diff --git a/bin/apply-26-incident-fixes.sh b/bin/apply-26-incident-fixes.sh
index 1dfe6d3..2b53c9e 100755
--- a/bin/apply-26-incident-fixes.sh
+++ b/bin/apply-26-incident-fixes.sh
@@ -135,6 +135,19 @@ patch = """
   background-color: transparent !important;
   background: transparent !important;
 }
+/* INC7 2026-05-09: BLACK-PASS paints .libraryPage #000; #videoOsdPage uses
+   that class so the OSD page covers <video> with opaque black. <video>
+   decodes frames (canvas drawImage luma=84) but visually 100% black until
+   we exempt the OSD page from BLACK-PASS via :has(.htmlVideoPlayer). */
+.libraryPage:has(.htmlVideoPlayer),
+.libraryPage#videoOsdPage,
+#videoOsdPage,
+#videoOsdPage .pageContainer,
+#videoOsdPage .layout-desktop,
+#videoOsdPage .mainAnimatedPages {
+  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. */
diff --git a/bin/prod-vs-dev-compare.py b/bin/prod-vs-dev-compare.py
index 1a3b6f3..bbd8048 100755
--- a/bin/prod-vs-dev-compare.py
+++ b/bin/prod-vs-dev-compare.py
@@ -311,6 +311,37 @@ async def run_side(p, side_cfg):
                 paintRGBSum = (r+g+b)/n;
                 paintOk = paintLuma > 4;  // > a few luma above pure black
             } catch (e) { paintErr = String(e); }
+            // Stacking diagnosis: who's on top of the video center?
+            const r = v.getBoundingClientRect();
+            const cx = r.x + r.width/2, cy = r.y + r.height/2;
+            let stackAtVideoCenter = [];
+            try {
+                const els = (typeof document.elementsFromPoint === 'function')
+                    ? document.elementsFromPoint(cx, cy) : [];
+                stackAtVideoCenter = els.slice(0, 6).map(e => {
+                    const cs = getComputedStyle(e);
+                    return {
+                        tag: e.tagName.toLowerCase(),
+                        id: e.id || null,
+                        cls: (typeof e.className === 'string' ? e.className : '').slice(0, 80),
+                        bg: cs.backgroundColor,
+                        opacity: cs.opacity,
+                        zIndex: cs.zIndex,
+                        position: cs.position,
+                        isVideo: e === v,
+                    };
+                });
+            } catch (e) {}
+            const osd = document.getElementById('videoOsdPage');
+            const osdInfo = osd ? {
+                bg: getComputedStyle(osd).backgroundColor,
+                display: getComputedStyle(osd).display,
+                opacity: getComputedStyle(osd).opacity,
+                position: getComputedStyle(osd).position,
+                zIndex: getComputedStyle(osd).zIndex,
+                cls: osd.className,
+                rect: osd.getBoundingClientRect().toJSON ? osd.getBoundingClientRect().toJSON() : null,
+            } : null;
             return {
                 present: true,
                 src: v.src || '',
@@ -327,6 +358,8 @@ async def run_side(p, side_cfg):
                 bufferedRanges: v.buffered.length,
                 bufferedEnd: v.buffered.length ? v.buffered.end(v.buffered.length-1) : 0,
                 paintLuma, paintRGBSum, paintOk, paintErr,
+                stackAtVideoCenter,
+                videoOsdPage: osdInfo,
             };
         }""")
         samples.append({"t": t, "video": snap})
@@ -512,6 +545,20 @@ def render_md(diff, prod, dev):
         if dp_ok is False and pp_ok is True:
             return ("dev fails because <video> advances time but paints all-black "
                     "(paintLuma~0) while prod paints normally")
+        # OSD overlay check
+        def topel(s): return (s.get("stackAtVideoCenter") or [{}])[0]
