diff --git a/package.json b/package.json
index 779e1db90..7f0816038 100644
--- a/package.json
+++ b/package.json
@@ -107,7 +107,8 @@
     "test:danmuku-types-package": "node refactor/scripts/danmuku-package-types.mjs",
     "test:danmuku-mask-types-package": "node refactor/scripts/danmuku-mask-package-types.mjs",
     "test:auto-thumbnail-types": "node --test refactor/scripts/auto-thumbnail-types.test.mjs",
-    "test:auto-thumbnail-types-package": "node refactor/scripts/auto-thumbnail-package-types.mjs"
+    "test:auto-thumbnail-types-package": "node refactor/scripts/auto-thumbnail-package-types.mjs",
+    "probe:auto-thumbnail-rendering": "node refactor/scripts/auto-thumbnail-rendering-probe.mjs"
   },
   "browserslist": "last 1 Chrome version",
   "devDependencies": {
diff --git a/packages/artplayer-plugin-auto-thumbnail/ARCHITECTURE.md b/packages/artplayer-plugin-auto-thumbnail/ARCHITECTURE.md
index 3e54cbaf6..4501e06f6 100644
--- a/packages/artplayer-plugin-auto-thumbnail/ARCHITECTURE.md
+++ b/packages/artplayer-plugin-auto-thumbnail/ARCHITECTURE.md
@@ -139,6 +139,17 @@ close this risk based on the later-cell assertions or replace it with a nonblack
 test; legitimate black frames have opaque pixels. Frame timing, additional
 reentry/cleanup boundaries and resource budgets still need the remaining task03 work.
 
+`yarn probe:auto-thumbnail-rendering` captures an isolated diagnostic matrix from
+the current built ESM and the frozen timeline media. It compares intrinsic-size
+hidden/transparent/clipped/visible elements with current readiness, a readyState
+gate, and waiting for the first loadeddata event. The captured Windows WebKit
+profiles all miss the unique first frame; the Chromium/Firefox controls retain it.
+Seek records distinguish an already-ready element from a delivered loadeddata
+event. A zero getVideoPlaybackQuality().totalVideoFrames is also observed in the
+correct Firefox control, so it is not a portable frame-readiness gate. The command
+reports observations, not a passing acceptance suite, and never edits production
+bundles. See refactor's rendering-readiness record before repeating these options.
+
 The frozen eight-second timeline has one unique purple first frame followed by
 red, black, blue and yellow sections. Its command and fingerprint are in
 `refactor/baselines/auto-thumbnail-timeline-media.json`. Reproduce into a new
diff --git a/refactor/baselines/auto-thumbnail-rendering-readiness.json b/refactor/baselines/auto-thumbnail-rendering-readiness.json
new file mode 100644
index 000000000..53042955f
--- /dev/null
+++ b/refactor/baselines/auto-thumbnail-rendering-readiness.json
@@ -0,0 +1,2715 @@
+{
+  "task": "PKG-AUTO-THUMB-03",
+  "base": "f30c701d88b3c5210b7fa6ddb024b55eeeaf8206",
+  "outcome": "diagnostic-captured-fix-not-found",
+  "reportFile": "refactor/.cache/auto-thumbnail-rendering-l4FCqe/report.json",
+  "reportSha256": "a73f4f1e1774378f3d879b88cf0a0b6408372ccabb3acd5a9f9d9ae7ab652b0e",
+  "capturedAt": "2026-09-13T20:43:29.037Z",
+  "environment": {
+    "node": "v24.21.0",
+    "platform": "win32",
+    "arch": "x64"
+  },
+  "summary": {
+    "webkitProfiles": 12,
+    "webkitCorrectFirstFrame": 0,
+    "chromiumControls": 1,
+    "firefoxControls": 1,
+    "correctControls": 2,
+    "allCompleted": true,
+    "productionChanged": false
+  },
+  "inputs": [
+    {
+      "file": "refactor/scripts/auto-thumbnail-rendering-probe.mjs",
+      "sha256": "cc94cd34582d5ac7ee734b0ec93e3d9328d9b60c510a81e5b6ed6f3d1eac067d"
+    },
+    {
+      "file": "packages/artplayer-plugin-auto-thumbnail/dist/artplayer-plugin-auto-thumbnail.mjs",
+      "sha256": "6080dd90bde239515646899bdd8e71d17de24119523e4883025fbf39b1a6a302"
+    },
+    {
+      "file": "test/browser/media/auto-thumbnail-timeline.mp4",
+      "sha256": "10370156cffada462d3ea00aae0caadd62752369cd6538cc55248b3ddd7bf994"
+    },
+    {
+      "file": "refactor/baselines/auto-thumbnail-timeline-media.json",
+      "sha256": "1bee7645fbdb707679af7b4f8fb9df6e1cd064374d8d16acac1e5b1351725c7d"
+    }
+  ],
+  "supplementary": [
+    {
+      "file": "refactor/.cache/auto-thumbnail-render-path-probe.json",
+      "sha256": "815a28c5fde5aff4d8e4d2caa2bce2887e46edf72d7087c3798b4f3cadf1ddc6",
+      "authority": "Intermediate diagnostic; final guarded instrumentation is in reportFile"
+    },
+    {
+      "file": "refactor/.cache/auto-thumbnail-loaded-event-probe.json",
+      "sha256": "e845366a2ed40abdfa95807502371202ad988bb5a1fa55fde23d0e1c58f1c6b9",
+      "authority": "Intermediate diagnostic; final guarded instrumentation is in reportFile"
+    },
+    {
+      "file": "refactor/.cache/auto-thumbnail-rendering-vdw14M/report.json",
+      "sha256": "5c3f83b88c3bc0474219e4b51abf1734c3f87d6ffd391d7701f2a46721be66d7",
+      "authority": "Intermediate diagnostic; final guarded instrumentation is in reportFile"
+    }
+  ],
+  "logs": [
+    {
+      "file": "refactor/.cache/auto-thumb-rendering-verified.log",
+      "sha256": "f35655c5d6c48405de6a9fc2f4b758d8ba50990c50e27d32febca7f3b8b07326"
+    },
+    {
+      "file": "refactor/.cache/auto-thumb-rendering-lint-final.log",
+      "sha256": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+    }
+  ],
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+      ],
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+        },
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+  ],
+  "limitations": [
+    "Diagnostic command success is not pixel acceptance.",
+    "No CSS/readiness/counter workaround is adopted.",
+    "Captured Windows WebKit behavior is not proof about all Safari versions or physical devices.",
+    "API/core integrations and complete historical type consumers remain separate tasks."
+  ]
+}
diff --git a/refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md b/refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md
new file mode 100644
index 000000000..2224bdecf
--- /dev/null
+++ b/refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md
@@ -0,0 +1,55 @@
+# PKG-AUTO-THUMB-03 渲染与首帧等待对照
+
+状态仍为 doing。这是排除候选原因的检查点，没有修改生产抽帧算法，没有将
+AUTO-THUMB-PIXEL-01 或包迁移标为完成。起点为
+`f30c701d88b3c5210b7fa6ddb024b55eeeaf8206`。
+
+已有 opacity 探针同时把 video 缩成 1px，不能单独回答完整尺寸隐藏方式的影响。
+本次保持实际 320×180 媒体尺寸，分别使用 visibility:hidden、opacity:0、
+clip-path:inset(50%)、完全可见元素，保留原始首帧时间 0 和渐进编码流程。
+运行输入是正式 ESM 的内存副本，改变 CSS 与等待条件只发生在诊断页面中。
+
+第一轮只把无帧回调分支也改为检查 readyState>=2。事件证据显示 metadata
+交付时往往已经是 readyState=4，因此这并不等于真正等到了 loadeddata 事件。
+第二轮明确让第一帧等待 loadeddata，并记录每次 seek 前累计交付的事件数；
+后续帧沿用正常流程。最终脚本同时保留 current、ready-state、loaded-event
+三种策略，避免后续 AI 把不同的等待语义混为一谈。
+
+## 观察与下一步影响
+
+- Windows WebKit 26.6 的 12 种组合均完成五次更新，但没有一组取得时间 0
+  应有的唯一紫色帧。初次 draw 可能是透明像素，也可能已是后续红色；全可见
+  元素也失败。因此不能靠“非黑/不透明”判断已经抽到正确首帧。
+- 四个 loaded-event 变体第一次 seek 前均已交付一次 loadeddata，仍不准确；
+  它们实际执行了事件等待，不是仅根据 readyState 推测已等待。
