diff --git a/package.json b/package.json
index 38c7a6921..7bf94ea9f 100644
--- a/package.json
+++ b/package.json
@@ -132,7 +132,8 @@
     "test:scaffold": "node --test test/plugin-scaffold.test.js",
     "typecheck:library": "node node_modules/typescript/bin/tsc -p scripts/tsconfig.library.json --noEmit",
     "test:library": "node --test refactor/scripts/build.test.mjs test/library-build.test.js test/performance-report.test.js test/plugin-scaffold.test.js test/dev-server.test.js",
-    "test:dev-server": "node --test test/dev-server.test.js"
+    "test:dev-server": "node --test test/dev-server.test.js",
+    "probe:auto-thumbnail-native": "node refactor/scripts/auto-thumbnail-native-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 ac4179582..2f5a3a066 100644
--- a/packages/artplayer-plugin-auto-thumbnail/ARCHITECTURE.md
+++ b/packages/artplayer-plugin-auto-thumbnail/ARCHITECTURE.md
@@ -158,6 +158,26 @@ These variants still fail the unique-first-frame check on the recorded Windows
 WebKit host. They are diagnostic page-owned callbacks, not production fixes or
 cancellation code. See refactor's first-seek checkpoint before repeating them.
 
+`yarn probe:auto-thumbnail-native` removes ArtPlayer and this plugin entirely.
+It serves the frozen timeline with the owned dev server, plus a diagnostic H.264
+transcode with B frames disabled, and samples native video/canvas in hidden paused,
+visible paused and hidden play-then-immediately-pause modes. It verifies both
+files' first purple pixel with FFmpeg before browser capture. FFmpeg/FFprobe must
+be installed (optional FFMPEG/FFPROBE executable paths); exact version, arguments,
+media hashes, browser versions, events and all31 samples are recorded in an ignored
+cache directory. It does not replace the acceptance fixture or add an npm dependency.
+
+The Windows18-case capture still misses the first purple frame in all6 WebKit
+cases without any plugin code; Chromium/Firefox controls recover it. The visible
+original video can remain at currentTime0 while canvas exposes the later red
+frame. This narrows investigation to the native surface on that tested host, but
+does not certify all Safari versions or excuse plugin pixel gates. Exploratory
+rate0/slow-rate, fastSeek, tiny first-seek offsets and pre-load/metadata layout or
+paint waits did not fix it either. The next useful pixel evidence is the same
+native/candidate case on another supported backend/device or a decoded-frame
+path with explicit timestamps, not another arbitrary wait. See the native-decoder
+checkpoint in refactor; AUTO-THUMB-PIXEL-01 and task03 remain open.
+
 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-native-decoder.json b/refactor/baselines/auto-thumbnail-native-decoder.json
new file mode 100644
index 000000000..b1f1ff886
--- /dev/null
+++ b/refactor/baselines/auto-thumbnail-native-decoder.json
@@ -0,0 +1,1904 @@
+{
+  "task": "PKG-AUTO-THUMB-03",
+  "status": "doing",
+  "baselineCommit": "772d79a67196ff61dc1e90499c275fee936cb942",
+  "outcome": "Native first-frame defect reproduced without plugin; production fix remains unproven",
+  "script": {
+    "file": "refactor/scripts/auto-thumbnail-native-probe.mjs",
+    "sha256": "448c701a8b91ecd352da349ac6afca3ba20e3abc234fe508fbb5289b8d6933cc"
+  },
+  "final": {
+    "report": {
+      "file": "refactor/.cache/auto-thumbnail-native-1n8pV4/report.json",
+      "sha256": "bc686de7b8eac909fc3f28684bc4801ec9ad2c8848cbe0b9d1e05428f48d9192"
+    },
+    "log": {
+      "file": "refactor/.cache/auto-native-probe-final.log",
+      "sha256": "7c6a890751dace746348c545689bcd8341aff6f709c4059877624fa1b7cdb2c9"
+    },
+    "capturedAt": "2026-09-14T03:37:51.659Z",
+    "node": "v24.21.0",
+    "platform": "win32",
+    "ffmpegVersion": "ffmpeg version 2025-11-12-git-6cdd2cbe32-full_build-www.gyan.dev Copyright (c) 2000-2025 the FFmpeg developers",
+    "args": [
+      "-hide_banner",
+      "-loglevel",
+      "error",
+      "-n",
+      "-i",
+      "test/browser/media/auto-thumbnail-timeline.mp4",
+      "-map",
+      "0:v:0",
+      "-an",
+      "-c:v",
+      "libx264",
+      "-pix_fmt",
+      "yuv420p",
+      "-bf",
+      "0",
+      "-g",
+      "30",
+      "-crf",
+      "18",
+      "-movflags",
+      "+faststart",
+      "refactor\\.cache\\auto-thumbnail-native-1n8pV4\\no-b-frames.mp4"
+    ],
+    "media": [
+      {
+        "file": "refactor\\.cache\\auto-thumbnail-native-1n8pV4\\original.mp4",
+        "sha256": "10370156cffada462d3ea00aae0caadd62752369cd6538cc55248b3ddd7bf994",
+        "metadata": {
