-- AlterTable
ALTER TABLE "users" ADD COLUMN "invite_code" VARCHAR(16);

-- Backfill existing admins and agents with deterministic unique codes
UPDATE "users"
SET "invite_code" = UPPER(SUBSTR(MD5("id"::text || ':invite'), 1, 8))
WHERE "user_type" IN ('ADMIN', 'AGENT')
  AND "invite_code" IS NULL;

-- CreateIndex
CREATE UNIQUE INDEX "users_invite_code_key" ON "users"("invite_code");