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Architecture

CoreJ2 isolates SwiftUI from FreeJ2ME. All launches cross a bridge so the vendor emulator can evolve with minimal forks.

Layer stack

SwiftUI
  ↓
Bridge
  ↓
Runtime Host
  ↓
Embedded OpenJDK Mobile
  ↓
FreeJ2ME
  ↓
Commercial MIDlet

flowchart TB
  subgraph presentation [Presentation]
    UI[SwiftUI]
  end
  subgraph application [Application]
    Bridge[Bridge]
    Host[Runtime Host]
  end
  subgraph runtime [Embedded runtime]
    JVM[Embedded OpenJDK Mobile]
    FJ[FreeJ2ME]
    Mid[Commercial MIDlet]
  end
  UI --> Bridge --> Host --> JVM --> FJ --> Mid

Ownership and responsibilities

Layer Owns Must not
SwiftUI Layout, chrome, keypad/touch gestures Call JNI or FreeJ2ME types
Bridge Launch/stop API for the app Embed FreeJ2ME classes
Runtime Host Map product models → bootstrap ops Leak JNIEnv upward
Embedded OpenJDK Mobile In-process Zero VM Be replaced by a desktop process on iOS
FreeJ2ME MIDP/CLDC + LCD Be patched except when a story requires a minimal fix
Commercial MIDlet Game code Escape the sandbox

Session lifecycle

stateDiagram-v2
  [*] --> Uninitialized
  Uninitialized --> Starting: initialize
  Starting --> Ready: platform + painter bound
  Ready --> Ready: runJar / frames
  Ready --> Shutdown: stopSession
  Shutdown --> Starting: initialize again same JVM
  Ready --> Shutdown: failed launch unwind

Epic 11 ensured failed launches always unwind via stopSession, so the host cannot stick in ready.