+          "programs": [],
+          "stream_groups": [],
+          "streams": [
+            {
+              "codec_name": "h264",
+              "profile": "High",
+              "has_b_frames": 2,
+              "time_base": "1/15360",
+              "start_time": "0.000000",
+              "duration": "8.000000"
+            }
+          ]
+        },
+        "ffmpegFirstPixel": [
+          128,
+          0,
+          128,
+          255
+        ]
+      },
+      {
+        "file": "refactor\\.cache\\auto-thumbnail-native-1n8pV4\\no-b-frames.mp4",
+        "sha256": "d08af99bc5021eedd4c32112e3f0b7d08c85bd35da39711362a71a9a9274ce3e",
+        "metadata": {
+          "programs": [],
+          "stream_groups": [],
+          "streams": [
+            {
+              "codec_name": "h264",
+              "profile": "High",
+              "has_b_frames": 0,
+              "time_base": "1/15360",
+              "start_time": "0.000000",
+              "duration": "8.000000"
+            }
+          ]
+        },
+        "ffmpegFirstPixel": [
+          128,
+          0,
+          128,
+          255
+        ]
+      }
+    ],
+    "results": [
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+        "browser": "26.6",
+        "file": "original.mp4",
+        "mode": "paused",
+        "purpleSamples": 0,
+        "mediaError": 0,
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+        "sha256": "41e83c785348abb7b4de1b8a0a2b569880b18302e793ad77fa57d8436a0e9366"
+      },
+      "generator": {
+        "file": "refactor/.cache/auto-layout-probe.mjs",
+        "sha256": "bb48890ad01bf1b98f624381b1f692dd08329c672492d4842867c455f628f981"
+      },
+      "generatedRunner": {
+        "file": "refactor/.cache/auto-layout-generated.mjs",
+        "sha256": "68484ecb8316a61c1037ee246deb61793c3f2f819f811413e1b1d4a4c5edcc16"
+      },
+      "results": [
+        {
+          "engine": "webkit",
+          "browser": "26.6",
+          "variant": "current",
+          "outcome": "completed",
+          "firstFrameMatches": false,
+          "firstDraw": {
+            "time": 0,
+            "rgba": [
+              0,
+              0,
+              0,
+              0
+            ],
+            "readyState": 4,
+            "decoded": 0,
+            "total": 0,
+            "box": {
+              "width": 320,
+              "height": 180
+            }
+          },
+          "codeSha256": "6080dd90bde239515646899bdd8e71d17de24119523e4883025fbf39b1a6a302"
+        },
+        {
+          "engine": "webkit",
+          "browser": "26.6",
+          "variant": "layout-before-src",
+          "outcome": "completed",
+          "firstFrameMatches": false,
+          "firstDraw": {
+            "time": 0,
+            "rgba": [
+              0,
+              0,
+              0,
+              0
+            ],
+            "readyState": 4,
+            "decoded": 0,
+            "total": 0,
+            "box": {
+              "width": 320,
+              "height": 180
+            }
+          },
+          "codeSha256": "808efa8818d5f317a92777ada48d39dfaadb9c6eba63845ff42b606dadfc60c8"
+        },
+        {
+          "engine": "webkit",
+          "browser": "26.6",
+          "variant": "paint-before-src",
+          "outcome": "completed",
+          "firstFrameMatches": false,
+          "firstDraw": {
+            "time": 0.0022993,
+            "rgba": [
+              0,
+              0,
+              0,
+              0
+            ],
+            "readyState": 4,
+            "decoded": 0,
+            "total": 0,
+            "box": {
+              "width": 320,
+              "height": 180
+            }
+          },
+          "codeSha256": "45a48611d5e887f2957a35b4e95ef13ac6d69a5a0a29b64e70accd49a39481e1"
+        },
+        {
+          "engine": "webkit",
+          "browser": "26.6",
+          "variant": "layout-metadata",
+          "outcome": "completed",
+          "firstFrameMatches": false,
+          "firstDraw": {
+            "time": 0.0020653,
+            "rgba": [
+              0,
+              0,
+              0,
+              0
+            ],
+            "readyState": 4,
+            "decoded": 0,
+            "total": 0,
+            "box": {
+              "width": 320,
+              "height": 180
+            }
+          },
+          "codeSha256": "d2277236eaf1eeda7c81e2e60475461b66e584a27c16c8df3533c778e2936472"
+        },
+        {
+          "engine": "webkit",
+          "browser": "26.6",
+          "variant": "paint-metadata",
