Sixth step of the Compose-backed architecture (#18–#22). Restores real navigation and adds the presentation surface — including alert, which the classic-view renderer had no path to at all.

Navigation

Swift owns the stack. NavigationStack holds a NavigationModel persisted by identity path; links push, @Environment(\.dismiss) pops, navigationDestination(for:) resolves value pushes, navigationTitle records per-screen titles. The stack emits every screen (root + pushed) as children, so the interpreter can animate between them with AnimatedContent and render the outgoing screen from cache during a pop. Scaffold + TopAppBar gives the title and a back arrow; system back flows through the same pop callback.

Presentation

• Sheet: .sheet(isPresented:) rides as a hidden child shown while the flag is true; the interpreter presents it as a ModalBottomSheet. Drag-to-dismiss and the dismiss action write the flag back, so Swift stays authoritative. presentationDetents supported.
• Alert: .alert(_:isPresented:message:buttons:) → Material 3 AlertDialog. New API — no Alert type existed under the old architecture.
• The normal child loop skips these hidden presentation nodes so they never render inline.

Tabs

TabView(selection:) with .tabItem and .tag; the interpreter renders a NavigationBar and shows the tagged tab. Selection is a @State binding, so both a tab tap and programmatic selection work.

Core additions

• @Environment gains the keyPath form (\.dismiss) alongside object injection, both through the same reflection seam.
• StateStorage.persistentObject(at:) holds container reference state (the nav stack) that must survive re-evaluation without living in a view's @State.
• The evaluator now installs state and injects environment for primitives (so containers hold state), handles _ResolutionEffectView wrappers (title/destination registration), and threads a per-screen title/detent sink.

Verification

• swift test: 24 tests — classic push, value push through navigationDestination, dismiss-pops, sheet presentation, tab selection.
• Emulator, full journeys:
  • Gallery renders as a NavigationStack ("Gallery" app bar, 10 links); tapping a row pushes with a back arrow; back pops.
  • Value-based navigation: Navigation → Push value 1 → "Value 1" screen resolved via navigationDestination, with its own title, and a further "Push value 2" link — the deepest path (a pushed screen registering a destination and pushing onto the same Swift-owned stack).
  • Sheet presents as a bottom modal and dismisses via @Environment(\.dismiss).
  • Alert shows title/message/OK/Cancel.
  • Tabs: bottom bar One/Two/Three; the "Select third tab" button drives @State and switches to Third tab.