fix: address code review findings

- Start Web UI before the blocking initial sync so the dashboard is
  reachable during the (rate-limited, potentially multi-minute) first
  sync; fold the immediate sync into startPeriodicSync's overlap guard
  so it can never race a concurrent tick over the shared DB / MB client.
- Make MarkNotificationSent idempotent: INSERT OR IGNORE for same-second
  PK collisions, and explicitly swallow FK violations when a release was
  pruned by a concurrent re-sync. Prevents a single vanished/duplicate
  release from aborting the digest mark-sent loop and re-sending.
- Do not abort NotifyOnce's mark-sent loop on a single failure; log and
  continue so every release in the batch is marked.
- NULL-safe reads: COALESCE(type,''), COALESCE(release_date,'') in the
  external_releases and unnotified readers to match the cache reader.
- Update/extend tests for the new idempotency and startup contracts.

internal/database/external_releases.go

@@ -52,7 +52,7 @@ func GetExternalRelease(db *DB, rgid string) (*ExternalRelease, error) {
 	var cachedAt sql.NullTime
 	var secondaryTypes sql.NullString
 	err := db.Conn().QueryRow(
-		"SELECT rgid, artist_id, title, type, release_date, is_ignored, cached_at, secondary_types FROM external_releases WHERE rgid = ?",
+		"SELECT rgid, artist_id, title, COALESCE(type,''), COALESCE(release_date,''), is_ignored, cached_at, secondary_types FROM external_releases WHERE rgid = ?",
 		rgid,
 	).Scan(&r.RGID, &r.ArtistID, &r.Title, &r.Type, &r.ReleaseDate, &r.IsIgnored, &cachedAt, &secondaryTypes)
 	if err != nil {
@@ -83,7 +83,7 @@ func SaveExternalRelease(db *DB, release *ExternalRelease) error {
 // GetExternalReleasesByArtist returns all external_release rows for a given artist_id.
 func GetExternalReleasesByArtist(db *DB, artistID string) ([]ExternalRelease, error) {
 	rows, err := db.Conn().Query(
-		"SELECT rgid, artist_id, title, type, release_date, is_ignored, cached_at, secondary_types FROM external_releases WHERE artist_id = ?",
+		"SELECT rgid, artist_id, title, COALESCE(type,''), COALESCE(release_date,''), is_ignored, cached_at, secondary_types FROM external_releases WHERE artist_id = ?",
 		artistID,
 	)
 	if err != nil {
@@ -116,7 +116,7 @@ func GetExternalReleasesByArtist(db *DB, artistID string) ([]ExternalRelease, er
 // GetIgnoredReleases returns all external_release rows where is_ignored = 1.
 func GetIgnoredReleases(db *DB) ([]ExternalRelease, error) {
 	rows, err := db.Conn().Query(
-		"SELECT rgid, artist_id, title, type, release_date, is_ignored, cached_at, secondary_types FROM external_releases WHERE is_ignored = 1",
+		"SELECT rgid, artist_id, title, COALESCE(type,''), COALESCE(release_date,''), is_ignored, cached_at, secondary_types FROM external_releases WHERE is_ignored = 1",
 	)
 	if err != nil {
 		return nil, fmt.Errorf("query ignored releases: %w", err)

internal/database/notifications.go

@@ -1,16 +1,37 @@
 package database
 
 import (
+	"errors"
 	"fmt"
+
+	sqlite3 "github.com/mattn/go-sqlite3"
 )
 
 // MarkNotificationSent records that a notification has been sent for the given RGID.
+//
+// Uses INSERT OR IGNORE so a pre-existing marker for the same RGID (a
+// same-second re-notify colliding on the (rgid, sent_at) primary key) is a
+// no-op rather than an error: the marker's presence, not its exact timestamp,
+// is what matters for idempotency.
+//
+// A concurrent re-sync that prunes the external_releases row before this insert
+// would violate the FK constraint. OR IGNORE does NOT downgrade FK violations
+// in this SQLite build, so the FK error is caught explicitly and treated as a
+// benign no-op ("the release is already gone"). This ensures a single vanished
+// release cannot abort a whole digest's mark-sent loop and trigger duplicate
+// notifications on the next run.
 func MarkNotificationSent(db *DB, rgid string) error {
 	_, err := db.Conn().Exec(
-		"INSERT INTO notifications_sent (rgid) VALUES (?)",
+		"INSERT OR IGNORE INTO notifications_sent (rgid) VALUES (?)",
 		rgid,
 	)
 	if err != nil {
+		var sqliteErr sqlite3.Error
+		if errors.As(err, &sqliteErr) && sqliteErr.Code == sqlite3.ErrConstraint &&
+			sqliteErr.ExtendedCode == sqlite3.ErrConstraintForeignKey {
+			// Release row was pruned concurrently; nothing to mark.
+			return nil
+		}
 		return fmt.Errorf("mark notification sent: %w", err)
 	}
 	return nil
@@ -33,7 +54,7 @@ func IsNotificationSent(db *DB, rgid string) (bool, error) {
 // artists are excluded so the digest honors the monitoring contract.
 func GetUnnotifiedReleases(db *DB) ([]ExternalRelease, error) {
 	rows, err := db.Conn().Query(`
-		SELECT e.rgid, e.artist_id, e.title, e.type, e.release_date, e.is_ignored
+		SELECT e.rgid, e.artist_id, e.title, COALESCE(e.type,''), COALESCE(e.release_date,''), e.is_ignored
 		FROM external_releases e
 		JOIN artist_settings s ON e.artist_id = s.id
 		LEFT JOIN notifications_sent n ON e.rgid = n.rgid

