execute_step (6 tests): happy path, when=falsy → skipped, unknown action
→ ActionNotFound failure, retry budget exhaustion (attempts = 1 +
max_retries), retry recovery, and template-rendering of step params
against the run context.
with_retries (3 tests): first-try success returns attempts=1, recovery
returns the actual attempt that produced the result, and exhaustion
re-raises the last exception with the handler called 1 + max_retries
times.
All tests use backoff="none" to keep wall-clock time zero; timeout
testing is intentionally skipped (would need >= 1s per the int contract,
and exhaustion already locks that any Exception triggers retry).