+        pt = topel(last_p); dt = topel(last_d)
+        def is_opaque_black(bg):
+            if not bg: return False
+            try:
+                nums = [int(x) for x in bg.replace("rgba(","").replace("rgb(","").replace(")","").split(",")[:3]]
+                return sum(nums) < 30
+            except Exception: return False
+        if (not pt.get("isVideo")) and is_opaque_black(pt.get("bg")) \
+           and (dt.get("isVideo") or not is_opaque_black(dt.get("bg"))):
+            return (f"prod fails because an opaque-black `{pt.get('tag')}#{pt.get('id') or ''}"
+                    f".{pt.get('cls')}` element is rendered on top of the <video> "
+                    f"(bg={pt.get('bg')}); dev's video is uncovered")
         return "neither side errored or painted black explicitly — see HTTP/PlaybackInfo/cmdline diffs"
 
     md = []
@@ -529,6 +576,27 @@ def render_md(diff, prod, dev):
               "videoWidth", "videoHeight", "bufferedRanges", "bufferedEnd",
               "paintLuma", "paintRGBSum", "paintOk"]:
         md.append(f"| {k} | `{last_p.get(k)}` | `{last_d.get(k)}` |")
+    # OSD page styling diff (the smoking gun for prod black-screen)
+    p_osd = last_p.get("videoOsdPage") or {}
+    d_osd = last_d.get("videoOsdPage") or {}
+    md.append("")
+    md.append("## #videoOsdPage style (the OSD container painted on top of the <video>)")
+    md.append("| Field | prod | dev |")
+    md.append("|---|---|---|")
+    for k in ["bg", "opacity", "position", "zIndex", "display", "cls"]:
+        md.append(f"| {k} | `{p_osd.get(k)}` | `{d_osd.get(k)}` |")
+    md.append("")
+    md.append("## Stack at video center (top → bottom)")
+    md.append("### prod")
+    for s in (last_p.get("stackAtVideoCenter") or []):
+        md.append(f"- `{s.get('tag')}#{s.get('id')}.{s.get('cls')}` "
+                  f"bg=`{s.get('bg')}` z=`{s.get('zIndex')}` pos=`{s.get('position')}` "
+                  f"isVideo={s.get('isVideo')}")
+    md.append("### dev")
+    for s in (last_d.get("stackAtVideoCenter") or []):
+        md.append(f"- `{s.get('tag')}#{s.get('id')}.{s.get('cls')}` "
+                  f"bg=`{s.get('bg')}` z=`{s.get('zIndex')}` pos=`{s.get('position')}` "
+                  f"isVideo={s.get('isVideo')}")
     md.append("")
     md.append("## Stream URL (decoded)")
     md.append(f"- **prod**: `{diff.get('stream_url_prod') or '(empty)'}`")
diff --git a/docs/28-prod-vs-dev-playback-divergence-2026-05-09.md b/docs/28-prod-vs-dev-playback-divergence-2026-05-09.md
index 1b51ae3..0217969 100644
--- a/docs/28-prod-vs-dev-playback-divergence-2026-05-09.md
+++ b/docs/28-prod-vs-dev-playback-divergence-2026-05-09.md
@@ -332,3 +332,267 @@ Repo commit (this doc + bin/prod-vs-dev-compare.py): `917d21b3be5f8de198ff9b9659
 - Pushed to `origin main` on `git.s8n.ru/s8n/ARRFLIX` at 2026-05-09 02:46Z
 
 The dynamic.yml patch is deployed to `/opt/docker/traefik/config/dynamic.yml` on nullstone (hot-reloaded via Traefik file provider). Backup of the pre-fix file kept at `/opt/docker/traefik/config/dynamic.yml.bak.pre-sw-fix-1778291088` for one-step rollback if needed. Traefik config is intentionally NOT mirrored into the arrflix-repo (lives in nullstone-side `/opt/docker/traefik/`); the doc captures the change in full.
+
+---
+
+## Headless comparison (2026-05-09 ~02:57Z)
+
+Followup empirical test using Playwright + chromium-headless against both
+sides simultaneously. Script at `bin/prod-vs-dev-compare.py`.
+
+### Method
+- Login as admin on each side (`s8n/2001dude` on prod; `test/2001dude` on dev,
+  reset via `UPDATE Users SET Password=NULL WHERE Username='test'` while the
+  container was stopped, then API-set to `2001dude`).
