- Add gap_significance_seconds constructor param (default 30) to replace hardcoded magic number in gap_count computation
- _parse_iso now returns datetime | None with try/except on ValueError; all callers handle None return by treating malformed timestamps as absent
- Extract reconstruct into four private helpers: _sort_entries, _group_into_raw_clusters, _build_cluster, _dominant_sources_tuple
- Promote _sort_key to module-level function (was nested inside reconstruct)
- Rename old module-level _build_cluster to _make_event_cluster to avoid name collision with new instance method
- Add explanatory comment to type: ignore[arg-type] at _highest_severity call site
- Black-formatted