fix(taste): drop unused now param + tighten test (golangci-lint revive)

golangci-lint v2 (CI-only; local is v1) flagged two unused-parameter issues:
- BuildTasteProfile's `now` was genuinely dead — decay/windowing are computed
  DB-side via now(), so no Go-side timestamp is threaded. Removed it (a
  phase-3 context model that needs a pinned reference time would re-add it);
  updated the scheduler call site.
- the degenerate-params engagement test ignored t; reworked it to assert the
  result stays in [-1,1], which also strengthens the test.

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

internal/playlists/scheduler.go

@@ -227,7 +227,7 @@ func (s *Scheduler) runStartupCatchUp(ctx context.Context, users []dbq.ListActiv
 // build can read a fresh profile (phase-2 consumption); both steps are
 // best-effort and a failure in one is logged without blocking the other.
 func (s *Scheduler) rebuildUserDaily(ctx context.Context, userID pgtype.UUID, now time.Time) {
-	if err := taste.BuildTasteProfile(ctx, s.pool, s.logger, userID, now, taste.DefaultConfig()); err != nil {
+	if err := taste.BuildTasteProfile(ctx, s.pool, s.logger, userID, taste.DefaultConfig()); err != nil {
 		s.logger.Warn("scheduler: taste profile rebuild failed",
 			"user_id", uuidStringPL(userID), "err", err)
 	}

internal/taste/engagement_test.go

@@ -44,11 +44,15 @@ func TestEngagement_MonotonicNonDecreasing(t *testing.T) {
 	}
 }
 
-func TestEngagement_DegenerateParamsNoPanic(t *testing.T) {
-	// Non-increasing thresholds must collapse ramps, not divide by zero.
+func TestEngagement_DegenerateParamsStayInRange(t *testing.T) {
+	// Non-increasing thresholds must collapse ramps (no divide-by-zero) and
+	// still produce a value in [-1, 1].
 	p := EngagementParams{HardSkip: 0.5, NeutralCompletion: 0.5, FullCompletion: 0.5}
 	for _, c := range []float64{0, 0.25, 0.5, 0.75, 1} {
-		_ = Engagement(c, p)
+		got := Engagement(c, p)
+		if got < -1 || got > 1 {
+			t.Errorf("Engagement(%.2f) = %.3f out of [-1,1]", c, got)
+		}
 	}
 }
 

internal/taste/profile.go

@@ -11,7 +11,6 @@ import (
 	"log/slog"
 	"sort"
 	"strings"
-	"time"
 
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/jackc/pgx/v5/pgxpool"
@@ -81,9 +80,13 @@ func DefaultConfig() Config {
 // Self-contained transaction for the replace. Returns an error only on a
 // fatal DB failure; the daily caller logs and proceeds to playlist building
 // regardless (best-effort).
+//
+// The decay reference time is the database clock (age is computed in SQL via
+// now()), so no Go-side timestamp is threaded here; a phase-3 context model
+// that needs a pinned reference time would add one.
 func BuildTasteProfile(
 	ctx context.Context, pool *pgxpool.Pool, logger *slog.Logger,
-	userID pgtype.UUID, now time.Time, cfg Config,
+	userID pgtype.UUID, cfg Config,
 ) error {
 	q := dbq.New(pool)
 

internal/taste/profile_db_test.go

@@ -155,7 +155,7 @@ func TestBuildTasteProfile_PositiveVsNegative(t *testing.T) {
 		seedPlay(t, pool, u.ID, skippedTrack.ID, now.Add(-time.Duration(i+1)*time.Hour), 0.02)
 	}
 
-	if err := BuildTasteProfile(context.Background(), pool, discardLogger(), u.ID, now, DefaultConfig()); err != nil {
+	if err := BuildTasteProfile(context.Background(), pool, discardLogger(), u.ID, DefaultConfig()); err != nil {
 		t.Fatalf("build: %v", err)
 	}
 
@@ -190,7 +190,7 @@ func TestBuildTasteProfile_AggregationProtectsArtist(t *testing.T) {
 	skipTrack := seedTrack(t, pool, fav.ID, "Indie")
 	seedPlay(t, pool, u.ID, skipTrack.ID, now.Add(-2*time.Hour), 0.02)
 
-	if err := BuildTasteProfile(context.Background(), pool, discardLogger(), u.ID, now, DefaultConfig()); err != nil {
+	if err := BuildTasteProfile(context.Background(), pool, discardLogger(), u.ID, DefaultConfig()); err != nil {
 		t.Fatalf("build: %v", err)
 	}
 	w, ok := artistWeight(t, pool, u.ID, fav.ID)
@@ -203,7 +203,6 @@ func TestBuildTasteProfile_AggregationProtectsArtist(t *testing.T) {
 // plays still earns a positive weight from the like bonus.
 func TestBuildTasteProfile_ArtistLikeBonus(t *testing.T) {
 	pool := newPool(t)
-	now := time.Now().UTC()
 	u := seedUser(t, pool, "tp3")
 	liked := seedArtist(t, pool, "LikedOnly")
 	if _, err := pool.Exec(context.Background(),
@@ -212,7 +211,7 @@ func TestBuildTasteProfile_ArtistLikeBonus(t *testing.T) {
 		t.Fatalf("seed artist like: %v", err)
 	}
 
-	if err := BuildTasteProfile(context.Background(), pool, discardLogger(), u.ID, now, DefaultConfig()); err != nil {
+	if err := BuildTasteProfile(context.Background(), pool, discardLogger(), u.ID, DefaultConfig()); err != nil {
 		t.Fatalf("build: %v", err)
 	}
 	w, ok := artistWeight(t, pool, u.ID, liked.ID)
@@ -240,7 +239,7 @@ func TestBuildTasteProfile_AtomicReplace(t *testing.T) {
 		return n
 	}
 	for i := 0; i < 2; i++ {
-		if err := BuildTasteProfile(ctx, pool, discardLogger(), u.ID, now, DefaultConfig()); err != nil {
+		if err := BuildTasteProfile(ctx, pool, discardLogger(), u.ID, DefaultConfig()); err != nil {
 			t.Fatalf("build %d: %v", i, err)
 		}
 	}