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.

docs/keyboard.md

@@ -47,8 +47,10 @@ second pillar of input).
 | Cycle thinking level | Shift+Tab | `lh:kbd-cycle-thinking` (model-picker.tsx) |
 | Toggle sidebar | ⌘B | `lh:toggle-sidebar` (sidebar.tsx) |
 | Sessions search | ⌘⇧F | `lh:kbd-sessions-search` (sidebar.tsx) |
-| Cycle session | ⌥↑ / ⌥↓ | `lh:kbd-cycle-session-prev/next` (sidebar.tsx) |
-| Open selected session | ⌥Enter | `lh:kbd-open-session` (sidebar.tsx) |
+| Walk search results | ↑ / ↓ *in the search field* | sidebar.tsx (cycles the filtered rows, wraps) |
+| Open search result | Enter *in the search field* | sidebar.tsx (walked row, else the first match) |
+| ~~Cycle session~~ | ~~⌥↑ / ⌥↓~~ | RETIRED (owner, 2026-10-10) — the search walk above replaces it |
+| ~~Open selected session~~ | ~~⌥Enter~~ | RETIRED (owner, 2026-10-10) — the search Enter above replaces it |
 | Jump to graph (home) | ⌘G | router.push in keyboard-shortcuts.tsx |
 | New session | ⌘N | router.push in keyboard-shortcuts.tsx |
 | Rename session | F2 | `lh:kbd-rename-session` (chat.tsx) |
@@ -57,6 +59,9 @@ second pillar of input).
 
 ## Model menu keyboard machine (owner polish, 2026-09-17)
 
+(Removed from the settings/cheat-sheet registry 2026-10-10 — obvious
+in-field navigation; the behavior below is unchanged.)
+
 While the model menu is open, focus stays in the search field and the
 menu owns ↑/↓/Enter inside the input's own handler: