fix(backthink): 后台思考静默广播——不再把内部推理泄到聊天思维链 + XML 动作/旁白解析

【静默广播修复（bug：思维链露出 backthink 推理）】
- 根因：LoopThinker.Think 复用同一 loop.Loop 且 loop 全局带 OnStream，backthink 后台思考时
  把 [background autonomous reflection] 的 thinking/流式事件广播到前端，被当聊天思维链显示。
- loop/mute_ctx.go：WithMutedBroadcast(ctx) + isMutedBroadcast(ctx)——context 上静默标志。
- loop 四处广播抑制（stream.go 流式 / step.go 静默走非流式 agentStep / request.go capacity 事件 /
  tools.go tool_execution），静默时跳过 UI 广播，推理照常返回结论。
- thinker.go LoopThinker.Think 用 loop.WithMutedBroadcast(ctx)，backthink 不再泄 thinking。

【XML 动作/旁白结构化解析】
- cyrene.yaml systemPrompt 加「表达方式：动作与旁白」——动作 <action>…</action>、
  旁白 <narration>…</narration>；克制≤1-2个/段、贴合唤醒态、重要信息不加、朗读正文忽略标签。
- 前端 parseContent.ts：ContentPart[]（text/action/narration），非贪婪+反向引用、跨行、非法/
  未闭合兜底纯文本不崩；summarizeContent 供思维导图/状态。
- 前端 renderContent.tsx：action/narration → 灰斜体(mu-text-lo italic)句中原位渲染。
- 应用到 chat.tsx UserBubble/AssistantBubble + messages 各 mode body。

go build/vet/test(loop/backthink)绿 + 前端 tsc/vite 绿。

frontend/web/src/components/chat.tsx

@@ -4,6 +4,7 @@ import { Tag } from "./primitives";
 import { Icon, type IconName } from "./Icon";
 import { WakePath } from "./status";
 import { modeBody } from "./messages";
+import { renderContent } from "../lib/renderContent";
 
 /** Collapsible inline chain-of-thought block. */
 export function ThinkingBlock({
@@ -96,9 +97,9 @@ export function MessageBubble({
 function UserBubble({ message, mode }: { message: ChatMessage; mode: Mode }): React.ReactNode {
   const body: React.ReactNode =
     mode === "code" ? (
-      <pre className="whitespace-pre-wrap font-mono text-xs leading-relaxed">{message.content}</pre>
+      <pre className="whitespace-pre-wrap font-mono text-xs leading-relaxed">{renderContent(message.content)}</pre>
     ) : message.content ? (
-      <span className="whitespace-pre-wrap">{message.content}</span>
+      <span className="whitespace-pre-wrap">{renderContent(message.content)}</span>
     ) : null;
   return (
     <div className="mu-rise-in flex justify-end">

frontend/web/src/components/messages/index.tsx

@@ -4,6 +4,7 @@ import type { ChatMessage, Mode } from "../../lib/types";
 import { Tag } from "../primitives";
 import { Icon } from "../Icon";
 import { useAppStore } from "../../store/useAppStore";
+import { renderContent } from "../../lib/renderContent";
 
 /**
  * Mode-specific assistant message bodies (design/07 §2). The shared outer
@@ -22,7 +23,7 @@ function shell(children: ReactNode): ReactNode {
 
 function fallbackText(message: ChatMessage): ReactNode {
   return message.content ? (
-    <span className="whitespace-pre-wrap">{message.content}</span>
+    <span className="whitespace-pre-wrap">{renderContent(message.content)}</span>
   ) : message.streaming ? (
     <span className="mu-blink text-[var(--mu-text-lo)]">生成中…</span>
   ) : null;
@@ -34,7 +35,7 @@ export function CodeMessageBody({ message }: { message: ChatMessage }): ReactNod
     <div className="space-y-2">
       {message.content ? (
         <pre className="overflow-x-auto whitespace-pre-wrap rounded-[var(--mu-radius-sm)] bg-[var(--mu-surface-2)] p-3 font-mono text-xs leading-relaxed text-[var(--mu-text-mid)]">
-          {message.content}
+          {renderContent(message.content)}
         </pre>
       ) : message.streaming ? (
         <div className="mu-blink text-xs text-[var(--mu-text-lo)]">正在执行 / 生成中…</div>
@@ -51,7 +52,7 @@ export function DocsMessageBody({ message }: { message: ChatMessage }): ReactNod
         <div className="flex items-start gap-2">
           <Icon name="docs" size={18} className="mt-0.5 shrink-0 text-[var(--mu-accent)]" />
           <div className="min-w-0 space-y-1">
-            <div className="text-sm font-medium">{message.content}</div>
+            <div className="text-sm font-medium">{renderContent(message.content)}</div>
             <Tag tone="neutral">知识库</Tag>
           </div>
         </div>
@@ -68,7 +69,7 @@ export function HomeMessageBody({ message }: { message: ChatMessage }): ReactNod
   return (
     <div className="space-y-2">
       {message.content ? (
-        <span className="whitespace-pre-wrap">{message.content}</span>
+        <span className="whitespace-pre-wrap">{renderContent(message.content)}</span>
       ) : null}
       {devices.length > 0 ? (
         <div className="flex flex-wrap gap-2 pt-1">
@@ -97,7 +98,7 @@ export function WorkMessageBody({ message }: { message: ChatMessage }): ReactNod
           {tasks.map((t, i) => (
             <div key={i} className="flex items-center gap-2 text-sm">
               <Icon name="check" size={14} className="shrink-0 text-[var(--mu-ok)]" />
-              <span className="min-w-0 whitespace-pre-wrap">{t}</span>
+              <span className="min-w-0 whitespace-pre-wrap">{renderContent(t)}</span>
             </div>
           ))}
         </div>
@@ -130,7 +131,7 @@ export function VisionMessageBody({ message }: { message: ChatMessage }): ReactN
           {hasImage ? <Tag tone="accent">识别</Tag> : null}
         </div>
         {message.content ? (
-          <span className="whitespace-pre-wrap text-sm text-[var(--mu-text-hi)]">{message.content}</span>
+          <span className="whitespace-pre-wrap text-sm text-[var(--mu-text-hi)]">{renderContent(message.content)}</span>
         ) : message.streaming ? (
           <span className="mu-blink text-xs text-[var(--mu-text-lo)]">识别中…</span>
         ) : null}
@@ -201,7 +202,7 @@ export function VoiceMessageBody({ message }: { message: ChatMessage }): ReactNo
       </div>
 
       {message.content ? (
-        <div className="mt-2 whitespace-pre-wrap text-xs text-[var(--mu-text-lo)]">{message.content}</div>
+        <div className="mt-2 whitespace-pre-wrap text-xs text-[var(--mu-text-lo)]">{renderContent(message.content)}</div>
       ) : null}
     </div>
   );
@@ -209,7 +210,7 @@ export function VoiceMessageBody({ message }: { message: ChatMessage }): ReactNo
 
 /** agents — sub-agent progress card (kept for the shared flow; monitors live in messages). */
 export function AgentsMessageBody({ message }: { message: ChatMessage }): ReactNode {
-  return shell(<span className="whitespace-pre-wrap">{message.content || fallbackText(message)}</span>);
+  return shell(<span className="whitespace-pre-wrap">{message.content ? renderContent(message.content) : fallbackText(message)}</span>);
 }
 
 /** Reserved — settings is managed in the admin panel; an opaque content fallback. */