fix(diagnostics): deep-review round 2 — a send that claims, not one that blocks

The send no longer holds the session's row lock while it talks to the tracker:
it claims the session, gives the lock back, and checkpoints each step. A Stop
is never held behind a send, while a draft, a screenshot or a second send are
refused at once instead of queueing. The claim ages out, so a request that
died mid-send does not strand the session.

What the composer says is what happened: an attachment that went is no longer
named as one that did not (the missing body edit is its own line), and the
issue's screenshot count comes from the server when the list cannot be read,
so a failed read no longer blocks saving the draft. The zip is fetched as a
request, so its pace is a message and not a saved error page. Screenshots of a
finished report can be removed again; only one still being sent is held.

A recording's log elevation can no longer outlive it. The step prompt keeps
the keyboard (the page's keys stay quiet) and traps Tab itself. An image
pasted into a dialog opened over the composer stays that dialog's.

frontend/src/components/DebugRecorder.tsx

@@ -23,6 +23,7 @@ import { qk } from "../lib/queryKeys";
 import { dockUnderToasts } from "../lib/toastDock";
 import { useMe } from "../lib/useMe";
 import { Button } from "./ui/Button";
+import { trapTab } from "./ui/dialogFocus";
 import Modal from "./ui/Modal";
 import { LoadingState, StateMessage } from "./ui/QueryState";
 import SegmentedToggle from "./ui/SegmentedToggle";
@@ -286,14 +287,15 @@ function SettingsElapsed({ since }: { since: string }) {
 /** "What did you just do?" — optional; Enter marks the step, Escape leaves it unmarked. */
 function StepPrompt({ id, onDone }: { id: string; onDone: (label: string | null) => void }) {
   const { t } = useTranslation();
+  const box = useRef<HTMLDivElement>(null);
   const n = useStepCount(id) + 1;
   const label = useStepPrompt() ?? "";
   // A layer of its own, so Escape closes only the prompt — not the dialog or the player the pill may
-  // be sitting in: the topmost layer takes Escape (lib/layerStack), and this one opened last.
-  // Passive: it takes Escape, not the Tab — the dialog under it keeps its focus trap, which spans
-  // its toast host and so this prompt too; a blocking layer would switch that trap off and let Tab
-  // walk out of the dialog into the page behind its scrim.
-  useLayer(true, () => onDone(null), { passive: true });
+  // be sitting in: the topmost layer takes Escape (lib/layerStack), and this one opened last. It
+  // OWNS the keyboard while it is up (an autofocused field does), so the page's own keys stay quiet
+  // — and it therefore traps Tab itself, between its field and its button: a dialog under it defers
+  // its trap to the layer above, and without one of our own Tab walked out into the page behind.
+  useLayer(true, () => onDone(null));
   const onKeyDown = (e: ReactKeyboardEvent<HTMLInputElement>) => {
     if (e.key === "Enter") {
       e.preventDefault();
@@ -301,7 +303,13 @@ function StepPrompt({ id, onDone }: { id: string; onDone: (label: string | null)
     }
   };
   return (
-    <div className="absolute bottom-full left-0 mb-2 w-80 max-w-[calc(100vw-2rem)] glass rounded-xl p-3 flex flex-col gap-2 shadow-lg">
+    <div
+      ref={box}
+      onKeyDown={(e) => {
+        if (e.key === "Tab" && box.current) trapTab(e.nativeEvent, box.current);
+      }}
+      className="absolute bottom-full left-0 mb-2 w-80 max-w-[calc(100vw-2rem)] glass rounded-xl p-3 flex flex-col gap-2 shadow-lg"
+    >
       <label htmlFor="debug-step-label" className="text-sm text-muted">
         {t("recorder.pill.stepPrompt", { n })}
       </label>