opentui(phase3): launcher integration — HERMES_TUI_ENGINE dual-engine

hermes --tui launches the native OpenTUI engine (Bun) when
HERMES_TUI_ENGINE=opentui (env) or display.tui_engine=opentui (config);
Ink stays the default and the shipping path is untouched.

- _resolve_tui_engine() (env > config > ink); refuses opentui on
  Windows/Termux (no Bun) -> falls back to ink with a notice.
- _make_opentui_argv() -> [bun, src/entry.real.tsx] (no build step).
- _bun_bin() with HERMES_BUN override.
- Branch at top of _make_tui_argv BEFORE _ensure_tui_node (Bun-only host
  must not bootstrap Node).
- Gate _launch_tui NODE_OPTIONS/--max-old-space-size on engine==ink (Bun
  is JSC; the V8 flag errors/ignores).

Verified end-to-end via tmux: real hermes --tui -> Bun -> OpenTUI ->
real Python gateway streamed a real reply. No-flag default still ink.

apps/desktop/src/app/session/hooks/use-session-state-cache.test.tsx

@@ -2,20 +2,7 @@ import { act, cleanup, render } from '@testing-library/react'
 import type { MutableRefObject } from 'react'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 
-import {
-  $currentFastMode,
-  $currentModel,
-  $currentProvider,
-  $currentReasoningEffort,
-  $currentServiceTier,
-  $turnStartedAt,
-  setCurrentFastMode,
-  setCurrentModel,
-  setCurrentProvider,
-  setCurrentReasoningEffort,
-  setCurrentServiceTier,
-  setTurnStartedAt
-} from '@/store/session'
+import { $turnStartedAt, setTurnStartedAt } from '@/store/session'
 
 import { useSessionStateCache } from './use-session-state-cache'
 
@@ -59,22 +46,12 @@ describe('useSessionStateCache — per-session turn timer', () => {
       return null as unknown as number
     })
     setTurnStartedAt(null)
-    setCurrentModel('')
-    setCurrentProvider('')
-    setCurrentReasoningEffort('')
-    setCurrentServiceTier('')
-    setCurrentFastMode(false)
   })
 
   afterEach(() => {
     cleanup()
     vi.restoreAllMocks()
     setTurnStartedAt(null)
-    setCurrentModel('')
-    setCurrentProvider('')
-    setCurrentReasoningEffort('')
-    setCurrentServiceTier('')
-    setCurrentFastMode(false)
   })
 
   it("keeps a background session's running turn clock and never mirrors it to the view", () => {
@@ -138,78 +115,4 @@ describe('useSessionStateCache — per-session turn timer', () => {
     })
     expect($turnStartedAt.get()).toBeNull()
   })
-
-  it('mirrors the focused session model metadata when switching from a cached session', () => {
-    let cache!: Cache
-    const { rerender } = render(
-      <Harness activeSessionId="fg-runtime" onReady={c => (cache = c)} selectedStoredSessionId="fg-stored" />
-    )
-
-    act(() => {
-      cache.updateSessionState(
-        'bg-runtime',
-        state => ({
-          ...state,
-          fast: true,
-          model: 'anthropic/claude-opus-4.8',
-          provider: 'anthropic',
-          reasoningEffort: 'high',
-          serviceTier: 'priority'
-        }),
-        'bg-stored'
-      )
-    })
-
-    // Background metadata is cached but must not bleed into the visible statusbar.
-    expect($currentModel.get()).toBe('')
-    expect($currentReasoningEffort.get()).toBe('')
-    expect($currentFastMode.get()).toBe(false)
-
-    rerender(<Harness activeSessionId="bg-runtime" onReady={c => (cache = c)} selectedStoredSessionId="bg-stored" />)
-
-    const bgState = cache.sessionStateByRuntimeIdRef.current.get('bg-runtime')
-    expect(bgState).toBeTruthy()
-
-    act(() => {
-      cache.syncSessionStateToView('bg-runtime', bgState!)
-    })
-
-    expect($currentModel.get()).toBe('anthropic/claude-opus-4.8')
-    expect($currentProvider.get()).toBe('anthropic')
-    expect($currentReasoningEffort.get()).toBe('high')
-    expect($currentServiceTier.get()).toBe('priority')
-    expect($currentFastMode.get()).toBe(true)
-  })
-
-  it('clears stale model metadata when the newly focused session has no cached value', () => {
-    setCurrentModel('previous-model')
-    setCurrentProvider('previous-provider')
-    setCurrentReasoningEffort('high')
-    setCurrentServiceTier('priority')
-    setCurrentFastMode(true)
-
-    let cache!: Cache
-    const { rerender } = render(
-      <Harness activeSessionId="fg-runtime" onReady={c => (cache = c)} selectedStoredSessionId="fg-stored" />
-    )
-
-    act(() => {
-      cache.updateSessionState('bg-runtime', state => ({ ...state }), 'bg-stored')
-    })
-
-    rerender(<Harness activeSessionId="bg-runtime" onReady={c => (cache = c)} selectedStoredSessionId="bg-stored" />)
-
-    const bgState = cache.sessionStateByRuntimeIdRef.current.get('bg-runtime')
-    expect(bgState).toBeTruthy()
-
-    act(() => {
-      cache.syncSessionStateToView('bg-runtime', bgState!)
-    })
-
-    expect($currentModel.get()).toBe('')
-    expect($currentProvider.get()).toBe('')
-    expect($currentReasoningEffort.get()).toBe('')
-    expect($currentServiceTier.get()).toBe('')
-    expect($currentFastMode.get()).toBe(false)
-  })
 })