fix(diagnostics): deep-review round 4 — a claim only its owner may write, and a player that keeps the Tab

Round 4 was targeted at the surfaces rounds 2 and 3 changed. 29 findings raised,
26 survived deduplication, 12 survived three adversarial readings each.

`set_delivery` renewed the claim but never checked it was still ours, while its
sibling `release_send` always did. `expire_on_commit` is off, so the token it
re-stamped came from the caller's own memory, not the row: a send that outlived
its 600 s lease came back, overwrote the take-over send's committed links with a
full-column write, and put its own dead token back. It now takes the token, reads
the row's claim with a targeted scalar (not a refresh, which would discard the
`issue_url` assigned one line earlier) and raises `SendClaimLost` rather than
writing. An issue created by a send that had already lost its claim is logged with
its number — that record is the only one that will exist.

The tracker's settings are read above the pre-call checkpoint instead of inside
`_client`. Reading them there was a SELECT one line after the commit that was
meant to end the transaction, and held it — idle, snapshot pinned — across the
repository check and the create. The comment and the module docstring said
otherwise; measuring it in pg_stat_activity is what settled it. Two more comments
were saying things the code had stopped doing: the `**state` spread does not carry
the claim (`set_delivery` strips and re-stamps it), and react-query does not
debounce the preview — the editor being unmounted is what paces it.

The composer stopped stranding the focus on `<body>`: a send that creates the
issue and then fails on an attachment unmounts the button that was just pressed,
and only the success path handed the focus on. Export no longer saves into a
refusal it does not need — the zip is the way out of a stuck send, and its
pre-save was the one step that could not survive one. The delivery banner
announces through a role instead of an `aria-live` created with its own message.

`historyState` returns a union, so `chipTone` matching on the same keys is checked
by tsc rather than by hope.

PlexPlayer was the only full-screen overlay in the tree with no focus containment
at all — Tab walked out of an opaque player into a page nobody can see. It now
carries the shared trap. Closing that hole exposed the one underneath it:
`useDismiss` registered as a layer that traps the Tab while installing no trap,
so the player stood its own down for its own menus. Measured in a real browser:
30 Tabs with the settings panel open, 9 escapes into the nav rail, and 0 after.
Escape ordering is unchanged — the panel first, then the player.

Three tests that did not hold their line: the advisory lock's call site (deleting
it left the suite green), the trail assertion whose `all()` was vacuous over an
empty filter, and a `layerStack` assertion the stand-in dialog already forced.
All eleven executable fixes mutation-checked red for the right reason; the two
comment corrections have nothing to pin.

frontend/src/components/PlexPlayer.tsx

@@ -74,7 +74,14 @@ import { LS, useAccountPersistedObject } from "../lib/storage";
 import { useDismiss } from "../lib/useDismiss";
 import { useScrollFade } from "../lib/useScrollFade";
 import { useBackToClose } from "../lib/history";
-import { pushLayer, removeLayer, anyLayerAbove, escapeHandled } from "../lib/layerStack";
+import { trapTab } from "./ui/dialogFocus";
+import {
+  pushLayer,
+  removeLayer,
+  anyLayerAbove,
+  anyBlockingLayerAbove,
+  escapeHandled,
+} from "../lib/layerStack";
 
 // The rich info overlay (poster/cast/ratings) reuses the same component as the card's info page.
 const PlexInfo = lazy(() => import("./PlexInfo"));
@@ -896,6 +903,19 @@ export default function PlexPlayer({ itemId, onClose, queue }: Props) {
       // remote", and `dispatch` still lets Escape through from inside a field (the only key that
       // opts in), which is why this is a guard around `wake` rather than an early return.
       if (!isTypingTarget(e)) wake();
+      // The shared dialog Tab trap. This player paints an opaque full-viewport layer over the app,
+      // so Tab leaving it lands on a control nobody can see, where the ring is invisible and the
+      // next Enter fires something blind. Every other overlay in the tree traps (ui/Modal,
+      // PlayerModal, OnboardingWizard, Welcome); this one never did, and deep-review round 4 caught
+      // it when the recorder's step prompt — which docks in this player's toast host — handed its
+      // own trap to "the dialog below" and found none. Only while nothing that owns the keyboard is
+      // layered above: a Modal opened over the player traps for itself. `wake()` above has already
+      // revealed the control band, so the trap cannot leave focus on a faded-out button.
+      if (e.key === "Tab") {
+        if (layerIdRef.current != null && anyBlockingLayerAbove(layerIdRef.current)) return;
+        if (wrapRef.current) trapTab(e, wrapRef.current);
+        return;
+      }
       dispatch(e, "plexPlayer", {
         playPause: (ev) => {
           // Let Space activate a focused button/link natively (e.g. "Skip intro"); only toggle