+          "outcome": "completed",
+          "firstFrameMatches": false,
+          "firstDraw": {
+            "time": 0.0011836,
+            "rgba": [
+              238,
+              14,
+              14,
+              255
+            ],
+            "readyState": 4,
+            "decoded": 0,
+            "total": 0,
+            "box": {
+              "width": 320,
+              "height": 180
+            }
+          },
+          "codeSha256": "86a958c31466f1b361572f64e76ad0706ae7a401802cefee53a3951190a4df5e"
+        },
+        {
+          "engine": "chromium",
+          "browser": "153.0.8010.12",
+          "variant": "current",
+          "outcome": "completed",
+          "firstFrameMatches": true,
+          "firstDraw": {
+            "time": 0,
+            "rgba": [
+              127,
+              0,
+              126,
+              255
+            ],
+            "readyState": 4,
+            "decoded": 4,
+            "total": 4,
+            "box": {
+              "width": 320,
+              "height": 180
+            }
+          },
+          "codeSha256": "6080dd90bde239515646899bdd8e71d17de24119523e4883025fbf39b1a6a302"
+        },
+        {
+          "engine": "chromium",
+          "browser": "153.0.8010.12",
+          "variant": "layout-before-src",
+          "outcome": "completed",
+          "firstFrameMatches": true,
+          "firstDraw": {
+            "time": 0,
+            "rgba": [
+              127,
+              0,
+              126,
+              255
+            ],
+            "readyState": 4,
+            "decoded": 4,
+            "total": 4,
+            "box": {
+              "width": 320,
+              "height": 180
+            }
+          },
+          "codeSha256": "808efa8818d5f317a92777ada48d39dfaadb9c6eba63845ff42b606dadfc60c8"
+        },
+        {
+          "engine": "firefox",
+          "browser": "155.0",
+          "variant": "current",
+          "outcome": "completed",
+          "firstFrameMatches": true,
+          "firstDraw": {
+            "time": 0,
+            "rgba": [
+              137,
+              19,
+              126,
+              255
+            ],
+            "readyState": 4,
+            "total": 0,
+            "box": {
+              "width": 320,
+              "height": 180
+            }
+          },
+          "codeSha256": "6080dd90bde239515646899bdd8e71d17de24119523e4883025fbf39b1a6a302"
+        },
+        {
+          "engine": "firefox",
+          "browser": "155.0",
+          "variant": "layout-before-src",
+          "outcome": "completed",
+          "firstFrameMatches": true,
+          "firstDraw": {
+            "time": 0,
+            "rgba": [
+              137,
+              19,
+              126,
+              255
+            ],
+            "readyState": 4,
+            "total": 0,
+            "box": {
+              "width": 320,
+              "height": 180
+            }
+          },
+          "codeSha256": "808efa8818d5f317a92777ada48d39dfaadb9c6eba63845ff42b606dadfc60c8"
+        }
+      ]
+    }
+  ],
+  "validation": {
+    "lint": {
+      "file": "refactor/.cache/auto-native-lint.log",
+      "sha256": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "exitCode": 0
+    },
+    "nativeCases": 18,
+    "webkitFirstFrameFailures": 6,
+    "successfulEngineControls": 12,
+    "planAndRisk": {
+      "file": "refactor/.cache/auto-native-final.log",
+      "sha256": "db44816eb60ba734d6c5991b7031e9a4f4d30bce467f5fbf699c0cf30f52fe85",
+      "exitCode": 0
+    }
+  },
+  "limitations": [
+    "Windows host only; not exact Safari/device diagnosis",
+    "Original acceptance pixels/media unchanged; no-B-frame media is only a diagnostic control",
+    "No production source or declaration change",
+    "No task completion or risk closure",
+    "Current upstream source is contextual, not an exact installed binary match",
+    "Cached exploratory variants are not production lifecycle implementations"
+  ]
+}
diff --git a/refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-native-decoder.md b/refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-native-decoder.md
new file mode 100644
index 000000000..54fbfbe6c
--- /dev/null
+++ b/refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-native-decoder.md
@@ -0,0 +1,72 @@
+# PKG-AUTO-THUMB-03: isolate the native decoder boundary
+
+Checkpoint from 772d79a67196ff61dc1e90499c275fee936cb942. Task03 and
+AUTO-THUMB-PIXEL-01 remain open; no source fix, completion or publication is claimed.
