件实例的纯函数，是为了能在不挂载整个 Vue 组件的前提下对它做回归测试
+ * （照抄 agentChatEvents.js 的先例）。
+ */
+
+/** context 的身份 key —— 只看 taskId/goalId，title/status 变了不算"context 变了" */
+export function contextKey(context) {
+  if (!context) return '';
+  return `${context.taskId || ''}|${context.goalId || ''}`;
+}
+
+function contextLine(context) {
+  return `[当前上下文] 任务 ${context.taskId}《${context.taskTitle}》(状态: ${context.taskStatus}) · 目标 ${context.goalId}《${context.goalTitle}》`;
+}
+
+/**
+ * 算出实际要发给后端的消息文本。
+ *
+ * context 跟上次发送时不同才在文本前面拼一行说明，agent 不用用户手动复述在看哪个
+ * 任务；没变化就原样发，避免每条消息都重复刷一遍同一句上下文。
+ *
+ * @param {string} text 用户输入的原文（聊天气泡里展示的也是这个，不受影响）
+ * @param {object|null} context 当前选中的 task/goal，见 GraphConsole.vue 的 chatContext
+ * @param {string} lastSentKey 上一次实际发送时的 contextKey()
+ * @returns {{ payload: string, nextKey: string }} payload 是要 POST 的 message 字段；
+ *   nextKey 供调用方回写 lastSentContextKey，没有 context 时透传 lastSentKey 不变
+ */
+export function buildOutgoingMessage(text, context, lastSentKey) {
+  const key = contextKey(context);
+  if (context && key !== lastSentKey) {
+    return { payload: `${contextLine(context)}\n\n${text}`, nextKey: key };
+  }
+  return { payload: text, nextKey: lastSentKey };
+}
diff --git a/web/src/composables/chatContextInjection.test.js b/web/src/composables/chatContextInjection.test.js
new file mode 100644
index 0000000..b6c87ca
--- /dev/null
+++ b/web/src/composables/chatContextInjection.test.js
@@ -0,0 +1,52 @@
+/**
+ * 回归测试：graph-console 底部聊天条的上下文注入不变式——
+ * context 变了才拼上下文行，没变就原样发，不能每条消息都刷一遍。
+ */
+import { describe, it, expect } from 'vitest';
+import { contextKey, buildOutgoingMessage } from './chatContextInjection.js';
+
+const ctxA = { taskId: 'T-1', taskTitle: '任务A', taskStatus: 'running', goalId: 'G-1', goalTitle: '目标A' };
+const ctxB = { taskId: 'T-2', taskTitle: '任务B', taskStatus: 'pending', goalId: 'G-2', goalTitle: '目标B' };
+
+describe('chatContextInjection · buildOutgoingMessage', () => {
+  it('首次发送（lastSentKey 为空）带上下文时要拼上下文行', () => {
+    const { payload, nextKey } = buildOutgoingMessage('你好', ctxA, '');
+    expect(payload).toContain('T-1');
+    expect(payload).toContain('任务A');
+    expect(payload.endsWith('你好')).toBe(true);
+    expect(nextKey).toBe(contextKey(ctxA));
+  });
+
+  it('context 跟上次相同时不重复拼上下文行，原样发送用户文本', () => {
+    const first = buildOutgoingMessage('第一条', ctxA, '');
+    const second = buildOutgoingMessage('第二条', ctxA, first.nextKey);
+    expect(second.payload).toBe('第二条');
+    expect(second.nextKey).toBe(first.nextKey);
+  });
+
+  it('context 换了（task 或 goal 变化）要重新拼一次', () => {
+    const first = buildOutgoingMessage('第一条', ctxA, '');
+    const second = buildOutgoingMessage('切到另一个任务了', ctxB, first.nextKey);
+    expect(second.payload).toContain('T-2');
+    expect(second.payload).toContain('任务B');
+    expect(second.nextKey).toBe(contextKey(ctxB));
+    expect(second.nextKey).not.toBe(first.nextKey);
+  });
+
+  it('没有 context（没选中任务）时原样发送，不拼任何说明', () => {
+    const { payload, nextKey } = buildOutgoingMessage('随便聊聊', null, 'stale-key');
+    expect(payload).toBe('随便聊聊');
+    expect(nextKey).toBe('stale-key'); // 透传，不产生新 key
+  });
+});
+
+describe('chatContextInjection · contextKey', () => {
+  it('null context 的 key 是空字符串', () => {
+    expect(contextKey(null)).toBe('');
+  });
+
+  it('taskId/goalId 相同则 key 相同，跟 title/status 无关', () => {
+    const same = { ...ctxA, taskTitle: '改了标题', taskStatus: 'completed' };
+    expect(contextKey(same)).toBe(contextKey(ctxA));
+  });
+});