A fork carries a checkpoint from its source run, but its first
run.created event contains only a sandbox plan. Resume previously tried
to reconnect that planned sandbox and failed because no instance
exists. Now a fork resume with a Planned sandbox record builds a fresh
sandbox instead; later fork resumes still reconnect the ready instance,
and a same-run resume with an uninitialized sandbox still fails the
precondition check.
Also consolidates the test module's three near-identical InitOptions
literals into a shared test_init_options helper.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>