+- Chromium 153.0.8010.12 与 Firefox 155.0 的当前代码对照均取得唯一紫色首帧；
+  后续颜色与正常黑色内容也被保留。它们具有原生帧呈现回调，WebKit 此环境没有。
+- Firefox 对照画面正确时 totalVideoFrames 仍为 0；Windows WebKit 也为 0。
+  不能将该计数 >0 作为跨浏览器 fallback 的完成条件，否则会卡住正常提取。
+- 三个 WebKit 组合在请求 1.6 秒后又交付了约 0.002 秒的旧 seeked，触发已有
+  同目标重试，最终仍只产生五次 draw。记录保留这六次 seek，不能把采样数五
+  误当作原生事件和重试数也必须为五；这也不解决首帧内容错误。
+- 本次没有实现这些未经验证的 CSS/事件/计数修复；也没有删除或放宽现有像素
+  检查。后续需要从当前 WebKit 媒体路径或实际支持设备取得更直接证据，不能
+  继续把上述样式/readyState/loadeddata 的简单变体当作尚未尝试的新方案。
+
+具体结果、事件次序、代码与媒体指纹见
+[验证记录](../baselines/auto-thumbnail-rendering-readiness.json)。首轮/事件补充
+缓存报告也保留指纹，最终十四组来自提交脚本，而不是用文字推测先前探针结果。
+这些是一次版本固定的观测，不能外推为所有 WebKit/Safari 版本或物理设备缺陷。
+
+## 重跑与维护
+
+```sh
+yarn build artplayer-plugin-auto-thumbnail
+yarn probe:auto-thumbnail-rendering
+```
+
+第二条只读取产物和固定媒体，启动 loopback 临时端口，依次启动三个测试浏览器，
+输出到新的 `.cache/auto-thumbnail-rendering-*`。脚本检查精确可替换代码位置，
+记录各变体 hash，结束时检查源产物没有变化。它是诊断采集命令，不加入默认
+通过测试列表，也不把成功退出解释为像素已通过。八秒是探针采集上限，不是
+新生产超时。使用现有 Playwright 依赖，没有增加或升级依赖、版本或发布产物。
+
+本项只有诊断脚本、入口、说明和证据变更；不声称修复所有旧类型/首帧问题。
+回退该检查点会移除诊断入口和记录，不影响 07/08/09 的生产修复。
diff --git a/refactor/plan.md b/refactor/plan.md
index 223e67670..3671aff68 100644
--- a/refactor/plan.md
+++ b/refactor/plan.md
@@ -517,7 +517,7 @@
 - PKG-AUDIO-05: [记录](changes/2026-09-12-PKG-AUDIO-05-combinations.md) [记录](baselines/audio-combinations-first.json) [记录](baselines/audio-combinations-checkpoint.json) [记录](audio-validation.md)
 - PKG-AUTO-THUMB-01: [记录](baselines/auto-thumbnail-release.json) [记录](baselines/auto-thumbnail-contract.md) [记录](changes/2026-09-13-PKG-AUTO-THUMB-01-contract.md) [记录](baselines/auto-thumbnail-contract-validation.json)
 - PKG-AUTO-THUMB-02: [记录](baselines/auto-thumbnail-failures.md) [记录](baselines/auto-thumbnail-failures-validation.json) [记录](changes/2026-09-13-PKG-AUTO-THUMB-02-failures.md)
-- PKG-AUTO-THUMB-03: [记录](changes/2026-09-13-PKG-AUTO-THUMB-03-lifecycle-checkpoint.md) [记录](baselines/auto-thumbnail-lifecycle-checkpoint.json) [记录](changes/2026-09-13-PKG-AUTO-THUMB-03-hidden-renderer.md) [记录](baselines/auto-thumbnail-hidden-renderer.json) [记录](baselines/auto-thumbnail-timeline-media.json) [记录](changes/2026-09-13-PKG-AUTO-THUMB-03-frame-presentation.md) [记录](baselines/auto-thumbnail-frame-presentation.json)
+- PKG-AUTO-THUMB-03: [记录](changes/2026-09-13-PKG-AUTO-THUMB-03-lifecycle-checkpoint.md) [记录](baselines/auto-thumbnail-lifecycle-checkpoint.json) [记录](changes/2026-09-13-PKG-AUTO-THUMB-03-hidden-renderer.md) [记录](baselines/auto-thumbnail-hidden-renderer.json) [记录](baselines/auto-thumbnail-timeline-media.json) [记录](changes/2026-09-13-PKG-AUTO-THUMB-03-frame-presentation.md) [记录](baselines/auto-thumbnail-frame-presentation.json) [记录](changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md) [记录](baselines/auto-thumbnail-rendering-readiness.json)
 - PKG-VTT-THUMB-01: [记录](baselines/vtt-thumbnail-release.json) [记录](baselines/vtt-thumbnail-contract.md) [记录](changes/2026-09-13-PKG-VTT-THUMB-01-contract.md)
 - PKG-VTT-THUMB-02: [记录](baselines/vtt-thumbnail-failures.json) [记录](changes/2026-09-13-PKG-VTT-THUMB-02-failures.md)
 - PKG-VTT-THUMB-03: [记录](changes/2026-09-13-PKG-VTT-THUMB-03-resources.md) [记录](baselines/vtt-thumbnail-resources.json) [记录](changes/2026-09-13-PKG-VTT-THUMB-03-parser.md) [记录](baselines/vtt-thumbnail-parser.json)
diff --git a/refactor/progress.md b/refactor/progress.md
index cc91a0b51..1e508a8fc 100644
--- a/refactor/progress.md
+++ b/refactor/progress.md