+- Navigate to `Mike Nolan Show — S01E04 (Ding Dong Delli)`,
+  ItemId `9312799ca24979bd05aad9733ce7ee14` (same on both sides — guid is
+  derived from the file path which is identical).
+- Click the on-page Play button, sample state at t=5/10/20/30s. At each
+  sample: `<video>.{currentTime,paused,error,videoWidth,readyState}` plus
+  a 32×18 `drawImage(<video>)` to a hidden canvas to compute average luma
+  (so we can tell if the video element itself is decoding pixels), plus
+  `document.elementsFromPoint(videoCenter)` to record the DOM stacking
+  order at the centre of the `<video>` element.
+
+### File metadata (identical on both sides)
+
+| Field        | Value                                                                |
+|--------------|----------------------------------------------------------------------|
+| Path         | `/media/tv/The Mike Nolan Show (2016)/Season 01/...S01E04 - Ding Dong Delli.mkv` |
+| Container    | `mkv`                                                                |
+| Size         | `11534336` bytes (~11 MB)                                            |
+| Bitrate      | `473009` bps                                                         |
+| Video codec  | `h264 High@4.0`, SDR, 1920×1080                                      |
+| Audio codec  | `aac LC`, 2-channel                                                  |
+
+### PlaybackInfo / API
+
+Identical on both sides for the API-issued `POST /Items/{id}/PlaybackInfo`:
+
+| Field                  | prod        | dev         |
+|------------------------|-------------|-------------|
+| Container              | `mkv`       | `mkv`       |
+| Protocol               | `File`      | `File`      |
+| SupportsDirectPlay     | `True`      | `True`      |
+| SupportsDirectStream   | `True`      | `True`      |
+| TranscodingUrl         | `None`      | `None`      |
+| TranscodeReasons       | `None`      | `None`      |
+| Bitrate                | `473009`    | `473009`    |
+
+So the server's playback decision is **identical** — it's not a
+transcoder-vs-direct-play divergence. No ffmpeg cmdline appeared in either
+container's `docker logs` during the run; both DirectPlay'd the .mkv.
+
+### Stream URL (decoded)
+- **prod**: `https://arrflix.s8n.ru/Videos/9312799ca24979bd05aad9733ce7ee14/stream.mkv?Static=true&mediaSourceId=9312799ca24979bd05aad9733ce7ee14&deviceId=...&api_key=...&Tag=448d71aa9830b270dc375a83a4d6c6fc#t=70.44175`
+- **dev**:  `https://dev.arrflix.s8n.ru/Videos/9312799ca24979bd05aad9733ce7ee14/stream.mkv?Static=true&mediaSourceId=9312799ca24979bd05aad9733ce7ee14&deviceId=...&api_key=...&Tag=448d71aa9830b270dc375a83a4d6c6fc#t=29.892814`
+
+Same URL template, same file Tag (`448d71aa9830b270dc375a83a4d6c6fc`), same
+DirectPlay path. The `#t=` fragment difference is just resume-position state.
+
+### Final video state at t=30s
+
+| Field         | prod                        | dev                         |
+|---------------|-----------------------------|-----------------------------|
+| currentTime   | `99.68`                     | `60.19`                     |
+| duration      | `328.368`                   | `328.368`                   |
+| paused        | `False`                     | `False`                     |
+| error         | `None`                      | `None`                      |
+| videoWidth    | `1920`                      | `1920`                      |
+| videoHeight   | `1080`                      | `1080`                      |
+| readyState    | `4` (HAVE_ENOUGH_DATA)      | `4`                         |
+| paintLuma     | `107.2` (real frame data)   | `129.7`                     |
+| paintOk       | `True`                      | `True`                      |
+
+The `<video>` element on prod **is decoding actual pixels** — `drawImage(v)`
+captures luma >100 (vivid cartoon color). Yet a full-page screenshot at the
+same instant is **all-black**. The pixels never reach the page composition.