+
+## New evidence
+
+The earlier first-seek experiments still imported the plugin. This checkpoint
+adds `refactor/scripts/auto-thumbnail-native-probe.mjs` and the root command
+`yarn probe:auto-thumbnail-native` to remove that dependency. It imports neither
+ArtPlayer nor the thumbnail factory: only a native video, canvas, Playwright and
+the already-verified local dev HTTP server. The original frozen MP4 remains
+byte-identical. A separately generated H.264 variant with B frames disabled probes
+whether frame reordering alone explains the observation; it is never substituted
+for the original acceptance sample. FFmpeg decoding must show a purple first
+pixel in both files before the browser run begins.
+
+The final18 cases cover2 media files,3 browsers and3 native modes: hidden paused,
+visible paused and hidden play-then-immediate-pause. Every case records31 draws,
+native events, currentTime, readyState, paused/seeking flags and RGBA. Requested
+16ms sample timers run slower in Windows WebKit; elapsed times are retained rather
+than pretending the nominal half-second is exact. All6 WebKit26.6 cases miss the
+purple first frame. Visible original video eventually yields red while time stays0;
+other WebKit cases remain transparent. All12 Chromium153.0.8010.12/Firefox155.0
+controls obtain purple. This proves the issue can occur without our plugin on
+this Windows host; it does not prove the cause in all WebKit/Safari backends.
+
+The initial12-case run omitted visible-paused; its report is retained separately.
+The final capture adds visible control and bounds native play Promise waiting.
+Results, media metadata, FFmpeg version/arguments, source and raw-report hashes
+are in [auto-thumbnail-native-decoder.json](../baselines/auto-thumbnail-native-decoder.json).
+
+Exploratory current-bundle variants also failed: zero/slow playback rate,
+fastSeek(0), zero-rate play; first-seek offsets1us/1ms/16ms; layout before src,
+two paints before src, layout after metadata and two paints after metadata.
+The zero-rate play variant timed out, so it supplies no completed drawing result.
+These cache-only experiments are not production cancellation implementations or
+accepted fixes. Raw output and script/report hashes are retained for diagnosis.
+One exploratory launch failed before browser execution because a data URL could
+not resolve the bare Playwright import; executing a real cache .mjs fixed the
+runner. No pixel assertion was relaxed to hide these outcomes.
+
+## Source interpretation and next action
+
+Current upstream [Windows Media Foundation implementation](https://github.com/WebKit/WebKit/blob/main/Source/WebCore/platform/graphics/win/MediaPlayerPrivateMediaFoundation.cpp)
+starts a native session for seeking and resolves seek completion from the session
+started handler, separately from frame painting. That source makes a timing/surface
+boundary plausible; it is not the pinned binary's exact source revision and is
+not proof of the underlying defect. Runtime captures above are the actual evidence.
+
+Do not add an arbitrary wait, first-time offset or sample replacement to pass this
+host's gate. The next useful pixel investigation requires another supported native
+backend/device or an explicit decoded-frame path. No change to task03 acceptance,
+the first-frame pixel check, public time formula or declared browser support is
+authorized by this checkpoint. Other resource/typing/combination work may proceed
+without calling this defect fixed.
+
+## Reproduction, ownership and validation
+
+Run under canonical Node24.21.0/Yarn1.22.22 with installed FFmpeg and FFprobe.
