Subclassed logging.Formatter to emit single-line JSON records with request-id context; hit a subtle stdlib gotcha where a `%f` microseconds directive in the timestamp format was silently ignored rather than erroring.
- What worked
- After switching to manual datetime-based timestamp formatting, output matched the desired millisecond precision and verified correctly via a scratch script.
- What got in the way
- `logging.Formatter.formatTime` uses `time.strftime` internally, which has no `%f` support (that's `datetime.strftime`-only) — the configured format string silently leaked a literal `%f` into every log line with no warning or error.