feat(server): library_changes log table + sqlc queries

Append-only change log for library entities. Every mutation on
artists/albums/tracks/likes/playlists/playlist_tracks will write a row
in the same transaction as the mutation itself (wired in subsequent
commits). Powers the Flutter delta-sync endpoint (#357).

- 0025_library_changes migration (up + down)
- internal/db/queries/library_changes.sql (Insert, GetSince, MaxCursor, MinCursor)
- regenerated dbq from sqlc

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/db/dbq/library_changes.sql.go

@@ -0,0 +1,87 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.31.1
+// source: library_changes.sql
+
+package dbq
+
+import (
+	"context"
+)
+
+const getLibraryChangesSince = `-- name: GetLibraryChangesSince :many
+SELECT id, entity_type, entity_id, op, changed_at
+FROM library_changes
+WHERE id > $1
+ORDER BY id ASC
+LIMIT $2
+`
+
+type GetLibraryChangesSinceParams struct {
+	ID    int64
+	Limit int32
+}
+
+func (q *Queries) GetLibraryChangesSince(ctx context.Context, arg GetLibraryChangesSinceParams) ([]LibraryChange, error) {
+	rows, err := q.db.Query(ctx, getLibraryChangesSince, arg.ID, arg.Limit)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []LibraryChange
+	for rows.Next() {
+		var i LibraryChange
+		if err := rows.Scan(
+			&i.ID,
+			&i.EntityType,
+			&i.EntityID,
+			&i.Op,
+			&i.ChangedAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const getMaxLibraryChangeCursor = `-- name: GetMaxLibraryChangeCursor :one
+SELECT COALESCE(MAX(id), 0)::BIGINT FROM library_changes
+`
+
+func (q *Queries) GetMaxLibraryChangeCursor(ctx context.Context) (int64, error) {
+	row := q.db.QueryRow(ctx, getMaxLibraryChangeCursor)
+	var column_1 int64
+	err := row.Scan(&column_1)
+	return column_1, err
+}
+
+const getMinLibraryChangeCursor = `-- name: GetMinLibraryChangeCursor :one
+SELECT COALESCE(MIN(id), 0)::BIGINT FROM library_changes
+`
+
+func (q *Queries) GetMinLibraryChangeCursor(ctx context.Context) (int64, error) {
+	row := q.db.QueryRow(ctx, getMinLibraryChangeCursor)
+	var column_1 int64
+	err := row.Scan(&column_1)
+	return column_1, err
+}
+
+const insertLibraryChange = `-- name: InsertLibraryChange :exec
+INSERT INTO library_changes (entity_type, entity_id, op)
+VALUES ($1, $2, $3)
+`
+
+type InsertLibraryChangeParams struct {
+	EntityType string
+	EntityID   string
+	Op         string
+}
+
+func (q *Queries) InsertLibraryChange(ctx context.Context, arg InsertLibraryChangeParams) error {
+	_, err := q.db.Exec(ctx, insertLibraryChange, arg.EntityType, arg.EntityID, arg.Op)
+	return err
+}

internal/db/dbq/models.go

@@ -283,6 +283,14 @@ type GeneralLikesArtist struct {
 	LikedAt  pgtype.Timestamptz
 }
 
+type LibraryChange struct {
+	ID         int64
+	EntityType string
+	EntityID   string
+	Op         string
+	ChangedAt  pgtype.Timestamptz
+}
+
 type LidarrConfig struct {
 	ID                       int16
 	Enabled                  bool

internal/db/migrations/0025_library_changes.down.sql

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

internal/db/migrations/0025_library_changes.up.sql

@@ -0,0 +1,23 @@
+-- Append-only change log for library entities. Every mutation on
+-- artists/albums/tracks/likes/playlists/playlist_tracks writes a row
+-- in the same transaction as the mutation itself. Powers the Flutter
+-- delta-sync endpoint (#357) — clients pass back the last-seen `id`
+-- as a cursor.
+--
+-- Retention: not capped here. If the table grows unbounded a follow-up
+-- adds a periodic compactor (collapse contiguous upserts on the same
+-- entity, drop pre-delete history). Cursor reset path (410) covers the
+-- compactor's edge.
+
+CREATE TABLE library_changes (
+  id BIGSERIAL PRIMARY KEY,
+  entity_type TEXT NOT NULL CHECK (entity_type IN (
+    'artist', 'album', 'track', 'like_track', 'like_album', 'like_artist',
+    'playlist', 'playlist_track'
+  )),
+  entity_id TEXT NOT NULL,
+  op TEXT NOT NULL CHECK (op IN ('upsert', 'delete')),
+  changed_at TIMESTAMPTZ NOT NULL DEFAULT now()
+);
+
+CREATE INDEX idx_library_changes_id ON library_changes(id);

internal/db/queries/library_changes.sql

@@ -0,0 +1,16 @@
+-- name: InsertLibraryChange :exec
+INSERT INTO library_changes (entity_type, entity_id, op)
+VALUES ($1, $2, $3);
+
+-- name: GetLibraryChangesSince :many
+SELECT id, entity_type, entity_id, op, changed_at
+FROM library_changes
+WHERE id > $1
+ORDER BY id ASC
+LIMIT $2;
+
+-- name: GetMaxLibraryChangeCursor :one
+SELECT COALESCE(MAX(id), 0)::BIGINT FROM library_changes;
+
+-- name: GetMinLibraryChangeCursor :one
+SELECT COALESCE(MIN(id), 0)::BIGINT FROM library_changes;