Document near-term report behavior

docs/internal/facts.md

@@ -27,6 +27,12 @@ Outputs:
   report-period SPC convective outlooks and discussions, daily summaries,
   daypart summaries, and Storm Report window summary
 
+Near-Term Report uses the generic valid-period hourly and narrative selection
+for its rolling six-hour window. Its derived facts include precipitation timing
+from the selected hourly periods, alert overlaps for the six-hour period, and
+SPC outlooks/discussions overlapping that period. It does not build daily
+summaries, daypart summaries, or a storm-window summary.
+
 ## Boundaries
 
 - This package owns fact assembly and reusable deterministic derivation for a
@@ -62,6 +68,8 @@ and inspection.
 - Invalid timezone names return an error.
 - Missing required hourly forecast data returns the underlying forecast
   derivation error for reports that require daily summaries.
+- Near-Term Report can derive its default module facts without daily or
+  daypart summaries.
 - Missing optional narrative, alert, discussion, daily, or weather story data
   produces empty or nil derived fields.
 - Missing optional SPC convective outlook data produces a nil collected field.