keyboard: the one-Esc law — a surfaced layer claims at the document level (keyboard 4 of 4)

Owner ruling (keyboard round 2026-10-06): Esc (or any key) does ONE
action, on the topmost active layer. The plan-open-while-dictating
double-act was the symptom: the plan popup listened at WINDOW level
with no claim, and same-node window listeners all fire — the global
chain (registered first) cancelled the dictation while the plan's own
listener closed the plan. One Esc, two actions.

The law (now the house pattern, documented at the chain):
- field-level handlers claim at their element (focus in a field: the
  field's action) — unchanged, already correct
- every SURFACED layer claims at the DOCUMENT level with preventDefault
  + stopPropagation — document fires before the window chain, so the
  chain stays silent under any surface
- the window chain is the bottom-up fallback: dictation (a live capture,
  NOT a surface — it survives the Esc that closes a plan or overlay),
  then abort (escAbortTarget layers its own targets)

Converted to the claim: plan popup, session overlay, chain table,
settings dialog, setup dialog, the delete/abort dialogs (window-level
stopPropagation was never enough — same-node listeners all fire), and
the stats popover. Popovers (popover-dismiss), menus, model picker, and
the sidebar context menu already claimed correctly.

1427 tests, tsc, lint, build green.

components/keyboard-shortcuts.tsx

@@ -82,10 +82,18 @@ export function KeyboardShortcuts() {
 					e.preventDefault();
 					return;
 				}
-				// Popovers stopPropagation on their own Esc, so reaching here
-				// means none was open. Dictation first, then abort the turn
-				// (a server-side turn has no client request to abort — the
-				// abort seam in Chat decides what's honestly stoppable).
+				// THE ONE-ESC LAW (owner, keyboard round 2026-10-06): one
+				// Esc, one action, on the topmost active layer. Field-level
+				// handlers claim at their element (focus in a field: the
+				// field's action); every SURFACED layer (popovers, plan,
+				// overlays, dialogs) claims at the DOCUMENT level, which
+				// fires before this window listener — so reaching here means
+				// NOTHING is surfaced and no field is focused. This chain is
+				// the fallback, bottom-up: dictation (a live capture, not a
+				// surface — it survives Esc that closes a plan or overlay),
+				// then abort the turn (a server-side turn has no client
+				// request to abort — the abort seam in Chat decides what's
+				// honestly stoppable, layered by escAbortTarget).
 				if (isDictationActive()) {
 					e.preventDefault();
 					window.dispatchEvent(new CustomEvent("lh:kbd-cancel-dictation"));