- Fix match pattern: `Ok(Ok(Err(_)))` must be treated as NOT a panic,
since execute_task_body returns Err(()) on task failure (not a panic).
Previously the Err path incorrectly set panicked=true, which could
cause pool to appear unhealthy.
- Add "task failed" log before retry/discard decision so real error
is visible in logs (previously only last_error on exhausted-retries
path was logged, which required hitting 5 retries to see the cause).
- Convert 3 remaining pool/mod.rs shorthand logs to format!() pattern.
8a0d2885f7