@@ -1,5 +1,20 @@
 # 进度与证据
 
+## PKG-AUTO-THUMB-03 渲染/等待诊断检查点（仍 doing）
+
+新增可重跑的 `yarn probe:auto-thumbnail-rendering`，用固定实际 ESM/时间轴媒体
+对照真实尺寸下四种可见性样式及 current/readyState/loadeddata 事件三种策略。
+最终 Windows WebKit 12 组均未取得唯一紫色首帧；Chromium/Firefox 两个对照正常。
+首个 loadeddata 的交付计数被直接记录，避免将 readyState>=2 误称为已等待事件。
+正确 Firefox 帧的 totalVideoFrames 仍为 0，不能用该计数 >0 构造通用等待条件。
+另外捕获三组旧 seeked 导致的同目标重试，保留全部事件，不把它算作额外采样。
+生产源码、dist 和普通像素断言均未改变；没有采用未通过验证的 CSS/等待修复。
+见[诊断记录](changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md)与
+[证据](baselines/auto-thumbnail-rendering-readiness.json)。脚本/lint/工具链及计划
+检查通过只说明诊断可运行，不代表首帧通过。PIXEL-01 和 03 保持未完成，计划
+仍为 237 项：160 done、15 doing、62 todo。后续不再重复这些已否定的简单策略，
+继续定位当前媒体路径和补齐独立的历史消费验证；VAST 默认初始化选择仍待答复。
+
 ## PKG-AUTO-THUMB-09 历史 default 调用兼容完成
 
 通过同一函数上的 default 自引用补齐 1.0.1 的 JavaScript 调用，继续支持 1.1.0
diff --git a/refactor/risks.json b/refactor/risks.json
index 19cae8fb1..b4ae00bfa 100644
--- a/refactor/risks.json
+++ b/refactor/risks.json
@@ -4166,9 +4166,11 @@
         "refactor/baselines/auto-thumbnail-hidden-renderer.json",
         "refactor/baselines/auto-thumbnail-timeline-media.json",
         "test/auto-thumbnail-frames.test.js",
-        "refactor/baselines/auto-thumbnail-frame-presentation.json"
+        "refactor/baselines/auto-thumbnail-frame-presentation.json",
+        "refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md",
+        "refactor/baselines/auto-thumbnail-rendering-readiness.json"
       ],
-      "compatibleResolution": "Establish actual decoded-frame readiness for the existing timeline/grid and preserve silent independent extraction; do not waive colored pixel checks as unsupported media.",
+      "compatibleResolution": "Establish actual decoded-frame readiness for the existing timeline/grid and preserve silent independent extraction; do not waive colored pixel checks as unsupported media. Intrinsic-size hidden/opacity/clip/visible rendering crossed with current/readyState/first-loadeddata-event strategies still misses the unique first frame in all 12 Windows WebKit profiles. Correct Firefox frames retain totalVideoFrames=0, so that counter cannot be a portable readiness gate. Do not reintroduce these unvalidated workarounds.",
       "closureCriteria": "Candidate source and artifacts generate usable sampled pixels on native browser controls with lifecycle checks; supported Safari and core combinations remain explicit final gates.",
       "workspaceState": "The frames module now waits for native presentation and seek completion on capable browsers. Chromium/Firefox source/main/legacy assert all five cells including first purple frame, second red cell, legitimate black and presentation times. Callback-less Windows WebKit first two cells remain diagnostic, later cells asserted; physical Safari/core combinations remain open. 84 native lifecycle/pixel cases passed with explicit held native-frame vs Blob-fallback paths; 19 new Node cases fail 17 ways on prior checkpoint and all 52 current cases pass per candidate. Risk and task03 remain open."
     },
diff --git a/refactor/scripts/auto-thumbnail-rendering-probe.mjs b/refactor/scripts/auto-thumbnail-rendering-probe.mjs
new file mode 100644
index 000000000..14cf87996
--- /dev/null
+++ b/refactor/scripts/auto-thumbnail-rendering-probe.mjs
@@ -0,0 +1,135 @@
+import assert from 'node:assert/strict'
+import { createHash } from 'node:crypto'
+import fs from 'node:fs'
