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/lib/parseContent.ts

@@ -0,0 +1,66 @@
+// Structured parser for persona action/narration XML tags (design/07 §1).
+// A single message `content` may mix plain text with `<action>…</action>` and
+// `<narration>…</narration>`; this splits it into an ordered parts array so the
+// UI can render inline (grey italic) while the structured data stays available
+// for downstream feeds (mind-map / state) via `summarizeContent`.
+
+export type ContentPartType = "text" | "action" | "narration";
+
+export interface ContentPart {
+  type: ContentPartType;
+  text: string;
+}
+
+/** Matches a well-formed `<action>…</action>` or `<narration>…</narration>`.
+ *  Non-greedy body (`[\s\S]*?`) stops at the first matching close tag, so the
+ *  tags can span multiple lines. Unclosed or malformed tags simply do not match
+ *  and fall through as plain text — a literal `<` in the body never breaks. */
+const TAG_RE = /<\s*(action|narration)\s*>([\s\S]*?)<\/\s*\1\s*>/g;
+
+/**
+ * Split `content` into an ordered parts array preserving tag position.
+ * Pure text with no tags yields a single `{type:"text"}` part.
+ */
+export function parseContent(content: string): ContentPart[] {
+  const parts: ContentPart[] = [];
+  let lastIndex = 0;
+
+  for (const m of content.matchAll(TAG_RE)) {
+    const index = m.index ?? content.length;
+    const before = content.slice(lastIndex, index);
+    if (before) parts.push({ type: "text", text: before });
+    parts.push({ type: m[1] === "action" ? "action" : "narration", text: m[2] });
+    lastIndex = index + m[0].length;
+  }
+
+  const tail = content.slice(lastIndex);
+  if (tail) parts.push({ type: "text", text: tail });
+  if (parts.length === 0) parts.push({ type: "text", text: content });
+
+  return parts;
+}
+
+/** One extracted tag value. */
+export interface ContentTagItem {
+  text: string;
+}
+
+/** Flat summary derived from the parts: the plain body string plus the collected
+ *  action / narration values. Useful for mind-map / state feeds that want the
+ *  structured payload rather than the inline render. */
+export interface ContentSummary {
+  text: string;
+  actions: ContentTagItem[];
+  narrations: ContentTagItem[];
+}
+
+/** Collapse a message into `{text, actions, narrations}`. */
+export function summarizeContent(content: string): ContentSummary {
+  const summary: ContentSummary = { text: "", actions: [], narrations: [] };
+  for (const part of parseContent(content)) {
+    if (part.type === "text") summary.text += part.text;
+    else if (part.type === "action") summary.actions.push({ text: part.text });
+    else summary.narrations.push({ text: part.text });
+  }
+  return summary;
+}

frontend/web/src/lib/renderContent.tsx

@@ -0,0 +1,19 @@
+import type { ReactNode } from "react";
+import { parseContent, type ContentPart } from "../lib/parseContent";
+
+/** Render a message body into inline parts: plain text as-is, while
+ *  `<action>` / `<narration>` become muted italic spans (Miuix `--mu-text-lo`).
+ *  Whitespace is preserved by the caller's `whitespace-pre-wrap` container — the
+ *  returned nodes are just the segments dropped into it in order. */
+export function renderContent(content: string): ReactNode[] {
+  return parseContent(content).map((part, i) => renderPart(part, i));
+}
+
+function renderPart(part: ContentPart, key: number): ReactNode {
+  if (part.type === "text") return <span key={key}>{part.text}</span>;
+  return (
+    <span key={key} className="italic text-[var(--mu-text-lo)]">
+      {part.text}
+    </span>
+  );
+}