// Starting or resuming the single Codex thread a structured session owns.
//
// The reply is verified before the caller registers the session, because a
// resume that lands on a different thread is a fork wearing a resume's name —
// recording it would make the durable handle chain lie about what this session
// actually proved.

import type { CodexAppServerConnection } from './codex-app-server-connection'
import { readCodexThreadId, readCodexThreadPath } from './codex-structured-thread-facts'

export type CodexOpenedThread = {
  threadId: string
  /** Rollout file Codex named, when it named one. */
  historyPath: string | null
}

export async function openCodexThread(
  connection: CodexAppServerConnection,
  launch: { cwd: string; resumeThreadId: string | null },
  timeoutMs: number | undefined
): Promise<CodexOpenedThread> {
  const opened = await connection.request(
    launch.resumeThreadId ? 'thread/resume' : 'thread/start',
    launch.resumeThreadId
      ? { threadId: launch.resumeThreadId, cwd: launch.cwd }
      : { cwd: launch.cwd },
    { timeoutMs }
  )
  const threadId = readCodexThreadId(opened)
  if (!threadId) {
    throw new Error('codex app-server did not name the thread it opened')
  }
  if (launch.resumeThreadId && threadId !== launch.resumeThreadId) {
    throw new Error(`codex app-server resumed ${threadId} instead of ${launch.resumeThreadId}`)
  }
  return { threadId, historyPath: readCodexThreadPath(opened) }
}