Add Mirror onCreated Callback Test · Entire

let's address the nit. discussion here go for it, then push

Bottom line: Added a focused unit test for the onCreated callback nit, verified, committed, and pushed to elegant-marinating-widget (PR #1587).

• New TestCreateAndAwaitMirror_OnCreated asserts the callback fires exactly once on CreateMirror success, before any polling/onStatus, and never on a create error — plus a no-wait case confirming no GetMirror poll.
• Extracted a mirrorsAPIPath test constant to satisfy goconst (the new occurrences tripped it).
• mise run fmt/lint clean; full unit suite passes (7443 tests).

The checkpoint-remote sync warning during push is unrelated (couldn't reach the checkpoint remote); the branch push itself succeeded.

Commit message:

test(mirror): cover onCreated callback sequencing in createAndAwaitMirror

Assert onCreated fires exactly once on CreateMirror success, before any clone polling/onStatus, and never on a CreateMirror error — pinning the placing-vs-cloning phase split.

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com
Entire-Checkpoint: bfb60c5675ab+110/-5