feat(db): add similarity lookup queries (ListActiveContextualLikesForUser, GetCurrentSessionVectorForUser)

internal/db/queries/contextual_likes.sql

@@ -8,3 +8,14 @@ VALUES ($1, $2, $3, $4);
 UPDATE contextual_likes
 SET deleted_at = now()
 WHERE user_id = $1 AND track_id = $2 AND deleted_at IS NULL;
+
+-- name: ListActiveContextualLikesForUser :many
+-- Returns all the user's active (non-soft-deleted) contextual_likes with
+-- non-null vectors. Cardinality is bounded by the user's actual like-while-
+-- playing history — typically tens to low hundreds. Used by the engine to
+-- compute contextual_match_score for the candidate pool.
+SELECT track_id, session_vector
+FROM contextual_likes
+WHERE user_id = $1
+  AND deleted_at IS NULL
+  AND session_vector IS NOT NULL;

internal/db/queries/events.sql

@@ -66,3 +66,15 @@ LIMIT $3;
 UPDATE play_events
 SET session_vector_at_play = $2
 WHERE id = $1;
+
+-- name: GetCurrentSessionVectorForUser :one
+-- Returns the session_vector_at_play of the user's most recent play_event
+-- in a still-active (un-timed-out) session. NoRows means no current vector.
+-- Joined with play_sessions so closed sessions don't leak stale vectors.
+SELECT pe.session_vector_at_play
+FROM play_events pe
+JOIN play_sessions s ON s.id = pe.session_id
+WHERE pe.user_id = $1
+  AND s.ended_at IS NULL
+ORDER BY pe.started_at DESC
+LIMIT 1;