+Optional FFMPEG/FFPROBE specify executable paths. No new npm dependency, lock or
+package artifact change; the probe is explicit, not added to regular CI because
+it needs the external encoder binaries. It owns its random-port server, browser
+instances/pages and video/canvas cleanup, and retains only its generated diagnostic
+directory. Existing8082 remains untouched. It creates no real workspace package.
+
+The command's successful exit means capture completed, not pixel acceptance.
+Targeted script lint and plan/risk checks validate only this changed diagnostic and
+metadata. Production tests are not rerun because runtime/type/acceptance-test files
+are unchanged. The package maintenance guide explains the new diagnostic boundary.
+Commit as a task03 checkpoint; revert that commit to remove this diagnostic and
+records together. Local only, no push or publication.
diff --git a/refactor/plan.md b/refactor/plan.md
index 4d616588a..1d344131a 100644
--- a/refactor/plan.md
+++ b/refactor/plan.md
@@ -530,7 +530,7 @@
 - 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) [记录](changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md) [记录](baselines/auto-thumbnail-rendering-readiness.json) [记录](changes/2026-09-14-PKG-AUTO-THUMB-03-first-seek.md) [记录](baselines/auto-thumbnail-first-seek.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) [记录](changes/2026-09-14-PKG-AUTO-THUMB-03-first-seek.md) [记录](baselines/auto-thumbnail-first-seek.json) [记录](changes/2026-09-14-PKG-AUTO-THUMB-03-native-decoder.md) [记录](baselines/auto-thumbnail-native-decoder.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 a65212b51..aa0e3a0cc 100644
--- a/refactor/progress.md
+++ b/refactor/progress.md
@@ -1,5 +1,19 @@
 # 进度与证据
 
+## Auto Thumbnail 原生首帧边界检查点
+
+新增独立 video/canvas 诊断，完全不加载 ArtPlayer 或插件。冻结原视频不变，另用
+FFmpeg生成无B帧对照，确认两文件首帧均为紫色。Windows三引擎/两文件/三模式
+共18组：WebKit26.6六组均未得到紫色，Chromium/Firefox十二组得到；可见视频也
+会在currentTime0读到后续红帧。此证据将问题缩小到该宿主的原生画面路径，不能
+推断所有Safari或标为修复。速率、微小seek偏移和布局/绘制等待的探索同样无效，
+没有采用绕过首帧断言的方案。命令、实际FFmpeg/浏览器版本、事件/像素和报告指纹
+见[检查点](changes/2026-09-14-PKG-AUTO-THUMB-03-native-decoder.md)和[证据](baselines/auto-thumbnail-native-decoder.json)。
+源码/类型/分发与像素验收未改，仅新增诊断脚本和文档；目标lint与计划/风险检查
+通过。PKG-AUTO-THUMB-03/AUTO-THUMB-PIXEL-01保持开放，245项/173 done不变。
+下一步按原生边界选择其他支持后端/设备取证，同时继续该包的资源与异步边界审查；
+不重复追加任意等待。VAST默认行为选择仍待答复。本地检查点提交，无推送/发布。
+
 ## MOD-DEV-01 自有开发服务器与关闭流程完成
 
 HTTP、静态资源与 SSE 拆为严格 TS 模块，修复 Servor4.0.2 端口占用却退出0的
diff --git a/refactor/risks.json b/refactor/risks.json
index 06ceefaf0..e740fea03 100644
--- a/refactor/risks.json
+++ b/refactor/risks.json
@@ -4187,11 +4187,13 @@
         "refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md",
         "refactor/baselines/auto-thumbnail-rendering-readiness.json",
         "refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-first-seek.md",
-        "refactor/baselines/auto-thumbnail-first-seek.json"
+        "refactor/baselines/auto-thumbnail-first-seek.json",
+        "refactor/changes/2026-09-14-PKG-AUTO-THUMB-03-native-decoder.md",
+        "refactor/baselines/auto-thumbnail-native-decoder.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. 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. First-seek diagnostics additionally exclude drawing the first loadeddata frame without seek, one/two RAF waits, post-seek RAF waits and verified forward/back seeking on the recorded Windows WebKit host. The warm comparison first had an invalid stale-event completion, then a timeout; final bounded retries verify actual [1,1,0] seeking and still miss purple. Controls retain purple. These are exclusions, not production fixes.",
       "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."
