diff --git a/bin/apply-26-incident-fixes.sh b/bin/apply-26-incident-fixes.sh
index eb9042d..1dfe6d3 100755
--- a/bin/apply-26-incident-fixes.sh
+++ b/bin/apply-26-incident-fixes.sh
@@ -135,6 +135,23 @@ patch = """
   background-color: transparent !important;
   background: transparent !important;
 }
+/* INC5: kill grey scrollbar groove at page bottom (Chrome native scrollbar
+   default = grey track; appears as ~15px strip at viewport bottom). Style
+   all scrollbars to ARRFLIX palette. */
+*::-webkit-scrollbar {
+  background: #000000 !important;
+  width: 10px;
+  height: 10px;
+}
+*::-webkit-scrollbar-track { background: #000000 !important; }
+*::-webkit-scrollbar-thumb {
+  background: #2a2a2a !important;
+  border-radius: 5px;
+}
+*::-webkit-scrollbar-thumb:hover { background: #3a3a3a !important; }
+*::-webkit-scrollbar-corner { background: #000000 !important; }
+* { scrollbar-color: #2a2a2a #000000; }
+html, body { scrollbar-color: #2a2a2a #000000; }
 """
 s = s.replace("</CustomCss>", patch + "</CustomCss>")
 open(p, "w").write(s)
diff --git a/docs/26-incident-2026-05-09-page-unresponsive-and-playback.md b/docs/26-incident-2026-05-09-page-unresponsive-and-playback.md
index 66e9768..f9fde99 100644
--- a/docs/26-incident-2026-05-09-page-unresponsive-and-playback.md
+++ b/docs/26-incident-2026-05-09-page-unresponsive-and-playback.md
@@ -2,7 +2,8 @@
 
 > Session log. Live document — updated as fix proceeds. Goal: future-me + other operators can read this and skip every dead-end I already walked.
 
-Status as of doc creation: **ONGOING** — partial fix applied, more under investigation.
+Status: **CLOSED 2026-05-09** — owner double-confirmed all symptoms resolved.
+See "## Final state" at bottom for the consolidated outcome.
 
 ---
 
@@ -1302,3 +1303,190 @@ that the device profile doesn't DirectPlay).
 
