fix(subscription): surface favorite timestamp under favoriteUpdatedAt (#423)

Author: chenjr0719

docs/client-api.md

@@ -665,7 +665,7 @@ user-service endpoints via room-service's `GetRoomsInfo` enrichment. `room` is
 | `restricted` | boolean | Optional. Denormalized room restricted flag. |
 | `externalAccess` | boolean | Optional. Denormalized room external-access flag. |
 | `room` | [SubscriptionRoom](#subscriptionroom) | Optional. Room-derived view (read-time enrichment; user-service endpoints only). |
-| `favoritedAt` | RFC3339 timestamp | Optional. When the user favorited the room. |
+| `favoriteUpdatedAt` | RFC3339 timestamp | Optional. Last time the user toggled favorite on the room (also bumped on un-favorite). |
 | `updatedAt` | RFC3339 timestamp | Optional. When the subscription was last updated. |
 
 #### SubscriptionRoom

pkg/model/model_test.go

@@ -4079,19 +4079,19 @@ func TestSubscriptionEnrichmentFields_RoundTrip(t *testing.T) {
 }
 
 func TestSubscriptionBaseMetadata_RoundTrip(t *testing.T) {
-	favoritedAt := time.Date(2026, 2, 1, 9, 0, 0, 0, time.UTC)
+	favoriteUpdatedAt := time.Date(2026, 2, 1, 9, 0, 0, 0, time.UTC)
 	updatedAt := time.Date(2026, 3, 2, 10, 0, 0, 0, time.UTC)
 	src := model.Subscription{
-		ID:          "s1",
-		User:        model.SubscriptionUser{ID: "u1", Account: "alice"},
-		RoomID:      "r1",
-		SiteID:      "site-a",
-		Roles:       []model.Role{model.RoleMember},
-		RoomType:    model.RoomTypeChannel,
-		JoinedAt:    time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC),
-		HasUnread:   true,
-		FavoritedAt: &favoritedAt,
-		UpdatedAt:   &updatedAt,
+		ID:                "s1",
+		User:              model.SubscriptionUser{ID: "u1", Account: "alice"},
+		RoomID:            "r1",
+		SiteID:            "site-a",
+		Roles:             []model.Role{model.RoleMember},
+		RoomType:          model.RoomTypeChannel,
+		JoinedAt:          time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC),
+		HasUnread:         true,
+		FavoriteUpdatedAt: &favoriteUpdatedAt,
+		UpdatedAt:         &updatedAt,
 	}
 	dst := model.Subscription{}
 	roundTrip(t, &src, &dst)
@@ -4107,7 +4107,7 @@ func TestSubscriptionBaseMetadata_RoundTrip(t *testing.T) {
 	zb, err := json.Marshal(&model.Subscription{ID: "z", JoinedAt: time.Now().UTC()})
 	require.NoError(t, err)
 	require.NoError(t, json.Unmarshal(zb, &zero))
-	for _, k := range []string{"favoritedAt", "updatedAt"} {
+	for _, k := range []string{"favoriteUpdatedAt", "updatedAt"} {
 		_, present := zero[k]
 		assert.False(t, present, "%q must be omitted when unset", k)
 	}

pkg/model/subscription.go

@@ -58,7 +58,9 @@ type Subscription struct {
 	// Subscription-level metadata persisted on the Mongo subscriptions document.
 	// UpdatedAt is a nullable pointer so a creating writer that doesn't stamp it
 	// (e.g. room-worker's $setOnInsert) never persists a zero-time placeholder.
-	FavoritedAt *time.Time `json:"favoritedAt,omitempty" bson:"favoritedAt,omitempty"`
+	// Last favorite-toggle time (also bumped on un-favorite). bson key matches what the
+	// writers store; the old `favoritedAt` key was never written, so the value never surfaced.
+	FavoriteUpdatedAt *time.Time `json:"favoriteUpdatedAt,omitempty" bson:"favoriteUpdatedAt,omitempty"`
 	// Stored as `_updatedAt` in Mongo (matches the canonical subscriptions schema);
 	// serialized on the wire as `updatedAt`. Rooms keep the plain `updatedAt` field.
 	UpdatedAt *time.Time `json:"updatedAt,omitempty" bson:"_updatedAt,omitempty"`

user-service/mongorepo/subscriptions.go

@@ -177,14 +177,14 @@ func subscriptionProjection(extra bson.M) bson.M {
 		"hasMention":         1,
 		// hasGroupMention removed from the schema; hasUnread is computed at read
 		// time (bson:"-"). Neither is projected from Mongo.
-		"threadUnread":   1,
-		"alert":          1,
-		"muted":          1,
-		"favorite":       1,
-		"restricted":     1,
-		"externalAccess": 1,
-		"favoritedAt":    1,
-		"_updatedAt":     1, // subscription's Mongo field (wire: updatedAt)
+		"threadUnread":      1,
+		"alert":             1,
+		"muted":             1,
+		"favorite":          1,
+		"restricted":        1,
+		"externalAccess":    1,
+		"favoriteUpdatedAt": 1,
+		"_updatedAt":        1, // subscription's Mongo field (wire: updatedAt)
 		// room baseline copied to the top level (consumed by local enrichment)
 		"userCount":         1,
 		"lastMsgAt":         1,