feat(tuning): scoring weights → DB-backed admin tuning lab

The recommendation scoring knobs move out of YAML (radio profile) and
out of the systemMixWeights hard-code (daily_mix profile) into
DB-backed settings with live effect (#1250) — the defaults-discovery
lab per decision #1247: the operator turns knobs to find good values,
which then get baked back into shipped defaults; end users and other
operators should never need the card.

- Migration 0040: recommendation_weight_profiles (radio / daily_mix,
  8 weight columns), taste_tuning singleton (engagement half-life +
  completion-curve points), recommendation_tuning_audit (one row per
  change with a {field, old, new} diff — the trend view's markers,
  #1251).
- internal/recsettings: boot reconcile seeds shipped defaults without
  clobbering tuned rows (coverart SettingsService pattern), validates
  patches (bounds, curve ordering), writes audit rows, and pushes
  daily_mix weights + taste config into package playlists. No-op
  patches write no audit row.
- playlists gains SetSystemMixWeights / SetTasteConfig swap points
  under a RWMutex — no signature threading through the producers; the
  scheduler's taste rebuild reads the pushed config.
- Radio reads its weight profile from the service per request; the 8
  weight fields leave config.RecommendationConfig (YAML keeps only
  RecentlyPlayedHours / RadioSize / RadioSizeMax).
- Admin API: GET/PATCH/reset under /api/admin/recommendation-tuning,
  echoing current + shipped values.
- Web: new admin Tuning tab — two weight profiles side by side, taste
  card, per-scope save (changed fields only) + reset, deviation dots
  against shipped defaults.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TsF3cNoKrqCYsU78cXC8U6