+import http from 'node:http'
+import process from 'node:process'
+import { chromium, firefox, webkit } from '@playwright/test'
+
+const bundle = fs.readFileSync('packages/artplayer-plugin-auto-thumbnail/dist/artplayer-plugin-auto-thumbnail.mjs', 'utf8')
+const bytes = fs.readFileSync('test/browser/media/auto-thumbnail-timeline.mp4')
+assert.equal(process.version.slice(1), fs.readFileSync('.node-version', 'utf8').trim())
+assert.equal(process.env.npm_config_user_agent?.split(' ')[0], 'yarn/1.22.22', 'Use yarn probe:auto-thumbnail-rendering')
+const output = fs.mkdtempSync('refactor/.cache/auto-thumbnail-rendering-')
+console.log(`Rendering diagnostics: ${output}`)
+const fingerprint = data => createHash('sha256').update(data).digest('hex')
+assert.equal(fingerprint(bytes), JSON.parse(fs.readFileSync('refactor/baselines/auto-thumbnail-timeline-media.json')).file.sha256, 'The unique-frame diagnostic requires the frozen timeline fixture')
+assert(bundle.includes('const ready = !presentedFrames || video.readyState >= 2;'))
+assert(bundle.includes('visibility:hidden;'))
+assert.equal(bundle.match(/let pending;/g)?.length, 1)
+assert.equal(bundle.match(/video.currentTime = target;/g)?.length, 1)
+const server = http.createServer((request, response) => {
+  if (request.url !== '/video.mp4') {
+    response.writeHead(200, { 'Content-Type': 'text/html' })
+    response.end('<!doctype html><title>Frame rendering probe</title>')
+    return
+  }
+  const match = /^bytes=(\d+)-(\d*)$/.exec(request.headers.range || '')
+  const start = match ? Number(match[1]) : 0
+  const end = match?.[2] ? Math.min(Number(match[2]), bytes.length - 1) : bytes.length - 1
+  response.writeHead(match ? 206 : 200, { 'Content-Type': 'video/mp4', 'Content-Length': end - start + 1, 'Accept-Ranges': 'bytes', ...(match ? { 'Content-Range': `bytes ${start}-${end}/${bytes.length}` } : {}) })
+  response.end(bytes.subarray(start, end + 1))
+})
+await new Promise(resolve => server.listen(0, '127.0.0.1', resolve))
+const styles = { hidden: 'visibility:hidden;', opacity: 'visibility:visible;opacity:0;', clip: 'visibility:visible;clip-path:inset(50%);', visible: 'visibility:visible;' }
+const results = []
+function purple([red, green, blue, alpha]) {
+  return alpha === 255 && Math.min(red, blue) > 100 && Math.abs(red - blue) < 30 && green < 40
+}
+try {
+  for (const [engineName, engine] of Object.entries({ webkit, chromium, firefox })) {
+    const browser = await engine.launch()
+    try {
+      const variants = engineName === 'webkit'
+        ? Object.entries(styles).flatMap(([style, css]) => ['current', 'ready-state', 'loaded-event'].map(readiness => ({ style, css, readiness })))
+        : [{ style: 'hidden', css: styles.hidden, readiness: 'current' }]
+      for (const variant of variants) {
+        const page = await browser.newPage()
+        await page.goto(`http://127.0.0.1:${server.address().port}`)
+        let code = bundle.replace('visibility:hidden;', variant.css)
+        if (variant.readiness === 'ready-state')
+          code = code.replace('const ready = !presentedFrames || video.readyState >= 2;', 'const ready = video.readyState >= 2;')
+        if (variant.readiness === 'loaded-event')
+          code = code.replace('let pending;', 'let pending; let firstFrame = true;').replace('const ready = !presentedFrames || video.readyState >= 2;', 'const ready = !firstFrame; firstFrame = false;')
