fix(ai): let assistant messages fill chat width

src/components/AIChat/ChatExplorer.vue

@@ -367,6 +367,7 @@ watch(
               :class="{
                 'flex min-h-full flex-col justify-center px-4 pb-32 pt-4 space-y-0!':
                   messages.length === 0 && !isAIThinking,
+                'px-4': messages.length > 0 || isAIThinking,
               }"
             >
               <!-- 空状态 Hero 区域 -->
@@ -509,7 +510,7 @@ watch(
 
           <!-- 输入框区域 -->
           <div class="px-4 pb-2">
-            <div class="mx-auto max-w-3xl">
+            <div class="mx-auto max-w-[740px]">
               <AIChatInput
                 ref="chatInputRef"
                 :session-id="sessionId"

src/components/AIChat/chat/ChatMessage.planValidation.test.ts

@@ -3,6 +3,15 @@ import { readFileSync } from 'node:fs'
 import { describe, it } from 'node:test'
 
 describe('ChatMessage plan validation rendering', () => {
+  it('lets assistant messages fill the available row while keeping user bubbles constrained', () => {
+    const source = readFileSync(new URL('./ChatMessage.vue', import.meta.url), 'utf8')
+
+    assert.ok(
+      source.includes("isUser && !isEditing ? 'max-w-[85%] min-w-0' : 'w-full min-w-0'"),
+      'assistant messages should use full width while user messages keep the existing max width'
+    )
+  })
+
   it('does not render a manual step number inside the ordered validation list', () => {
     const source = readFileSync(new URL('./ChatMessage.vue', import.meta.url), 'utf8')
     const validationSection = source.slice(

src/components/AIChat/chat/ChatMessage.vue

@@ -457,7 +457,7 @@ async function handleCopyMarkdown() {
     :class="[isUser && !isEditing ? 'flex-row-reverse' : '', isSummary ? 'justify-center' : '']"
   >
     <!-- 消息内容 -->
-    <div :class="[isSummary || isEditing ? 'w-full min-w-0' : 'max-w-[85%] min-w-0']">
+    <div :class="[isUser && !isEditing ? 'max-w-[85%] min-w-0' : 'w-full min-w-0']">
       <!-- System 消息：可折叠的上下文总结 -->
       <template v-if="isSummary">
         <details

src/composables/useScreenCapture.ts

@@ -141,7 +141,7 @@ export function useScreenCapture() {
     const originalMinWidth = element.style.minWidth
     const originalMaxWidth = element.style.maxWidth
 
-    element.style.padding = '16px'
+    element.style.padding = '16px 40px'
     element.style.paddingBottom = '48px' // 为水印留出空间
     const computedPosition = window.getComputedStyle(element).position
     if (computedPosition === 'static') {