Replace FeedItem.priority with signals (#39)

* feat: replace FeedItem.priority with signals

Remove priority field from FeedItem and engine-level sorting.
Add FeedItemSignals with urgency and timeRelevance fields.
Update all source packages to emit signals instead of priority.

Ranking is now the post-processing layer's responsibility.
Urgency values are unchanged from the old priority values.

Co-authored-by: Ona <no-reply@ona.com>

* fix: use TimeRelevance enum in all tests

Co-authored-by: Ona <no-reply@ona.com>

---------

Co-authored-by: Ona <no-reply@ona.com>

packages/aris-core/src/feed.ts

@@ -1,3 +1,28 @@
+/**
+ * Source-provided hints for post-processors.
+ *
+ * Sources express domain-specific relevance without determining final ranking.
+ * Post-processors consume these signals alongside other inputs (user affinity,
+ * time of day, interaction history) to produce the final feed order.
+ */
+export const TimeRelevance = {
+	/** Needs attention now (e.g., event starting in minutes, severe alert) */
+	Imminent: "imminent",
+	/** Relevant soon (e.g., event in the next hour, approaching deadline) */
+	Upcoming: "upcoming",
+	/** Background information (e.g., daily forecast, low-priority status) */
+	Ambient: "ambient",
+} as const
+
+export type TimeRelevance = (typeof TimeRelevance)[keyof typeof TimeRelevance]
+
+export interface FeedItemSignals {
+	/** Source-assessed urgency (0-1). Post-processors use this as one ranking input. */
+	urgency?: number
+	/** How time-sensitive this item is relative to now. */
+	timeRelevance?: TimeRelevance
+}
+
 /**
  * A single item in the feed.
  *
@@ -8,9 +33,9 @@
  * const item: WeatherItem = {
  *   id: "weather-123",
  *   type: "weather",
- *   priority: 0.5,
  *   timestamp: new Date(),
  *   data: { temp: 18, condition: "cloudy" },
+ *   signals: { urgency: 0.5, timeRelevance: "ambient" },
  * }
  * ```
  */
@@ -22,10 +47,10 @@ export interface FeedItem<
 	id: string
 	/** Item type, matches the data source type */
 	type: TType
-	/** Sort priority (higher = more important, shown first) */
-	priority: number
 	/** When this item was generated */
 	timestamp: Date
 	/** Type-specific payload */
 	data: TData
+	/** Source-provided hints for post-processors. Optional — omit if no signals apply. */
+	signals?: FeedItemSignals
 }