fix: keep forked Codex threads subscribed

[ladydd]

Closes LodyAI/Lody#543

Problem / pressure

thread/fork returns a live child thread. The adapter then called threadUnsubscribe on that child. runTurn waits for turn/completed notifications, so the first prompt on a Fork session never finishes. Codex can complete the turn on the server; the adapter never sees it. Stop reports no active turn to interrupt. The next prompt is A Codex prompt is already active. The parent session still works.

onSubscribed is only a lifecycle callback. It does not subscribe. This is not Codex thread/fork failing.

Summary

Keep the child subscribed when fork install succeeds. Unsubscribe only if assignProject fails before the session is returned. closeSession still unsubscribes.

Visual explanation

sequenceDiagram
  participant Host
  participant Adapter
  participant Codex
  Host->>Adapter: session/fork
  Adapter->>Codex: thread/fork
  Codex-->>Adapter: child id (subscribed)
  Note over Adapter: before: threadUnsubscribe(child)
  Host->>Adapter: session/prompt
  Adapter->>Codex: turn/start
  Codex-->>Adapter: turn/start ok
  Codex-->>Adapter: turn/completed (needs subscription)
  Note over Adapter: after: stay subscribed so completed arrives

Loading

Before / after

Before	After
Fork tab hangs on first prompt; stop then already active	Child stays subscribed; first prompt can complete
Parent still answers	Unchanged

Test plan

• vitest run src/__tests__/CodexACPAgent/session-fork.test.ts --no-file-parallelism --retry=0 — 3 passed (successful fork does not unsubscribe; install failure still unsubscribes).
• vitest run src/__tests__/CodexACPAgent/CodexAcpClient.test.ts -t 'forks an ACP session through thread/fork' — passed.
• Independent app-server check (Codex 0.153.4, synthetic model): suppressing that unsubscribe let the child finish two turns with turn/completed. This PR is that change plus failure-path cleanup. Live Electron E2E forks a session and continues was not re-run here (RUN_E2E_TESTS + API key).

Context

Authored with an AI coding agent. Reviewers should challenge: leaving the child subscribed vs any reason the old tests required unsubscribe; whether assignProject failure is the only install-fail path that must unsubscribe.

Lody still needs a submodule bump after this merge.

[Leeeon233]

thanks