+      "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. Native-only18-case Windows probe also misses the purple first frame in all6 WebKit26.6 cases (hidden/visible paused and immediate play-pause, original and no-B-frame H.264);12 Chromium/Firefox controls recover it. No ArtPlayer/plugin is imported, narrowing but not resolving the native surface boundary. Rate/offset/layout explorations failed and must not be reintroduced as assumed fixes."
     },
     {
       "id": "VTT-THUMB-DIST-01",
diff --git a/refactor/scripts/auto-thumbnail-native-probe.mjs b/refactor/scripts/auto-thumbnail-native-probe.mjs
new file mode 100644
index 000000000..2cab49739
--- /dev/null
+++ b/refactor/scripts/auto-thumbnail-native-probe.mjs
@@ -0,0 +1,118 @@
+import assert from 'node:assert/strict'
+import { execFileSync } from 'node:child_process'
+import { createHash } from 'node:crypto'
+import fs from 'node:fs'
+import path from 'node:path'
+import process from 'node:process'
+import { chromium, firefox, webkit } from '@playwright/test'
+import { startDevServer } from '../../scripts/library/server.ts'
+
+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-native')
+assert.equal(process.argv.length, 2, 'No probe arguments are supported')
+const fingerprint = data => createHash('sha256').update(data).digest('hex')
+const original = 'test/browser/media/auto-thumbnail-timeline.mp4'
+const originalBytes = fs.readFileSync(original)
+assert.equal(fingerprint(originalBytes), JSON.parse(fs.readFileSync('refactor/baselines/auto-thumbnail-timeline-media.json')).file.sha256)
+const directory = fs.mkdtempSync('refactor/.cache/auto-thumbnail-native-')
+fs.writeFileSync(path.join(directory, 'index.html'), '<!doctype html><title>Native decoder diagnostic</title>')
+fs.copyFileSync(original, path.join(directory, 'original.mp4'))
+const ffmpeg = process.env.FFMPEG || 'ffmpeg'
+const ffprobe = process.env.FFPROBE || 'ffprobe'
+const args = ['-hide_banner', '-loglevel', 'error', '-n', '-i', original, '-map', '0:v:0', '-an', '-c:v', 'libx264', '-pix_fmt', 'yuv420p', '-bf', '0', '-g', '30', '-crf', '18', '-movflags', '+faststart', path.join(directory, 'no-b-frames.mp4')]
+execFileSync(ffmpeg, args, { windowsHide: true })
+const ffmpegVersion = execFileSync(ffmpeg, ['-version'], { encoding: 'utf8', windowsHide: true }).split('\n')[0].trim()
+const media = ['original.mp4', 'no-b-frames.mp4'].map((name) => {
+  const file = path.join(directory, name)
+  const metadata = JSON.parse(execFileSync(ffprobe, ['-v', 'error', '-select_streams', 'v:0', '-show_entries', 'stream=codec_name,profile,time_base,start_time,duration,has_b_frames', '-of', 'json', file], { encoding: 'utf8', windowsHide: true }))
+  const raw = execFileSync(ffmpeg, ['-v', 'error', '-i', file, '-frames:v', '1', '-vf', 'scale=1:1', '-pix_fmt', 'rgba', '-f', 'rawvideo', 'pipe:1'], { windowsHide: true })
+  assert.equal(raw.length, 4)
+  assert(raw[0] > 100 && raw[2] > 100 && raw[1] < 40, 'Both files must actually decode a purple first frame')
+  return { file, sha256: fingerprint(fs.readFileSync(file)), metadata, ffmpegFirstPixel: [...raw] }
+})
+const errors = []
+const server = await startDevServer({ root: directory, port: 0, onError: error => errors.push(String(error)) })
+const results = []
+console.log(`Native decoder diagnostics: ${directory}`)
+try {
+  for (const [engineName, engine] of Object.entries({ webkit, chromium, firefox })) {
+    const browser = await engine.launch()
+    try {
+      for (const file of ['original.mp4', 'no-b-frames.mp4']) {
+        for (const mode of ['paused', 'visible-paused', 'play-pause']) {
+          const page = await browser.newPage()
+          try {
+            await page.goto(server.url)
+            const result = await page.evaluate(async ({ file, mode }) => {
+              const video = document.createElement('video')
+              video.width = 320
+              video.height = 180
+              video.muted = true
+              video.playsInline = true
+              video.style.cssText = 'position:fixed;visibility:hidden;width:320px;height:180px'
+              if (mode === 'visible-paused')
+                video.style.visibility = 'visible'
+              document.body.append(video)
+              const canvas = document.createElement('canvas')