internal/recsettings/service_test.go

@@ -0,0 +1,222 @@
+package recsettings
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io"
+	"log/slog"
+	"os"
+	"testing"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/dbtest"
+)
+
+func newPool(t *testing.T) *pgxpool.Pool {
+	t.Helper()
+	if testing.Short() {
+		t.Skip("skipping integration test in -short mode")
+	}
+	dsn := os.Getenv("MINSTREL_TEST_DATABASE_URL")
+	if dsn == "" {
+		t.Skip("MINSTREL_TEST_DATABASE_URL not set")
+	}
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+	if err := db.Migrate(dsn, logger); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+	pool, err := pgxpool.New(context.Background(), dsn)
+	if err != nil {
+		t.Fatalf("pool: %v", err)
+	}
+	t.Cleanup(pool.Close)
+	dbtest.ResetDB(t, pool)
+	return pool
+}
+
+func newService(t *testing.T, pool *pgxpool.Pool) *Service {
+	t.Helper()
+	s, err := New(context.Background(), pool, slog.New(slog.NewTextHandler(io.Discard, nil)))
+	if err != nil {
+		t.Fatalf("recsettings.New: %v", err)
+	}
+	return s
+}
+
+func auditRows(t *testing.T, pool *pgxpool.Pool) []struct {
+	Scope, Action string
+	Changes       []fieldChange
+} {
+	t.Helper()
+	rows, err := pool.Query(context.Background(),
+		`SELECT scope, action, changes FROM recommendation_tuning_audit ORDER BY id`)
+	if err != nil {
+		t.Fatalf("query audit: %v", err)
+	}
+	defer rows.Close()
+	var out []struct {
+		Scope, Action string
+		Changes       []fieldChange
+	}
+	for rows.Next() {
+		var scope, action string
+		var raw []byte
+		if err := rows.Scan(&scope, &action, &raw); err != nil {
+			t.Fatalf("scan audit: %v", err)
+		}
+		var changes []fieldChange
+		if err := json.Unmarshal(raw, &changes); err != nil {
+			t.Fatalf("unmarshal audit changes: %v", err)
+		}
+		out = append(out, struct {
+			Scope, Action string
+			Changes       []fieldChange
+		}{scope, action, changes})
+	}
+	return out
+}
+
+func TestNew_SeedsShippedDefaults(t *testing.T) {
+	pool := newPool(t)
+	s := newService(t, pool)
+	if got := s.Weights(ScopeRadio); got != ShippedRadioWeights() {
+		t.Errorf("radio weights = %+v, want shipped defaults", got)
+	}
+	if got := s.Weights(ScopeDailyMix); got != ShippedDailyMixWeights() {
+		t.Errorf("daily_mix weights = %+v, want shipped defaults", got)
+	}
+	if got := s.Taste(); got != ShippedTasteTuning() {
+		t.Errorf("taste tuning = %+v, want shipped defaults", got)
+	}
+	// Seeding must not write audit rows — nothing changed.
+	if rows := auditRows(t, pool); len(rows) != 0 {
+		t.Errorf("boot reconcile wrote %d audit rows, want 0", len(rows))
+	}
+}
+
+func TestUpdateProfile_PersistsAndAudits(t *testing.T) {
+	pool := newPool(t)
+	s := newService(t, pool)
+	if err := s.UpdateProfile(context.Background(), ScopeRadio,
+		map[string]float64{"taste_weight": 2.5, "skip_penalty": 3.0}); err != nil {
+		t.Fatalf("UpdateProfile: %v", err)
+	}
+	got := s.Weights(ScopeRadio)
+	if got.TasteWeight != 2.5 || got.SkipPenalty != 3.0 {
+		t.Errorf("weights = %+v, want taste 2.5 / skip 3.0", got)
+	}
+	// The other profile is untouched.
+	if s.Weights(ScopeDailyMix) != ShippedDailyMixWeights() {
+		t.Error("daily_mix must be unaffected by a radio update")
+	}
+	// Values survive a fresh boot (persisted, not just cached), and the
+	// reconcile's ON CONFLICT DO NOTHING doesn't clobber tuned rows.
+	s2 := newService(t, pool)
+	if got := s2.Weights(ScopeRadio); got.TasteWeight != 2.5 {
+		t.Errorf("rebooted taste_weight = %v, want 2.5", got.TasteWeight)
+	}
+	rows := auditRows(t, pool)
+	if len(rows) != 1 {
+		t.Fatalf("audit rows = %d, want 1", len(rows))
+	}
+	if rows[0].Scope != ScopeRadio || rows[0].Action != "update" || len(rows[0].Changes) != 2 {
+		t.Errorf("audit row = %+v, want radio/update with 2 changes", rows[0])
+	}
+	// Changes are field-sorted: skip_penalty before taste_weight.
+	if rows[0].Changes[0].Field != "skip_penalty" || rows[0].Changes[0].New != 3.0 {
+		t.Errorf("changes[0] = %+v, want skip_penalty → 3.0", rows[0].Changes[0])
+	}
+}
+
+func TestUpdateProfile_Validation(t *testing.T) {
+	pool := newPool(t)
+	s := newService(t, pool)
+	cases := []struct {
+		name  string
+		scope string
+		patch map[string]float64
+		want  error
+	}{
+		{"unknown scope", "banana", map[string]float64{"taste_weight": 1}, ErrUnknownScope},
+		{"unknown field", ScopeRadio, map[string]float64{"vibes": 1}, ErrUnknownField},
+		{"over bound", ScopeRadio, map[string]float64{"taste_weight": 11}, ErrOutOfRange},
+		{"negative jitter", ScopeRadio, map[string]float64{"jitter_magnitude": -0.1}, ErrOutOfRange},
+	}
+	for _, c := range cases {
+		if err := s.UpdateProfile(context.Background(), c.scope, c.patch); !errors.Is(err, c.want) {
+			t.Errorf("%s: err = %v, want %v", c.name, err, c.want)
+		}
+	}
+	if s.Weights(ScopeRadio) != ShippedRadioWeights() {
+		t.Error("rejected patches must not partially apply")
+	}
+	if rows := auditRows(t, pool); len(rows) != 0 {
+		t.Errorf("rejected patches wrote %d audit rows, want 0", len(rows))
+	}
+}
+
+func TestUpdateTaste_CurveOrderingEnforced(t *testing.T) {
+	pool := newPool(t)
+	s := newService(t, pool)
+	// Moving neutral above full must reject on the PATCHED result.
+	err := s.UpdateTaste(context.Background(), map[string]float64{"engagement_neutral": 0.95})
+	if !errors.Is(err, ErrOutOfRange) {
+		t.Fatalf("err = %v, want ErrOutOfRange (curve ordering)", err)
+	}
+	// A coherent multi-point move is fine.
+	if err := s.UpdateTaste(context.Background(), map[string]float64{
+		"engagement_neutral": 0.40, "engagement_full": 0.95, "half_life_days": 30,
+	}); err != nil {
+		t.Fatalf("UpdateTaste: %v", err)
+	}
+	cfg := s.TasteConfig()
+	if cfg.HalfLifeDays != 30 || cfg.Engagement.NeutralCompletion != 0.40 {
+		t.Errorf("taste config = %+v, want tuned values", cfg)
+	}
+	// WindowDays scales with the half-life at the shipped ratio.
+	if cfg.WindowDays != 30*3.6 {
+		t.Errorf("WindowDays = %v, want %v", cfg.WindowDays, 30*3.6)
+	}
+}
+
+func TestReset_RestoresShippedAndAudits(t *testing.T) {
+	pool := newPool(t)
+	s := newService(t, pool)
+	// Reset with nothing changed is a no-op (no audit row).
+	if err := s.Reset(context.Background(), ScopeDailyMix); err != nil {
+		t.Fatalf("no-op reset: %v", err)
+	}
+	if rows := auditRows(t, pool); len(rows) != 0 {
+		t.Fatalf("no-op reset wrote audit rows")
+	}
+	if err := s.UpdateProfile(context.Background(), ScopeDailyMix,
+		map[string]float64{"similarity_weight": 4}); err != nil {
+		t.Fatalf("UpdateProfile: %v", err)
+	}
+	if err := s.Reset(context.Background(), ScopeDailyMix); err != nil {
+		t.Fatalf("Reset: %v", err)
+	}
+	if s.Weights(ScopeDailyMix) != ShippedDailyMixWeights() {
+		t.Error("reset must restore shipped defaults")
+	}
+	rows := auditRows(t, pool)
+	if len(rows) != 2 || rows[1].Action != "reset" {
+		t.Fatalf("audit rows = %+v, want update then reset", rows)
+	}
+}
+
+func TestUpdate_NoOpWritesNoAudit(t *testing.T) {
+	pool := newPool(t)
+	s := newService(t, pool)
+	shipped := ShippedRadioWeights()
+	if err := s.UpdateProfile(context.Background(), ScopeRadio,
+		map[string]float64{"taste_weight": shipped.TasteWeight}); err != nil {
+		t.Fatalf("UpdateProfile: %v", err)
+	}
+	if rows := auditRows(t, pool); len(rows) != 0 {
+		t.Errorf("no-op update wrote %d audit rows, want 0", len(rows))
+	}
+}