Addresses P1 feedback from QA verdict on 11108b3:
- Retry-path tests: 429-then-200, 500-then-200, persistent-502 exhausts
all attempts and throws.
- Validator guardrail test: validate_credentials_detailed() asserts
wp_remote_post is never called, locking in the non-destructive probe
contract so no "Test Connection" click ever burns image-gen budget.
- Validator edge case: missing account_id returns 'account_id_empty'
without touching the network.
- Bootstrap retry delay set to 0 in tests so the new retry-loop tests
don't spend real wall time in sleep(). Production value unchanged
(PRAUTOBLOGGER_RETRY_BASE_DELAY_SECONDS = 2 in prautoblogger.php).
Risk flags:
- No code under test changed. Same provider diff as 11108b3; this
commit is purely additional coverage + a zero-impact bootstrap tweak.
Agent-Session: cowork-2026-04-15-image-pipeline-commit-1a-qa-fixup
c8236189cd