+        code = code.replace('video.currentTime = target;', '{ window.__thumbnailSeeks.push({target, loadedData: window.__thumbnailData, readyState: video.readyState}); video.currentTime = target; }')
+        const result = await page.evaluate(async (code) => {
+          const draws = []
+          const events = []
+          const updates = []
+          const warnings = []
+          const videos = []
+          window.__thumbnailData = 0
+          window.__thumbnailSeeks = []
+          const create = document.createElement.bind(document)
+          const draw = CanvasRenderingContext2D.prototype.drawImage
+          const originalWarn = console.warn
+          console.warn = (...args) => warnings.push(args.map(String))
+          document.createElement = (...args) => {
+            const element = create(...args)
+            if (args[0] === 'video') {
+              videos.push(element)
+              element.addEventListener('loadeddata', () => window.__thumbnailData++)
+              for (const name of ['loadedmetadata', 'loadeddata', 'canplay', 'seeked', 'playing']) element.addEventListener(name, () => events.push({ name, time: element.currentTime, readyState: element.readyState, decoded: element.webkitDecodedFrameCount, total: element.getVideoPlaybackQuality?.().totalVideoFrames }))
+            }
+            return element
+          }
+          CanvasRenderingContext2D.prototype.drawImage = function (source, ...args) {
+            const result = draw.call(this, source, ...args)
+            if (source instanceof HTMLVideoElement) {
+              const [x, y, width, height] = args
+              draws.push({ time: source.currentTime, rgba: [...this.getImageData(x + Math.floor(width / 2), y + Math.floor(height / 2), 1, 1).data], readyState: source.readyState, decoded: source.webkitDecodedFrameCount, total: source.getVideoPlaybackQuality?.().totalVideoFrames, box: { width: source.getBoundingClientRect().width, height: source.getBoundingClientRect().height } })
+            }
+            return result
+          }
+          const listeners = new Map()
+          let finish
+          const done = new Promise(resolve => finish = resolve)
+          const art = {
+            option: { url: '/video.mp4' },
+            on(name, fn) {
+              if (!listeners.has(name))
+                listeners.set(name, new Set())
+              listeners.get(name).add(fn)
+            },
+            off(name, fn) { listeners.get(name)?.delete(fn) },
+            get thumbnails() { return updates.at(-1) },
+            set thumbnails(value) {
+              updates.push(value)
+              if (updates.length === 5)
+                finish('completed')
+            },
+          }
+          const emit = (name) => {
+            for (const fn of [...(listeners.get(name) || [])]) fn()
+          }
+          let timer
+          try {
+            const { default: factory } = await import(`data:text/javascript,${encodeURIComponent(code)}`)
+            await factory({ width: 80, number: 5 })(art)
+            timer = setTimeout(() => finish('timeout'), 8000)
+            emit('video:loadedmetadata')
+            const outcome = await done
+            return { outcome, draws, events, warnings, seeks: window.__thumbnailSeeks, supportsFrames: typeof videos[0]?.requestVideoFrameCallback === 'function' && typeof videos[0]?.cancelVideoFrameCallback === 'function' }