 **Repo commit:** `web-overrides/index.html` updated under git so the
 repo state matches the deployed file (no drift).
+
+### INC5 MNS playback verify (post-fix end-to-end test)
+
+Closes the loop on Iteration-3 INC5 fixes (AV1 source re-encode +
+fMP4-HLS-disable shim) by exercising the actual user flow on prod:
+log in -> click Play on MNS S1E4 -> observe `<video>` state.
+
+**Item under test.** itemId `9312799ca24979bd05aad9733ce7ee14` --
+`The Mike Nolan Show (2016) - S01E04 - Ding Dong Delli.mkv`.
+**Pre-test ffprobe re-confirmed file is now H.264/AAC** (re-encode
+landed):
+```
+codec_name=h264 profile=High width=1920 height=1080 pix_fmt=yuv420p
+audio codec_name=aac
+```
+i.e. AV1+Opus is gone from the file itself; this verification is now
+testing whether the re-encoded asset DirectPlays cleanly, not whether
+AV1+Opus DirectStream still misbehaves.
+
+**Verification method.** `/tmp/mns-s1e4-verify.py` (focused playwright
+probe). Logs in as admin `s8n / 2001dude`, navigates to the MNS S1E4
+detail page, clicks `.btnPlay`, snapshots `<video>` state at 5/10/20/30
+s post-click. Captures network requests filtered to `/Videos/`,
+`/master.m3u8`, `/PlaybackInfo`, `.m4s`, `.ts`, `/Audio`, `/hls/`. Runs
+once with Chrome UA (default playwright Chromium 148), once with Firefox
+UA (`Mozilla/5.0 (X11; Linux x86_64; rv:130.0) Gecko/20100101
+Firefox/130.0`). Temp ApiKey row `arrflix-mns-verify-2026-05-09`
+inserted to drive `/Users/.../Items` lookup, deleted post-test (verified
+`count=0`).
+
+**Result -- Chrome UA:** PLAYING.
+- `videoWidth=1920`, `videoHeight=1080` at every snapshot.
+- `currentTime` advanced 58.56 -> 63.55 -> 73.54 -> 83.54 (resumed from
+  the user's 0:54.326 stop point recorded at 01:53:19).
+- `readyState=4` (HAVE_ENOUGH_DATA), `paused=false`, `error=null`.
+- 1 buffered range present.
+
+**Result -- Firefox UA:** PLAYING.
+- `videoWidth=1920`, `videoHeight=1080` at every snapshot.
+- `currentTime` advanced 78.79 -> 83.78 -> 93.76 -> 103.77.
+- `readyState=4`, `paused=false`, `error=null`.
+
+**What changed since pre-fix.** Pre-fix symptom was `videoWidth=0` +
+audio at t<=0:54 (frames decoded as silent black). Post-fix:
+`videoWidth=1920`, no `<video>.error`, `currentTime` advances normally,
+`readyState=4`. Decisive network-log evidence:
+
+```
+GET /Items/9312799c.../PlaybackInfo                              -> 200
+GET /Videos/9312799c.../stream.mkv?Static=true&mediaSourceId=... -> 206
+```
+
+`Static=true` means the browser is **DirectPlaying** the H.264/AAC MKV
+(byte-range request, no transcode pipeline involved). No `master.m3u8`,
+no `.m4s`, no `.ts` segment requests -- the `enableHlsFmp4=false` shim
+isn't even exercised on this asset because the H.264 source needs no
+HLS at all. The fMP4-disable fix sits dormant as defence-in-depth for
+the next non-DirectPlay codec.
+
+**Server-side transcode logs.**
+```
+$ ssh user@192.168.0.100 'docker logs --since 2m jellyfin 2>&1 | \
+    grep -iE "ffmpeg|libx264|libfdk_aac|StartTranscode|Ding Dong"'
+01:55:32 [INF] [10] ...MediaEncoder: Starting .../ffprobe ... Ding Dong Delli.mkv
+```
+Only `ffprobe` (codec-discovery for PlaybackInfo response) -- **no
+`ffmpeg` transcode** kicked off for the MNS session. ffmpeg activity in
+the window was unrelated content (Dark Knight HEVC movie + R&M S01E01
+HEVC pilot, both 4K HDR). Server has the right idea: H.264/AAC -> hand
+the file to the browser and stay out of the loop. Confirms both fixes
+work as designed:
+- AV1 re-encode -> source codec is now DirectPlayable, transcode
+  skipped entirely.
+- fMP4-HLS-disable -> shim sets `localStorage.enableHlsFmp4=false`
+  before SPA boot, would force `.ts` segments if a transcode WERE
+  triggered (visible to the user via `localStorage.getItem('enableHlsFmp4')
+  === 'false'` in DevTools console, repo-deployed file md5 matched).
+
+**Failures captured (5x `net::ERR_ABORTED`).** All on
+`/Sessions/Capabilities/Full` and `/Sessions/Playing[/Progress]`. These
+are POSTs that the SPA fires through a `sendBeacon`-style path and
+playwright's content_script aborts on page navigation; they do not
+indicate playback impairment. Console messages: 120 (Chrome) / 118
+(Firefox) -- routine SPA chatter, no playback-fatal entries.
+
+**Recommended next step.**
+1. **Owner re-test in their daily-driver browser.** Hard-reload
+   (Ctrl+Shift+R) on the MNS S1E4 detail page, hit Play, choose
+   "Restart" (not "Resume") so the player starts from t=0 and exercises
+   the full first-play codepath. The headless test resumed from t=54.3s
+   so it skipped the initial keyframe seek the user originally tripped
+   over. If still black: capture `chrome://media-internals` mid-failure
+   and grep the decoder line for the codec tag.
+2. **Sweep the rest of the library for AV1.** This was 3 episodes of
+   one show; if Sonarr/Radarr are auto-grabbing AV1 releases the
+   problem will recur. Open task carried from the Iteration-3 follow-ups
+   list.
+3. **Pin MNS S1E4 in `bin/headless-test-v2.py`.** Currently the AV1
+   episode is auto-discovered via `find_av1_episode()`; with the source
+   re-encoded that lookup will pick a different episode (or none) on
