Require precipitation timing in generated text

internal/promptassets/assets/prompts/hourly/hourly_generated_text.user.md

@@ -8,8 +8,7 @@ Return these fields:
 
 - `summary`: required. One or two sentences summarizing the main weather story for the valid period.
 - `forecast_discussion`: required. Two or three sentences explaining the broader setup, trend, or forecast reasoning most relevant to the valid period.
-- `precipitation_timing`: optional. Include only when the deterministic `precip_timing` module contains precipitation windows.
-- `confidence`: optional. Include only if uncertainty, timing spread, or conflicting signals materially affect how the reader should interpret the forecast.
+- `precipitation_timing`: required. When the deterministic `precip_timing` module contains precipitation windows, provide the supported timing prose described below. Otherwise, return an empty string (`""`).
 
 Return JSON only.
 
@@ -25,4 +24,4 @@ Use narrative products to explain the “why” behind the local forecast when u
 
 # Precipitation timing
 
-Include this only if precipitation is forecast. Use one to four sentences to give practical context about a supported frontal, convective, or stratiform setup; expected type, intensity, and duration; and uncertainty in onset or duration.
+When precipitation windows are present, use one to four sentences to give practical context about a supported frontal, convective, or stratiform setup; expected type, intensity, and duration; and uncertainty in onset or duration. When no precipitation windows are present, return an empty string (`""`) for `precipitation_timing`.