+
+### Smoking gun — DOM stacking at the video centre
+
+```
+=== prod ===
+[top]  div#videoOsdPage.page libraryPage mainAnimatedPage
+       bg=rgb(0, 0, 0)         ← OPAQUE BLACK, full viewport
+       z=auto, position=absolute
+       div.backgroundContainer backgroundContainer-transparent  bg=rgba(0,0,0,0)
+       video.htmlvideoplayer   bg=rgba(0,0,0,0)
+       div.videoPlayerContainer  bg=rgb(0,0,0)
+[bot]  body, html
+
+=== dev ===
+[top]  div#videoOsdPage.page libraryPage mainAnimatedPage
+       bg=rgba(0, 0, 0, 0)    ← TRANSPARENT
+       z=auto, position=absolute
+       div.backgroundContainer backgroundContainer-transparent  bg=rgba(0,0,0,0)
+       video.htmlvideoplayer   bg=rgba(0,0,0,0)
+       div.videoPlayerContainer  bg=rgb(0,0,0)
+[bot]  body, html
+```
+
+`#videoOsdPage` has the **same class names** on both sides
+(`page libraryPage mainAnimatedPage`), the same DOM position, the same
+z-index/position. The only difference is `background-color`: `rgb(0,0,0)`
+on prod versus `rgba(0,0,0,0)` on dev. That single property covers the
+entire viewport with opaque black on top of the still-decoding video.
+
+### Root cause — Custom CSS in `branding.xml`
+
+`/home/docker/jellyfin/config/config/branding.xml` (prod) is 401 lines.
+`/home/docker/jellyfin-dev/config/config/branding.xml` is 116 lines. The
+diff includes the `BLACK-PASS 2026-05-08` rule that doesn't exist on dev:
+
+```css
+/* === BLACK-PASS 2026-05-08 — eliminate ALL residual grays ... === */
+:root { --theme-background-color: #000000 !important; ... }
+...
+/* Page-container surfaces — hit every wrapper the SPA might render */
+.dashboardDocument, body.dashboardDocument,
+.mainAnimatedPages, .pageContainer, .libraryPage,
+.absolutePageTabContent, .itemDetailPage,
+.padded-bottom-page, #mainDrawerPanel, #mainPanel,
+.layout-desktop, .layout-mobile, .layout-tv {
+  background-color: #000000 !important;       /* ← THIS LINE */
+}
+```
+
+Later in the same file there's a guarded undo:
+
+```css
+.libraryPage:has(.itemDetailPage),
+.absolutePageTabContent:has(.itemDetailPage) {
+  background-color: transparent !important;
+  background: transparent !important;
+}
+```
+
+The undo only matches when the `.libraryPage` contains `.itemDetailPage`
+as a descendant. The OSD/video page `#videoOsdPage` also has class
+`libraryPage`, but its descendant tree is the video player (`.htmlVideoPlayer`,
+`.videoOsdBottom`, etc.) — **not** `.itemDetailPage`. So the BLACK-PASS rule
+wins for the OSD page and paints opaque black over the playing video.
+
+### Fix
+
+Extend the override to also exempt `.libraryPage` instances that contain
+the video player. In `/home/docker/jellyfin/config/config/branding.xml`,
+in the `.libraryPage:has(.itemDetailPage)` block, add:
+
+```css
+.libraryPage:has(.itemDetailPage),
+.libraryPage:has(.htmlVideoPlayer),     /* ← add this */
+.libraryPage:has(.videoPlayerContainer), /* ← and this */
+.libraryPage#videoOsdPage,               /* ← belt + suspenders */
+.absolutePageTabContent:has(.itemDetailPage) {
+  background-color: transparent !important;
+  background: transparent !important;
+}
+```
+
+Or, more surgically, add a single rule:
+
+```css
+#videoOsdPage,
+.page#videoOsdPage,
+.libraryPage#videoOsdPage {
+  background-color: transparent !important;
+  background: transparent !important;
+}
+```
+
+Either form will let the underlying `<video>` element show through the OSD
+page wrapper while playback is active. No server / Traefik / Jellyfin-image
+change is needed; just edit `branding.xml` (Custom CSS) and the change takes
+effect on next hard reload of the web client.
+
+### One-line answer
+
+**prod fails because the `BLACK-PASS 2026-05-08` Custom-CSS rule paints
+`#videoOsdPage` (which has class `libraryPage`) with `background:#000 !important`,
+covering the still-decoding `<video>` element with an opaque black div whenever
+the OSD page is rendered for playback. Dev never shipped that rule, so its
+`#videoOsdPage` stays transparent and the video paints through.**
+
+### Artifacts
+
+- `bin/prod-vs-dev-compare.py` — the comparison script (committable)
+- `/tmp/arrflix-prod-vs-dev/diff.json` and `/tmp/arrflix-prod-vs-dev/diff.md`
+- `/tmp/arrflix-prod-vs-dev/{prod,dev}/result.json` — full per-side JSON
+  (includes every `/Videos /Items /master.m3u8 /PlaybackInfo /Audio /stream`
+  request URL + status, browser console, server log tail)
+- `/tmp/arrflix-prod-vs-dev/{prod,dev}/play-t{5,10,20,30}.png` — screenshots
+- API key `arrflix-prodvsdev-2026-05-09` was created on each side at run
+  start and deleted at run end (404 on the dev cleanup is benign — the new
+  key is no longer in the listing because token rotation already invalidated
+  it after `Auth/Keys` operation; manual confirmation via
+  `curl https://{prod,dev}.../Auth/Keys` shows no leftover entry).
+
+Note that the test harness ran in headless chromium and was on prod still
+**painting actual pixels** to the underlying `<video>` element (paintLuma
+~107). On a real browser the same overlay div fully covers the canvas, so
+the user reports "black screen" exactly as observed in the screenshots.
+
+---
+
+## INC7 final — CSS overlay was the actual cause
+
+After INC7-attempt-1 (Traefik SW-pin fix) shipped, headless playwright
+on prod still measured **`darkPct=100%`** of the visual viewport while
+`<video>` element decoded frames (canvas `drawImage` luma=84,
+`videoWidth=1920`, `currentTime` advancing). Confirmed agent 2's
+hypothesis: `<video>` paints, but a CSS overlay covers it.
+
+### Root cause
+
+`branding.xml` BLACK-PASS rule paints `.libraryPage` with
+`background:#000 !important`. Jellyfin's video OSD page renders as
+`<div id="videoOsdPage" class="libraryPage">` (id + class).
+The class match → opaque black div ABOVE the `<video>` element →
+visually black despite real frames decoding underneath.
+
+Dev didn't ship the BLACK-PASS block at all → no overlay → video
+visible.
+
+### Fix (CSS, server-side branding.xml CustomCss)
+
+```css
+.libraryPage:has(.htmlVideoPlayer),
+.libraryPage#videoOsdPage,
+#videoOsdPage,
+#videoOsdPage .pageContainer,
+#videoOsdPage .layout-desktop,
+#videoOsdPage .mainAnimatedPages {
+  background-color: transparent !important;
+  background: transparent !important;
+}
+```
+
+### Verified
+
+Post-fix headless playwright: `darkPct=9.8%`. Screenshot `/tmp/inc7-after.png`
+shows actual MNS S1E4 video frame (sasquatch in cage). Real visual paint.
+
+### Cleanup
+
+- Removed `clear-cache-only@file` middleware attachment from
+  `jellyfin-html-nocache` router. INC7 SW-pin fix + INC7 CSS fix
+  together close the case; the temporary cache-wipe middleware is no
+  longer needed and would burn HTTP cache on every visit.
+- Backup: `/opt/docker/traefik/config/dynamic.yml.bak.inc6-removal.*`
+
+### Lesson
+
+Agent 6 marked "verified" using video-element state alone (currentTime
+advancing, readyState=4, videoWidth>0). Element decoded fine — but
+CSS overlay above it made it visually black. Headless test must
+ALSO sample pixel histogram + canvas drawImage on the actual painted
+viewport, not just element properties.
+
+`bin/headless-test-v2.py` already includes the canvas-drawImage paint
+check (Pillow + drawImage luma). Add a `darkPct` assertion to surface
+this class of regression next time.
+
+### Status
+
+INC7 FINAL — case closed. Owner action: hard-reload browser,
+confirm visual paint.