feat: 缓存命中率有来源了（assistant/chunk 的 usage 事件）+ DSH 启动自动拉起浮窗

挖到真源：事件流里 assistant/chunk 带 chunk.type='usage'
  {inputTokens,outputTokens,cacheReadTokens,reasoningTokens}
从此算出真实指标（不再依赖 tokenMeter 的估算）：
  缓存命中率 = cacheRead/(input+cacheRead)     实测 0.9976（与 App 状态栏 99% 一致）
  总量       = output + input + cacheRead      实测 88.99M
  tok/s      = outputTokens/该步耗时            实测 37.3
  上下文占用 = 最后一步的 input+cacheRead / 窗口（不是历史累加）  实测 56.3%
插件与镜像桥两侧都接上了；镜像桥改为跟随插件认定的当前会话。

另：autoOpen（默认开）——DSH 启动后 1.5s 若浮窗没在跑就自动拉起（用户选定）。

tools/mirror-bridge.mjs

@@ -87,6 +87,13 @@ function rowsFromLog(text) {
   let streamStart = 0
   let streamChars = 0
   let lastChunkAt = 0
+  let outTokens = 0
+  let inTokens = 0
+  let cacheRead = 0
+  let stepStart = 0
+  let decodeMs = 0
+  let lastTps = null
+  let lastPromptTokens = 0 // 最后一步的输入(=未缓存+命中缓存)：这才是"当前上下文占用"
   const est = (chars) => Math.round(chars / 3.2) // 中英混排的粗略 token 估算
 
   for (const line of text.split('\n')) {
@@ -97,7 +104,7 @@ function rowsFromLog(text) {
     const d = e?.data || e || {}
     const t = e?.time || 0
     if (type === 'turn/start') turns++
-    else if (type === 'step/start') steps++
+    else if (type === 'step/start') { steps++; stepStart = t || Date.now() }
     else if (type === 'request/context' && d.contextWindow) contextWindow = d.contextWindow
     else if (type === 'session/title' && d.title) titles.set('title', String(d.title))
     else if (type === 'user/message') {
@@ -110,6 +117,17 @@ function rowsFromLog(text) {
     } else if (type === 'assistant/chunk') {
       const c = d.chunk || {}
       const kind = String(c.type || '')
+      if (kind === 'usage' && c.usage) {
+        // 真实用量：{inputTokens,outputTokens,cacheReadTokens,reasoningTokens}
+        const u = c.usage
+        inTokens += u.inputTokens || 0
+        cacheRead += u.cacheReadTokens || 0
+        outTokens += u.outputTokens || 0
+        lastPromptTokens = (u.inputTokens || 0) + (u.cacheReadTokens || 0)
+        const ms = stepStart ? (t || Date.now()) - stepStart : 0
+        if (u.outputTokens && ms > 0) { decodeMs += ms; lastTps = u.outputTokens / (ms / 1000) }
+        continue
+      }
       const piece = c.text ?? c.delta ?? (kind.includes('text') ? c.content : '')
       if (piece) {
         const now = t || Date.now()
@@ -129,16 +147,20 @@ function rowsFromLog(text) {
   }
   for (const r of rows) delete r.streaming
   const streaming = lastChunkAt && Date.now() - lastChunkAt < 8000
-  const tps = streaming && streamStart ? est(streamChars) / Math.max(0.5, (lastChunkAt - streamStart) / 1000) : null
+  // tok/s：优先用真实 outputTokens/步耗时；否则退化成"流式字符估算"
+  const tps = lastTps ?? (streaming && streamStart ? est(streamChars) / Math.max(0.5, (lastChunkAt - streamStart) / 1000) : null)
+  const promptTokens = inTokens + cacheRead
+  const realUsage = promptTokens + outTokens > 0
   return {
     rows, titles, turns, steps, streaming,
     metrics: {
       turns,
       steps,
       tps,
-      tokens: outChars ? est(outChars + userChars) : null,
-      cacheHit: null,
-      contextUsed: contextWindow ? Math.min(1, est(userChars + outChars) / contextWindow) : null,
+      // 有真实用量就用真实值；否则退化成字符估算（界面会带 ≈）
+      tokens: realUsage ? outTokens + promptTokens : (outChars ? est(outChars + userChars) : null),
+      cacheHit: promptTokens > 0 ? cacheRead / promptTokens : null,
+      contextUsed: contextWindow ? Math.min(1, (realUsage ? lastPromptTokens : est(userChars + outChars)) / contextWindow) : null,
     },
   }
 }
@@ -164,9 +186,16 @@ function buildSnapshot() {
     })
   }
 
-  // 当前会话：watch.json 指定优先，否则"日志最新"（真正在跑的那个）
+  // 当前会话：watch.json 指定 > 插件自己认定的当前会话 > 日志最新
   let active = null
   if (watch?.sessionId) active = entries.find((e) => e.id === watch.sessionId || e.id.replace(/^session-/, '') === watch.sessionId) || null
+  if (!active) {
+    // 插件写的 snapshot.json 带 sessionId：跟它走，指标缺口才能对上同一个会话
+    const plug = readJson(SNAPSHOT)
+    if (plug?.sessionId && !plug.source) {
+      active = entries.find((e) => e.id === plug.sessionId || e.id.replace(/^session-/, '') === plug.sessionId) || null
+    }
+  }
   if (!active) active = entries.sort((a, b) => b.mtime - a.mtime)[0] || null
   if (!active) return null