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/keyboard-toggle-sidebar.test.ts

@@ -5,6 +5,7 @@ import {
 	bindingForAction,
 	formatBinding,
 	kbdEventForAction,
+	KEYBOARD_ACTIONS,
 } from "../src/core/keyboard.ts";
 import { kbdEventForAction as kbdEventForActionFromUi } from "../components/keyboard-shortcuts.tsx";
 
@@ -54,4 +55,21 @@ describe("the thinking pill suffix — ⇧⇥ via the registry", () => {
 		assert.equal(actionForBinding("shift+tab"), "cycle-thinking");
 		assert.equal(formatBinding("shift+tab"), "⇧⇥");
 	});
+});
+
+describe("the Alt session cycle is RETIRED (owner, 2026-10-10)", () => {
+	// Barely used, felt laggy — session navigation lives IN the search
+	// now (↑/↓ walk the filtered list, Enter opens; sidebar.tsx).
+	it("⌥↑ / ⌥↓ / ⌥↵ bind to NOTHING — no stray action fires", () => {
+		assert.equal(actionForBinding("alt+arrowup") ?? null, null);
+		assert.equal(actionForBinding("alt+arrowdown") ?? null, null);
+		assert.equal(actionForBinding("alt+enter") ?? null, null);
+	});
+
+	it("the actions are gone from the table (cheat sheet + settings render the registry)", () => {
+		const ids = KEYBOARD_ACTIONS.map((a) => a.id as string);
+		assert.ok(!ids.includes("cycle-session-prev"));
+		assert.ok(!ids.includes("cycle-session-next"));
+		assert.ok(!ids.includes("open-session"));
+	});
 });