internal/database/notifications_test.go

@@ -41,9 +41,38 @@ func TestMarkNotificationSent_New(t *testing.T) {
 	}
 }
 
-// TestMarkNotificationSent_DuplicateSecond verifies that inserting the same RGID twice
-// within the same second fails due to the composite primary key (rgid, sent_at).
-// In practice, notifications are sent at most once per day, so this is acceptable.
+// TestMarkNotificationSent_MissingReleaseIsNoOp verifies that marking a release
+// whose external_releases row does not exist (e.g. pruned by a concurrent
+// re-sync) does not error: the FK violation is swallowed by INSERT OR IGNORE so
+// a single vanished release cannot abort a digest's mark-sent loop.
+func TestMarkNotificationSent_MissingReleaseIsNoOp(t *testing.T) {
+	db, err := New(":memory:")
+	if err != nil {
+		t.Fatalf("New() error: %v", err)
+	}
+	defer db.Close()
+
+	// No artist/release inserted: rgid-gone has no external_releases row.
+	if err := MarkNotificationSent(db, "rgid-gone"); err != nil {
+		t.Fatalf("MarkNotificationSent() for missing release should be a no-op, got error: %v", err)
+	}
+
+	// Nothing should have been recorded (FK violation ignored, row skipped).
+	var count int
+	if err := db.Conn().QueryRow("SELECT COUNT(*) FROM notifications_sent WHERE rgid = ?", "rgid-gone").Scan(&count); err != nil {
+		t.Fatalf("count query error: %v", err)
+	}
+	if count != 0 {
+		t.Errorf("expected 0 notification rows for missing release, got %d", count)
+	}
+}
+
+// TestMarkNotificationSent_DuplicateSecond verifies that marking the same RGID
+// twice within the same second is an idempotent no-op (INSERT OR IGNORE) rather
+// than an error: a same-second collision on the composite primary key
+// (rgid, sent_at) must not abort a digest's mark-sent loop, since that would
+// leave later releases unmarked and cause duplicate notifications on the next
+// run. The marker's presence, not its exact timestamp, is what matters.
 func TestMarkNotificationSent_DuplicateSecond(t *testing.T) {
 	db, err := New(":memory:")
 	if err != nil {
@@ -60,10 +89,9 @@ func TestMarkNotificationSent_DuplicateSecond(t *testing.T) {
 	if err := MarkNotificationSent(db, "rgid-1"); err != nil {
 		t.Fatalf("first MarkNotificationSent() error: %v", err)
 	}
-	// Second insert in the same second should fail with a UNIQUE constraint error.
-	err = MarkNotificationSent(db, "rgid-1")
-	if err == nil {
-		t.Fatal("expected UNIQUE constraint error on duplicate insert, got nil")
+	// Second mark in the same second should be a silent no-op, not an error.
+	if err := MarkNotificationSent(db, "rgid-1"); err != nil {
+		t.Fatalf("duplicate MarkNotificationSent() should be a no-op, got error: %v", err)
 	}
 
 	// Should still have exactly one row.

internal/notifier/scheduler.go

@@ -93,9 +93,13 @@ func NotifyOnce(ctx context.Context, db *database.DB, sender Sender, cfg config.
 		return 0, fmt.Errorf("notifier: send digest: %w", err)
 	}
 
+	// The digest has already been delivered at this point. A failure to mark a
+	// single release must NOT abort the loop: doing so would leave later
+	// releases unmarked and cause them to be re-notified (duplicate digest) on
+	// the next run. Log and continue so every release in this batch is marked.
 	for _, m := range toNotify {
 		if err := database.MarkNotificationSent(db, m.RGID); err != nil {
-			return 0, fmt.Errorf("notifier: mark sent for %s: %w", m.RGID, err)
+			log.Printf("notifier: mark sent for %s failed: %v", m.RGID, err)
 		}
 	}
 	return len(toNotify), nil