feat(store): NewestUnsummarizedVideoIDs for the onboarding cap

Returns up to limit of a user's newest videos (published_at DESC, NULLS LAST)
that have no summary yet. RLS-scoped via withUser — the test proves a second
user's newer video never leaks. Drives the connect-time onboarding burst
(Feature 1); the caller routes each through the shared rate gate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/adapters/store/videos.go

@@ -72,3 +72,41 @@ func nullTime(t time.Time) *time.Time {
 	}
 	return &t
 }
+
+// NewestUnsummarizedVideoIDs returns up to limit of the user's videos that have
+// no summary yet, newest first (published_at DESC, NULLS LAST). It caps the
+// connect-time onboarding burst (Feature 1) at a fixed count: the caller marks
+// these for summarization through the shared rate gate. RLS-scoped via withUser,
+// so it only ever sees the requesting user's rows. limit <= 0 returns nil.
+func (s *Store) NewestUnsummarizedVideoIDs(ctx context.Context, userID string, limit int) ([]string, error) {
+	if limit <= 0 {
+		return nil, nil
+	}
+	var ids []string
+	if err := s.withUser(ctx, userID, func(tx pgx.Tx) error {
+		rows, err := tx.Query(ctx,
+			`SELECT v.id
+			   FROM videos v
+			  WHERE v.user_id = $1
+			    AND NOT EXISTS (
+			          SELECT 1 FROM summaries su
+			           WHERE su.user_id = v.user_id AND su.video_id = v.id)
+			  ORDER BY v.published_at DESC NULLS LAST, v.seen_at DESC
+			  LIMIT $2`, userID, limit)
+		if err != nil {
+			return fmt.Errorf("store: newest unsummarized: %w", err)
+		}
+		defer rows.Close()
+		for rows.Next() {
+			var id string
+			if err := rows.Scan(&id); err != nil {
+				return fmt.Errorf("store: scan newest unsummarized: %w", err)
+			}
+			ids = append(ids, id)
+		}
+		return rows.Err()
+	}); err != nil {
+		return nil, err
+	}
+	return ids, nil
+}

internal/adapters/store/videos_test.go

@@ -81,3 +81,35 @@ func TestUpsertVideo_PerUserIsolation(t *testing.T) {
 
 	require.NotEqual(t, idA, idB, "same provider video for two users must be two distinct rows")
 }
+
+func TestNewestUnsummarizedVideoIDs(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	mk := func(user, pid string, day int) string {
+		v := ytVideo(user, pid, pid)
+		v.PublishedAt = time.Date(2026, 6, day, 12, 0, 0, 0, time.UTC)
+		id, err := s.UpsertVideo(ctx, v)
+		require.NoError(t, err)
+		return id
+	}
+
+	_ = mk(userA, "a1vid000001", 1)
+	id2 := mk(userA, "a2vid000002", 2)
+	id3 := mk(userA, "a3vid000003", 3)
+	id4 := mk(userA, "a4vid000004", 4)
+	mk(userB, "b1vid000009", 9) // userB's newest — must never leak via RLS
+
+	// The newest (v4) is summarized, so it's excluded from "unsummarized".
+	require.NoError(t, s.Deliver(ctx, summary(userA, id4, "done")))
+
+	// Cap 2, newest-first unsummarized: v3 then v2 (v4 excluded; userB excluded).
+	got, err := s.NewestUnsummarizedVideoIDs(ctx, userA, 2)
+	require.NoError(t, err)
+	require.Equal(t, []string{id3, id2}, got)
+
+	none, err := s.NewestUnsummarizedVideoIDs(ctx, userA, 0)
+	require.NoError(t, err)
+	require.Empty(t, none, "limit 0 returns nothing")
+}