* Move chat journal checkpoints off the host thread
* Apply checkpoint lifecycle style and teardown test checks
* Wake journal checkpoints for cleanup writes and retire fixture owners
* Use fixed time in attachment checkpoint fixture
* Derive checkpoint timer handles and check unref capability
* Preserve journal test close completion and event typing
* test: await journal close before fixture reuse and cleanup
* test: await registered journal fixture cleanup
* test: integrate goal sweep fixture with journal ownership
* Simplify journal checkpoint worker lifecycle