Document template partials

docs/templates.md

@@ -13,6 +13,12 @@ Templates are Go `text/template` files. The current implemented templates are:
 - `internal/reporttemplate/templates/tomorrow.md.tmpl`
 - `internal/reporttemplate/templates/hourly.md.tmpl`
 
+Shared named partials live under `internal/reporttemplate/templates/partials/`:
+
+- `daypart_forecast.md.tmpl`, used by Daily and Tomorrow
+- `today_daypart_forecast.md.tmpl`, used by Today
+- `precipitation_timing.md.tmpl`, used by Daily, Today, and Tomorrow
+
 Templates are rendered from structured contexts such as `DailyRenderContext`,
 `TodayRenderContext`, `TomorrowRenderContext`, and `HourlyRenderContext`.
 Weather data collection, derivation, module execution, generated text
@@ -27,6 +33,9 @@ validation, and artifact paths are handled before template rendering.
   templates.
 - Missing template keys are errors. A misspelled variable will fail rendering.
 - No custom template functions are currently registered.
+- Named partials are invoked with `{{ template "name" . }}`. Pass the current
+  render context (`.`) unless the partial is intentionally designed for a
+  narrower value.
 - Optional module stanzas are pointers and should be guarded with
   `{{ with .Modules.WeatherStory }}...{{ end }}`.
 - Slices can be rendered with `{{ range .Items }}...{{ else }}...{{ end }}`.
@@ -131,6 +140,8 @@ Daily generated text uses `.GeneratedText.Summary`,
 `.GeneratedText.Confidence`. Forecast discussion is a slice of paragraphs and
 should be rendered with `range`.
 
+Daily uses the shared `daypart_forecast` and `precipitation_timing` partials.
+
 Daily uses template ID `daily`, generated-text schema ID `daily`, and prompt
 source `internal/reporttemplate/prompts/daily.generated_text.md`.
 
@@ -162,6 +173,10 @@ Today generated text uses `.GeneratedText.Summary`,
 `.GeneratedText.Confidence`. Forecast discussion is a slice of paragraphs and
 should be rendered with `range`.
 
+Today uses the `today_daypart_forecast` partial so elapsed or missing dayparts
+can be omitted while Daily and Tomorrow keep their fallback row. It also uses
+the shared `precipitation_timing` partial.
+
 Today uses template ID `today`, generated-text schema ID `today`, and prompt
 source `internal/reporttemplate/prompts/today.generated_text.md`.
 
@@ -282,6 +297,10 @@ Daily, Today, and Tomorrow templates should use `.Modules.Dayparts` for
 ordered daypart rendering. Each item has `Key` and `Summary`; `Summary` is a
 rich `briefing.DerivedDaypartSummaryModule`.
 
+The shared daypart partials render from these same `.Modules.Dayparts` values.
+Edit `daypart_forecast.md.tmpl` for common Daily/Tomorrow wording, and edit
+`today_daypart_forecast.md.tmpl` for Today-specific omission behavior.
+
 Common rich daypart fields:
 
 | Variable | Type | Description |