ui: plan canvas ink extent + the keyboard-first round

Plan canvas (owner report: arrows clipped at the viewBox edge in dist —
measured 14px/20px cuts in the owner's real plans): blockLayout now
unions node boxes with every edge path's control-point hull (a bezier
never leaves it; the layout calls edgePathD with the renderer's exact
inputs). Dagre's node extent stays the floor, so ordinary plans render
byte-identical; the viewBox origin shifts only when ink bulges past
zero. Verified on both real chats; pins use the owner's real
linear-algebra tree (golden-real-data).

Keyboard-first (owner's law: Enter always submits, arrows always cycle;
text fields the only exception):
- Enter guard split (enter-submits): a focused BUTTON keeps native
  Enter only when keyboard-walked (:focus-visible) or inside an open
  overlay (menus/dialogs); pointer-clicked transcript buttons submit,
  preventDefault suppressing the re-activation underneath.
- Focus hygiene (focus-hygiene): pointer clicks on transient controls
  (agent/user thinking toggles, copy, mermaid expand, plan chip) blur
  to body — the state clicking empty space produces.
- Session search owns the walk: Up/Down wrap-cycle the filtered rows,
  Enter opens the walked row or the first match (quick-open), then
  blurs and keeps the query. The Alt-arrow session cycle is RETIRED.
- Registry: model-menu walk/pick entries removed (obvious in-field
  navigation, not settings material); question-dock keys stay
  displayOnly per owner ruling.

Gates: 1489/1489, typecheck, lint. Verified live end-to-end.

tests/render-settings.test.tsx

@@ -274,6 +274,10 @@ describe("KeyboardSection (thin SSR)", () => {
 		const html = renderToStaticMarkup(<KeyboardSection />);
 		assert.ok(html.includes("Fixed — part of this screen"));
 		assert.ok(!html.includes(`data-testid="kbd-rebind-question-next-row"`), "surface keys stay put");
-		assert.ok(!html.includes(`data-testid="kbd-rebind-model-menu-pick"`));
+		// The model-menu entries are GONE entirely (owner, 2026-10-10):
+		// obvious in-field navigation, not settings material.
+		assert.ok(!html.includes("Model menu"), "model-menu rows removed");
+		assert.ok(!KEYBOARD_ACTIONS.some((a) => a.id as string === "model-menu-walk"));
+		assert.ok(!KEYBOARD_ACTIONS.some((a) => a.id as string === "model-menu-pick"));
 	});
 });