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.

components/thinking-block.tsx

@@ -2,6 +2,7 @@
 
 import { useEffect, useRef, useState } from "react";
 import { ChevronDownIcon } from "lucide-react";
+import { blurAfterPointerClick } from "@/components/focus-hygiene";
 import { cn } from "@/lib/utils";
 
 /** The unified user-thinking row (owner round, 2026-10-05): ONE visual
@@ -115,7 +116,10 @@ export function ThinkingBlock({
 			<button
 				type="button"
 				data-testid={testId ? `${testId}-trigger` : undefined}
-				onClick={() => setOpen((v) => !v)}
+				onClick={(e) => {
+					setOpen((v) => !v);
+					blurAfterPointerClick(e);
+				}}
 				aria-expanded={open}
 				className="flex w-full items-center gap-2 font-medium uppercase tracking-wide text-muted-foreground transition-colors hover:text-foreground"
 			>