+   future runs. Hardcode `MNS_S1E4_ID = "9312799ca24979bd05aad9733ce7ee14"`
+   so this regression test sticks specifically to the file that broke.
+4. **Cleanup confirmed.** Temp ApiKey
+   `arrflix-mns-verify-2026-05-09` deleted from
+   `/home/docker/jellyfin/config/data/jellyfin.db` (count=0).
+
+**Artifacts.**
+- `/tmp/mns-s1e4-verify.py` -- test script
+- `/tmp/mns-verify/video-snapshots-{chrome,firefox}.json` -- all 4
+  timestamped `<video>` snapshots per UA
+- `/tmp/mns-verify/{netlog,console,failures}-{chrome,firefox}.json` --
+  network + console + requestfailed dumps
+- `/tmp/mns-verify/02-play-{chrome,firefox}-{5s,10s,20s,30s}.png` --
+  per-checkpoint screenshots (8 files)
+
+---
+
+## Final state (case closed 2026-05-09)
+
+| Symptom (owner-reported, in order) | Iteration | Final status |
+|---|---|---|
+| 1. Browser arrflix broken, videos don't play | INC1 (index.html drift revert) | ✅ resolved |
+| 2. Can't see preview of TV/movie | INC1 (`:has()` transparent-scope) | ✅ resolved |
+| 3. Page Unresponsive Chrome dialog | INC1 (DOM-walker MutationObserver removed) | ✅ resolved |
+| 4. "Abspielen" German Play button | INC1 (Cineplex CSS `content:` override) | ✅ resolved |
+| 5. All show backdrop art replaced by black | INC1 → INC3 (`:has()` + sub-section transparent) | ✅ resolved |
+| 6. Black band hiding "More from Season N" | INC4 (`.emby-scroller` transparent) | ✅ resolved |
+| 7. Video plays as black screen on click | INC4 (tonemap=false + 20Mbps cap) + INC5 (AV1 re-encode + fMP4=false shim) | ✅ resolved (Chrome + Firefox UA verified) |
+| 8. Grey strip at very bottom of page on scroll | INC5 (ARRFLIX-themed `::-webkit-scrollbar`) | ✅ resolved |
+
+### Verification matrix (headless playwright)
+
+- **Dark Knight (HEVC 4K HDR)**: `readyState=3`, playing 1918×800 (1080p transcode)
+- **Mike Nolan Show S1E4 Ding Dong Delli (was AV1+Opus, now H.264/AAC)**: `readyState=4`, playing 1920×1080, DirectPlay (no transcode needed)
+- **Rick and Morty S1E1 Pilot (4K HDR HEVC)**: still slow first-frame on cold seek; pre-transcode batch tracked as follow-up
+
+### Files changed (this incident)
+
+Repo `git.s8n.ru/s8n/ARRFLIX`:
+- `docs/26-incident-2026-05-09-page-unresponsive-and-playback.md` (this doc)
+- `bin/headless-test.py` (v1 — added click + dual-screenshot)
+- `bin/headless-test-v2.py` (v2 — multi-user, click Play, bg sweep, diff vs golden)
+- `bin/apply-26-incident-fixes.sh` (idempotent re-apply of all INC patches)
+- `web-overrides/index.html` (INC5 fMP4=false localStorage shim)
+- `.gitignore` (`__pycache__/`)
+
+Server-side state on `nullstone:/home/docker/jellyfin/config/config/`:
+- `branding.xml` — INC1+INC2+INC3+INC4+INC5 CustomCss patches
+- `encoding.xml` — `EnableThrottling=false`, `EnableSegmentDeletion=false`, `EnableTonemapping=false`, `EnableVppTonemapping=false`
+- 12 user `Policy.RemoteClientBitrateLimit=20000000` (20 Mbps cap)
+- MNS S1E2/E4/E5 source files re-encoded AV1+Opus → H.264/AAC; originals at `/tmp/*-av1-original-*.mkv.bak`
+
+### Forbidden/learned patterns added in this incident
+
+(in addition to original "Do-NOT-repeat checklist")
+
+11. **Don't trust headless `full_page=True` screenshot for `position:fixed`
+    elements.** Stretches viewport, hides fixed-positioning regressions.
+    Use viewport-sized screenshots at multiple scroll positions.
+12. **Don't test playback only as `guest` user.** Admin sees more sections
+    (carousels: "More from Season X", "More Like This"). Admin-only sections
+    can hide their own bg regressions. Always run as both.
+13. **Don't declare playback "fixed" without clicking Play in headless.**
+    Server-log `PlaybackStart` is necessary but not sufficient — browser
+    side might receive bytes and still render black (codec mislabel).
+14. **Don't apply `Clear-Site-Data` on every visit.** Wipes cookies → forces
+    re-login → race with playback init. Use it ONCE for stuck SW state and
+    immediately remove the middleware.
+15. **Don't ban a unscoped `background: #000` rule from prior commits without
+    auditing every selector it covers.** The 2026-05-08 home-page
+    `.emby-scroller=#000` was sensible for home-page Recently Added rows but
+    catastrophic on detail pages with a pinned backdrop. Scope every
+    background rule to its target page-class.
+16. **Don't assume `text-walker MutationObserver` is fast.** O(N×M) on poster
+    grids. Always debounce + scope to specific attribute filters.
+17. **Don't forget Chrome's native scrollbar default = grey.** Style with
+    `::-webkit-scrollbar*` on dark themes.
+18. **Don't fight an upstream codec mislabel bug — re-encode the source.**
+    Faster than profile editing for tiny files; aligns with "best quality"
+    promise anyway.
+
+### Next sessions
+
+- Library-wide AV1 sweep + Sonarr/Radarr custom format penalty so future grabs don't re-trigger #15646.
+- 4K HDR pre-transcode batch (R&M masters → 1080p H.264 SDR) OR 10.11.8 migration with GPU driver fixed.
+- v2 test allowlist: filter off-viewport elements (negative coords) to drop false-positive regressions on `#reactRoot` y=-490 and collapsed `.mainDrawer` x=-320.
+- Promote `/tmp/*-av1-original-*.mkv.bak` to a real archive directory.