feat(db): add contextual_likes table (M3 session-context capture)

Table was referenced in migration 0005's comment but never created —
this slice fills the gap. Soft-delete via deleted_at column; hot-path
partial index on active rows; GIN index on session_vector for
M3 sub-plan #3's similarity queries.

internal/db/dbq/contextual_likes.sql.go

@@ -0,0 +1,52 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.31.1
+// source: contextual_likes.sql
+
+package dbq
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+const insertContextualLike = `-- name: InsertContextualLike :exec
+INSERT INTO contextual_likes (user_id, track_id, session_vector, session_id)
+VALUES ($1, $2, $3, $4)
+`
+
+type InsertContextualLikeParams struct {
+	UserID        pgtype.UUID
+	TrackID       pgtype.UUID
+	SessionVector []byte
+	SessionID     pgtype.UUID
+}
+
+func (q *Queries) InsertContextualLike(ctx context.Context, arg InsertContextualLikeParams) error {
+	_, err := q.db.Exec(ctx, insertContextualLike,
+		arg.UserID,
+		arg.TrackID,
+		arg.SessionVector,
+		arg.SessionID,
+	)
+	return err
+}
+
+const softDeleteContextualLikesForUserTrack = `-- name: SoftDeleteContextualLikesForUserTrack :exec
+UPDATE contextual_likes
+SET deleted_at = now()
+WHERE user_id = $1 AND track_id = $2 AND deleted_at IS NULL
+`
+
+type SoftDeleteContextualLikesForUserTrackParams struct {
+	UserID  pgtype.UUID
+	TrackID pgtype.UUID
+}
+
+// Marks all currently-active rows for (user, track) as deleted. Idempotent —
+// already-deleted rows aren't re-touched.
+func (q *Queries) SoftDeleteContextualLikesForUserTrack(ctx context.Context, arg SoftDeleteContextualLikesForUserTrackParams) error {
+	_, err := q.db.Exec(ctx, softDeleteContextualLikesForUserTrack, arg.UserID, arg.TrackID)
+	return err
+}

internal/db/dbq/models.go

@@ -29,6 +29,16 @@ type Artist struct {
 	UpdatedAt pgtype.Timestamptz
 }
 
+type ContextualLike struct {
+	ID            pgtype.UUID
+	UserID        pgtype.UUID
+	TrackID       pgtype.UUID
+	LikedAt       pgtype.Timestamptz
+	DeletedAt     pgtype.Timestamptz
+	SessionVector []byte
+	SessionID     pgtype.UUID
+}
+
 type GeneralLike struct {
 	UserID  pgtype.UUID
 	TrackID pgtype.UUID

internal/db/migrations/0007_contextual_likes.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS contextual_likes;

internal/db/migrations/0007_contextual_likes.up.sql

@@ -0,0 +1,32 @@
+-- contextual_likes captures a per-session-context snapshot at the time of
+-- each like. The recommendation engine in M3 sub-plan #3 uses these rows
+-- to compute contextual_match_score per (current session, candidate track).
+--
+-- Multiple rows per (user, track) are allowed and expected — each row
+-- represents a like in a specific session context. Soft-deleted rows
+-- remain in the table (deleted_at populated) but are filtered out of the
+-- engine's queries via the partial index. Re-liking a previously-unliked
+-- track adds a NEW row (does not undelete the old one).
+--
+-- Note: the M2 events migration (0005) commented that contextual_likes
+-- "ships nullable now" but the actual CREATE TABLE was missed. This slice
+-- ships the table for the first time.
+
+CREATE TABLE contextual_likes (
+    id              uuid        PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id         uuid        NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    track_id        uuid        NOT NULL REFERENCES tracks(id) ON DELETE CASCADE,
+    liked_at        timestamptz NOT NULL DEFAULT now(),
+    deleted_at      timestamptz,
+    session_vector  jsonb,
+    session_id      uuid REFERENCES play_sessions(id) ON DELETE SET NULL
+);
+
+-- Hot path for both the engine's lookups and the soft-delete UPDATE.
+CREATE INDEX contextual_likes_active_idx
+    ON contextual_likes (user_id, track_id)
+    WHERE deleted_at IS NULL;
+
+-- Vector similarity queries from M3 sub-plan #3 will use this.
+CREATE INDEX contextual_likes_vector_idx
+    ON contextual_likes USING gin (session_vector);

internal/db/queries/contextual_likes.sql

@@ -0,0 +1,10 @@
+-- name: InsertContextualLike :exec
+INSERT INTO contextual_likes (user_id, track_id, session_vector, session_id)
+VALUES ($1, $2, $3, $4);
+
+-- name: SoftDeleteContextualLikesForUserTrack :exec
+-- Marks all currently-active rows for (user, track) as deleted. Idempotent —
+-- already-deleted rows aren't re-touched.
+UPDATE contextual_likes
+SET deleted_at = now()
+WHERE user_id = $1 AND track_id = $2 AND deleted_at IS NULL;