perf: cut cold-start download 58% and startup heap 22% via measured chunk-graph fixes (#2742)

* fix(ui): update session-switch-resync test to current handleEvent/setSessionTodos signatures

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* perf(build): split Shiki grammars/themes, CodeMirror legacy modes, and @pierre/diffs into on-demand chunks

Merging @shikijs/langs into one manual vendor chunk made the first language
request download every grammar (7.4 MB raw / 1 MB gzip). Letting Rollup split
these packages per dynamically imported module downloads only the languages,
themes, and modes actually used — matching how the worker build already
behaves. @pierre/diffs is split the same way so its pure patch parser (used by
the eager tool renderer) no longer drags the Shiki-importing render stack into
the startup graph.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* perf(ui): restore lazy heavy views and stop eager settings-graph loading

- MainLayout: DiffView/FilesView/GitView/PlanView return to lazyWithChunkRecovery
  (they were silently made static in 2031e3b4 while their Suspense wrappers
  remained), keeping the CodeMirror and @pierre/diffs stacks out of startup.
- ContextPanel: same lazy treatment for its Diff/Files/Git/Plan/Walkthrough
  tabs, with null Suspense fallbacks.
- CommandPalette imported getSettingsNavIcon from SettingsView, statically
  pulling the entire settings surface (SkillsPage -> CodeMirrorEditor -> vim
  mode, theme registry -> @pierre/diffs) into the eager graph; the helper now
  lives in lib/settings/metadata.
- The windowed SettingsWindow mounts only after its first open: rendering the
  lazy component closed made React fetch the SettingsView chunk graph at
  startup.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* perf(ui): keep @pierre/diffs + Shiki out of the eager chat graph and defer diff worker warmup

- DiffWorkerProvider no longer statically imports @pierre/diffs/worker or the
  theme registry, and no longer spawns 3 workers plus a main-thread shared
  highlighter during mount. Pools are created on demand through a dynamic
  module load, warmed via requestIdleCallback after startup settles, and
  useWorkerPool notifies consumers when a pool becomes available.
- ToolPart's rich diff preview moves to lazily loaded ToolPartDiffPreview;
  the plain-text patch (PlainDiffFallback) renders while the chunk loads,
  mirroring the existing error fallback. Theme registration happens during
  render inside the lazy module so PatchDiff never renders unregistered ids.
- ChatInput mounts its lazy ToolOutputDialog only after the first attachment
  preview opens instead of fetching the dialog chunk on the draft screen.
- getMarkdownSyntaxVars moves to a pierre-free markdownSyntaxVars module so
  eager code-rendering consumers stop importing the registration module.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* perf(web): load ghostty-web and Nerd Fonts on first terminal use

- ghostty-web (638 KB raw JS + WASM VT) is dynamically imported when a
  terminal actually mounts; TerminalView stays eagerly importable for the
  bottom dock.
- The ~2 MB of CDN Nerd Fonts are no longer preloaded and force-loaded on
  every cold start. index.html exposes an idempotent
  __openchamberEnsureNerdFonts hook; TerminalViewport requests it on mount
  and waits up to 2s so a cached font is in place before the glyph atlas is
  built, while a cold CDN fetch never blocks the terminal. Runtimes without
  the hook (VS Code, mobile) resolve immediately, matching their existing
  fallback-font behavior.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

---------

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/components/terminal/TerminalViewport.tsx

@@ -1,5 +1,5 @@
 import React from 'react';
-import { FitAddon, Ghostty, Terminal as GhosttyTerminal } from 'ghostty-web';
+import type { FitAddon, Ghostty, Terminal as GhosttyTerminal } from 'ghostty-web';
 
 import { cn } from '@/lib/utils';
 import type { TerminalTheme } from '@/lib/terminalTheme';
@@ -15,8 +15,33 @@ import {
 } from '@/lib/terminalTouchSelection';
 import type { TerminalChunk } from '@/stores/useTerminalStore';
 
-let ghosttyPromise: Promise<Ghostty> | null = null;
-const loadGhostty = (): Promise<Ghostty> => ghosttyPromise ??= Ghostty.load();
+// ghostty-web (638 KB raw of JS + the WASM VT) loads on demand: TerminalView
+// stays eagerly importable for the bottom dock without pulling the emulator
+// into the startup graph before a terminal is actually mounted.
+type GhosttyModule = typeof import('ghostty-web');
+type GhosttyRuntime = { module: GhosttyModule; ghostty: Ghostty };
+let ghosttyRuntimePromise: Promise<GhosttyRuntime> | null = null;
+const loadGhostty = (): Promise<GhosttyRuntime> =>
+  ghosttyRuntimePromise ??= import('ghostty-web').then(async (module) => ({
+    module,
+    ghostty: await module.Ghostty.load(),
+  }));
+
+// The web entry defers its ~2 MB Nerd Font download until a terminal actually
+// mounts (see the `__openchamberEnsureNerdFonts` hook in index.html). Wait for
+// it with a short bound so a cached font is in place before the glyph atlas is
+// built, while a cold CDN fetch never blocks the terminal from opening; the
+// runtimes without the hook (VS Code, mobile) resolve immediately.
+const NERD_FONT_WAIT_MS = 2000;
+const ensureNerdFonts = (): Promise<void> => {
+  if (typeof window === 'undefined') return Promise.resolve();
+  const loader = (window as typeof window & { __openchamberEnsureNerdFonts?: () => Promise<void> }).__openchamberEnsureNerdFonts;
+  if (typeof loader !== 'function') return Promise.resolve();
+  return Promise.race([
+    Promise.resolve(loader()).catch(() => undefined),
+    new Promise<void>((resolve) => setTimeout(resolve, NERD_FONT_WAIT_MS)),
+  ]).then(() => undefined);
+};
 
 type TerminalSize = { cols: number; rows: number };
 
@@ -211,13 +236,13 @@ const TerminalViewport = React.forwardRef<TerminalController, Props>(({
     window.addEventListener('focus', handleWindowFocus);
     window.addEventListener('blur', handleWindowBlur);
 
-    loadGhostty().then((ghostty) => {
+    Promise.all([loadGhostty(), ensureNerdFonts()]).then(([{ module, ghostty }]) => {
       if (disposed) return;
-      terminal = new GhosttyTerminal({
+      terminal = new module.Terminal({
         ...getGhosttyTerminalOptions(fontFamily, fontSize, theme, ghostty, false),
         ...(provisionalSizeRef.current ?? {}),
       });
-      const fitAddon = new FitAddon();
+      const fitAddon = new module.FitAddon();
       terminal.loadAddon(fitAddon);
       terminal.open(container);
       terminalRef.current = terminal;