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+/**
+ * Reconcile-historical-add-scripts convoy — Brief 2.
+ *
+ * Backfills the `collections`-table columns that historical scripts added to
+ * prod but which `migrations/1779853647564_initial-schema.js` never captured:
+ *
+ *   - `visibility VARCHAR(20) DEFAULT 'private'`  (from `scripts/add-collaboration-features.js`, lines 15-21 — collections half only)
+ *   - `tcg VARCHAR(50) DEFAULT 'MTG'`             (from `scripts/add-collaboration-features.js`, lines 15-21 — collections half only)
+ *   - `tags TEXT`                                 (from `scripts/add-collaboration-features.js`, lines 15-21 — collections half only)
+ *   - `slug VARCHAR(100) UNIQUE`                  (from `scripts/add-collection-slugs.js`, lines 17-20)
+ *   - `idx_collections_slug` UNIQUE INDEX         (from `scripts/add-collection-slugs.js`, line 79)
+ *   - `check_slug_format` CHECK constraint        (from `scripts/add-collection-slugs.js`, line 91)
+ *   - `image TEXT`                                (from `scripts/add-image-column.js`, lines 14-17)
+ *
+ * Excluded from B2 (out of scope per architect inventory):
+ *   - `collection_permissions`, `collection_activity`, `users.is_pending`,
+ *     `idx_collections_visibility`, `idx_collection_permissions_*`,
+ *     `idx_collection_activity_collection_id` — these belong to B3
+ *     (`reconcile-collaboration-tables`) per the architect plan.
+ *   - `is_system_collection` — already captured by
+ *     `migrations/1780378340194_system-collection-description.js`.
+ *
+ * Excluded DML: per-row UPDATE that backfills slugs from `name` via
+ * `lib/slug-utils.js::generateUniqueSlug` (script lines 41-74). Generating
+ * slugs on a fresh env is moot — there are no pre-existing collections to
+ * backfill — and replicating the runtime helper inside a migration would
+ * couple the schema timeline to application code. Operators of long-lived
+ * envs already ran the backfill historically; this migration does NOT
+ * re-run it.
+ *
+ * Idempotency strategy (D2): every statement is `IF NOT EXISTS`-guarded.
+ *
+ *   - `ADD COLUMN IF NOT EXISTS` — Postgres native; the `UNIQUE` inline
+ *     clause on `slug` is ignored when the column already exists, so prod
+ *     (which already has the autogen `collections_slug_key` constraint)
+ *     and fresh envs (where the autogen constraint will be added) both
+ *     converge correctly.
+ *   - `CREATE UNIQUE INDEX IF NOT EXISTS` — Postgres native.
+ *   - `ALTER TABLE ... ADD CONSTRAINT` for CHECK — Postgres has no
+ *     `IF NOT EXISTS` clause for named constraints, so we wrap in a
+ *     `DO $$ BEGIN ... END $$` block that checks `pg_constraint` first.
+ *
+ * Down-migration is a hard stub. See `down()` below — matches
+ * `1779853647564_initial-schema.js` style.
+ *
+ * @type {import('node-pg-migrate').ColumnDefinitions | undefined}
+ */
+export const shorthands = undefined;
+
+/**
+ * @param {import('node-pg-migrate').MigrationBuilder} pgm
+ * @returns {void}
+ */
+export const up = (pgm) => {
+  pgm.sql(`
+    ALTER TABLE collections
+      ADD COLUMN IF NOT EXISTS visibility VARCHAR(20) DEFAULT 'private',
+      ADD COLUMN IF NOT EXISTS tcg VARCHAR(50) DEFAULT 'MTG',
+      ADD COLUMN IF NOT EXISTS tags TEXT
+  `);
+
+  pgm.sql(`
+    ALTER TABLE collections
+      ADD COLUMN IF NOT EXISTS image TEXT
+  `);
+
+  pgm.sql(`
+    ALTER TABLE collections
+      ADD COLUMN IF NOT EXISTS slug VARCHAR(100) UNIQUE
+  `);
+
+  pgm.sql(`
+    CREATE UNIQUE INDEX IF NOT EXISTS idx_collections_slug
+      ON collections(slug)
+  `);
+
+  pgm.sql(`
+    DO $$
+    BEGIN
+      IF NOT EXISTS (
+        SELECT 1
+        FROM pg_constraint
+        WHERE conname = 'check_slug_format'
+          AND conrelid = 'collections'::regclass
+      ) THEN
+        ALTER TABLE collections
+          ADD CONSTRAINT check_slug_format
+          CHECK (slug ~ '^[a-z0-9]([a-z0-9-]*[a-z0-9])?$' AND length(slug) <= 50);
+      END IF;
+    END
+    $$;
+  `);
+};
+
+/**
+ * Down-migration is a hard stub. This is a reconciliation migration: the
+ * prod schema state is the source of truth, and dropping these columns
+ * would discard slugs / visibility flags / tcg labels / tags / images that
+ * application code reads on every collection page render. If you need a
+ * clean schema for testing, branch the Neon database and run
+ * `npm run migrate up` against the branch instead of rolling this back.
+ *
+ * @returns {void}
+ */
+export const down = () => {
+  throw new Error(
+    '[migration:1781000000002_reconcile-collections-columns] Refusing to drop reconciled columns. ' +
+      'Rolling back this migration would erase visibility/tcg/tags/slug/image data on every ' +
+      'collections row in the database. If you need a clean schema for testing, branch the ' +
+      'Neon database and run `npm run migrate up` against the branch instead. See ' +
+      'migrations/1781000000002_reconcile-collections-columns.js up() docstring for the ' +
+      'reconciliation rationale.'
+  );
+};