+          }
+          finally {
+            clearTimeout(timer)
+            emit('destroy')
+            document.createElement = create
+            CanvasRenderingContext2D.prototype.drawImage = draw
+            console.warn = originalWarn
+          }
+        }, code)
+        const firstFrameMatches = result.draws[0] ? purple(result.draws[0].rgba) : false
+        const entry = { engine: engineName, browser: browser.version(), ...variant, codeSha256: fingerprint(code), firstFrameMatches, ...result }
+        results.push(entry)
+        console.log(JSON.stringify({ engine: engineName, ...variant, outcome: result.outcome, firstFrameMatches, seeks: result.seeks, draws: result.draws.map(item => ({ time: item.time, rgba: item.rgba, total: item.total })) }))
+        await page.close()
+      }
+    }
+    finally { await browser.close() }
+  }
+}
+finally {
+  await new Promise(resolve => server.close(resolve))
+  assert.equal(fs.readFileSync('packages/artplayer-plugin-auto-thumbnail/dist/artplayer-plugin-auto-thumbnail.mjs', 'utf8'), bundle)
+  fs.writeFileSync(`${output}/report.json`, `${JSON.stringify({ capturedAt: new Date().toISOString(), environment: { node: process.version, platform: process.platform, arch: process.arch }, sourceSha256: fingerprint(bundle), mediaSha256: fingerprint(bytes), results, scope: 'Diagnostic capture, not acceptance. Four intrinsic-size rendering modes and three first-frame readiness strategies are compared in WebKit on the recorded host. Chromium/Firefox current-code controls retain native presentation callbacks. No production file is changed; missing or incorrect pixels remain explicit.' }, null, 2)}\n`)
+}
diff --git a/refactor/tasks.json b/refactor/tasks.json
index 0ecc9c19c..724d2b78d 100644
--- a/refactor/tasks.json
+++ b/refactor/tasks.json
@@ -1797,7 +1797,9 @@
         "baselines/auto-thumbnail-hidden-renderer.json",
         "baselines/auto-thumbnail-timeline-media.json",
         "changes/2026-09-13-PKG-AUTO-THUMB-03-frame-presentation.md",
-        "baselines/auto-thumbnail-frame-presentation.json"
+        "baselines/auto-thumbnail-frame-presentation.json",
+        "changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md",
+        "baselines/auto-thumbnail-rendering-readiness.json"
       ]
     },
     {
diff --git a/test/README.md b/test/README.md
index d4ca0a5a6..501353b46 100644
--- a/test/README.md
+++ b/test/README.md
@@ -15,6 +15,13 @@ runtime types describe the alias without changing the historical root declaratio
 This does not decode video or close all older type-shape, native pixel, or device
 acceptance gaps. Candidate entry types use the same runtime files.
 
+`yarn probe:auto-thumbnail-rendering` is an optional diagnosis command, separate
+from passing test suites. It runs four intrinsic-size rendering modes and three
+readiness strategies in Windows WebKit, plus Chromium/Firefox controls. It records
+raw draw pixels, seek/event ordering, frame counters and exact code/media hashes
+in a new cache directory. Completion of the command does not imply correct pixels:
+the current WebKit first-frame discrepancy remains an open release/refactor risk.
+
 `yarn test:danmuku-mask` runs candidate run cancellation/resource ownership plus
 frozen historical defects and public contracts. Candidate tests also run in
 `test:unit`; their controlled SDK, RAF and canvas hosts do not prove native model