test: close the last coverage debt the roadmap still listed

- `overflow-clip` gets a safelist anchor in index.css (its only occurrence is a `.ts` constant),
  and the chip-lane contract keeps it there.
- PlexPlayer's Backspace ownership rule is pinned on all three branches: nothing above, a foreign
  layer above (it defers), and its own panel open under a layer (it still closes the panel).
- Removing a playlist item bumps the list's `updated_at`, like the three other item-only writes.
- Seen in a real browser on localdev: an exhausted comfort-shelf tile (an empty pinned playlist) is
  focusable, aria-disabled, and its Shift+F10 menu offers Play off and Remove from shelf.

frontend/src/index.css

@@ -6,6 +6,12 @@
    consumer today). Keeps the semantic token set complete + future-proof. */
 @source inline("text-danger-fg text-warn-fg text-success-fg text-info-fg");
 
+/* `overflow-clip` lives in exactly one place, a `.ts` constant (lib/useChipOverflowFit.ts). If source
+   detection ever stopped covering that file the utility would silently leave the bundle and the
+   1024px sideways-scroll bug on the chip lanes would come back with every lane green — so it is
+   anchored here too. */
+@source inline("overflow-clip");
+
 /* `inline` is load-bearing: the color vars (--bg/--accent/… below) are redefined at
    runtime per html[data-scheme]/[data-theme], so utilities must inline the value and
    resolve it at the USE site, not reference a once-computed --color-* token. This also
@@ -571,9 +577,9 @@ body {
     background-color: var(--warn);
     color: var(--warn-fg);
   }
-  .btn-primary:hover:not(:disabled),
-  .btn-danger:hover:not(:disabled),
-  .btn-warn:hover:not(:disabled) {
+  .btn-primary:hover:not(:disabled):not([aria-disabled="true"]),
+  .btn-danger:hover:not(:disabled):not([aria-disabled="true"]),
+  .btn-warn:hover:not(:disabled):not([aria-disabled="true"]) {
     opacity: 0.9;
   }
 
@@ -615,8 +621,10 @@ body {
 }
 /* `:not(:disabled)` for the same reason ui/Button prefixes every variant hover with `enabled:` — a
    disabled control must not advertise a click that does nothing. The Tailwind half was gated in E10
-   review round 1 and this half was missed, so a disabled glass button still lifted (round 2). */
-.glass-hover:not(:disabled):hover {
+   review round 1 and this half was missed, so a disabled glass button still lifted (round 2).
+   `:not([aria-disabled="true"])` too: a FocusSafeButton that holds the focus is disabled by
+   aria-disabled, not the native attribute (debt burn 2026-09), and lifted again until this. */
+.glass-hover:not(:disabled):not([aria-disabled="true"]):hover {
   border-color: color-mix(in srgb, var(--accent) 55%, transparent);
   box-shadow:
     inset 0 1px 0 color-mix(in srgb, #fff 12%, transparent),