+              canvas.width = 320
+              canvas.height = 180
+              const context = canvas.getContext('2d')
+              const samples = []
+              const events = []
+              const started = performance.now()
+              let timer
+              const state = () => ({ elapsed: performance.now() - started, time: video.currentTime, readyState: video.readyState, paused: video.paused, seeking: video.seeking })
+              for (const name of ['loadedmetadata', 'loadeddata', 'canplay', 'play', 'playing', 'pause', 'seeked', 'error'])
+                video.addEventListener(name, () => events.push({ name, ...state() }))
+              try {
+                const ready = new Promise((resolve, reject) => {
+                  video.onloadeddata = resolve
+                  video.onerror = () => reject(new Error(`Media error ${video.error?.code}`))
+                  timer = setTimeout(() => reject(new Error('Native loadeddata timeout')), 8000)
+                })
+                video.src = `/${file}`
+                await ready
+                clearTimeout(timer)
+                if (mode === 'play-pause') {
+                  await Promise.race([
+                    video.play(),
+                    new Promise((_, reject) => { timer = setTimeout(() => reject(new Error('Native play timeout')), 8000) }),
+                  ])
+                  clearTimeout(timer)
+                  video.pause()
+                }
+                for (let index = 0; index < 31; index++) {
+                  context.clearRect(0, 0, 320, 180)
+                  context.drawImage(video, 0, 0)
+                  samples.push({ ...state(), rgba: [...context.getImageData(160, 90, 1, 1).data] })
+                  await new Promise(resolve => setTimeout(resolve, 16))
+                }
+                return { samples, events, mediaError: video.error?.code || 0, supportsFrames: typeof video.requestVideoFrameCallback === 'function' }
+              }
+              finally {
+                clearTimeout(timer)
+                video.pause()
+                video.removeAttribute('src')
+                video.load()
+                video.remove()
+                canvas.width = canvas.height = 0
+              }
+            }, { file, mode })
+            const purple = result.samples.filter(({ rgba: [r, g, b, a] }) => a === 255 && Math.min(r, b) > 100 && Math.abs(r - b) < 30 && g < 40)
+            const entry = { engine: engineName, browser: browser.version(), file, mode, purpleSamples: purple.length, ...result }
+            results.push(entry)
+            console.log(JSON.stringify({ engine: engineName, file, mode, purpleSamples: purple.length, first: result.samples[0], last: result.samples.at(-1) }))
+          }
+          finally { await page.close() }
+        }
+      }
+    }
+    finally { await browser.close() }
+  }
+}
+finally {
+  await server.close()
+  assert.deepEqual(errors, [])
+  assert.equal(fingerprint(fs.readFileSync(original)), fingerprint(originalBytes))
+  fs.writeFileSync(path.join(directory, 'report.json'), `${JSON.stringify({ task: 'PKG-AUTO-THUMB-03', capturedAt: new Date().toISOString(), node: process.version, platform: process.platform, ffmpegVersion, args, media, results, scope: 'Native video/canvas only; no ArtPlayer/plugin imported. No-seek hidden/visible paused and hidden play-pause controls capture31 draws separated by16ms requested timers; actual elapsed durations are recorded. The no-B-frame transcode is diagnostic only and never replaces the frozen acceptance fixture. Counts report observations, not acceptance or a production fix.' }, null, 2)}\n`)
+}
diff --git a/refactor/tasks.json b/refactor/tasks.json
index 49fde8d10..3428698c7 100644
--- a/refactor/tasks.json
+++ b/refactor/tasks.json
@@ -1801,7 +1801,9 @@
         "changes/2026-09-14-PKG-AUTO-THUMB-03-rendering-readiness.md",
         "baselines/auto-thumbnail-rendering-readiness.json",
         "changes/2026-09-14-PKG-AUTO-THUMB-03-first-seek.md",
-        "baselines/auto-thumbnail-first-seek.json"
+        "baselines/auto-thumbnail-first-seek.json",
+        "changes/2026-09-14-PKG-AUTO-THUMB-03-native-decoder.md",
+        "baselines/auto-thumbnail-native-decoder.json"
       ]
     },
     {