Clarify phenology phase usage in advisory text

- Updated _output_format.md to specify guidelines for using `phenology_phase` in agronomic reasoning.
- Emphasized the importance of hedging language in Italian and avoiding present-tense certainty in advisory summaries.

prompts/_output_format.md

@@ -32,6 +32,17 @@ which is an earlier day; do not read dates in that block as the current day.
 meteorological window but one did occur within the past 25 days; its `date` is
 that spray day, not oggi.
 
+`phenology_phase` is the last reported observation in the input; it may lag the
+real field and is not a verified current stage. Still use it for agronomic
+reasoning (label BBCH windows, susceptibility), but never claim the crop *is*
+in that phase. Do not write present-tense certainty such as *ci troviamo in
+fase…*, *siamo in BBCH…*, or *la vite si trova in fase…*. Hedge in Italian,
+for example *poiché l'ultima fase fenologica di cui sono a conoscenza è …*,
+or in `full_advice` *la fase fenologica segnalata per oggi è …*. In
+`advice_summary`, do not use oggi / ieri / domani: use the "ultima fase di cui
+sono a conoscenza" form, or *la fase fenologica segnalata per il 13 aprile
+2026 è …*.
+
 ### Example shape
 
 {