feat: add plan stacking

apps/api/src/db.ts

@@ -60,6 +60,7 @@ export async function migrate() {
 
   await sql`ALTER TABLE accounts ADD COLUMN IF NOT EXISTS plan TEXT NOT NULL DEFAULT 'free'`;
   await sql`ALTER TABLE accounts ADD COLUMN IF NOT EXISTS plan_expires_at TIMESTAMPTZ`;
+  await sql`ALTER TABLE accounts ADD COLUMN IF NOT EXISTS plan_stack JSONB NOT NULL DEFAULT '[]'`;
 
   await sql`CREATE INDEX IF NOT EXISTS idx_pings_monitor ON pings(monitor_id, checked_at DESC)`;
   await sql`CREATE INDEX IF NOT EXISTS idx_pings_checked_at ON pings(checked_at)`;

apps/api/src/routes/auth.ts

@@ -115,7 +115,7 @@ export const account = new Elysia({ prefix: "/account" })
   .use(requireAuth)
 
   .get("/settings", async ({ accountId }) => {
-    const [acc] = await sql`SELECT id, email_hash, plan, plan_expires_at, created_at FROM accounts WHERE id = ${accountId}`;
+    const [acc] = await sql`SELECT id, email_hash, plan, plan_expires_at, plan_stack, created_at FROM accounts WHERE id = ${accountId}`;
     const keys = await sql`SELECT id, key, label, created_at, last_used_at FROM api_keys WHERE account_id = ${accountId} ORDER BY created_at DESC`;
     const [{ count: monitorCount }] = await sql`SELECT COUNT(*)::int as count FROM monitors WHERE account_id = ${accountId}`;
     const limits = getPlanLimits(acc.plan);
@@ -124,6 +124,7 @@ export const account = new Elysia({ prefix: "/account" })
       has_email: !!acc.email_hash,
       plan: acc.plan,
       plan_expires_at: acc.plan_expires_at,
+      plan_stack: acc.plan_stack || [],
       monitor_count: monitorCount,
       limits,
       created_at: acc.created_at,

apps/api/src/utils/plans.ts

@@ -31,3 +31,12 @@ export const PRO_MULTIPLIERS = [
 
 export const PRO_MONTHLY_USD = 12;
 export const LIFETIME_USD = 140;
+
+// Tier ranking for plan stacking decisions
+const PLAN_RANK: Record<string, number> = {
+  free: 0, pro: 1, lifetime: 1, pro2x: 2, pro4x: 3,
+};
+
+export function planTier(plan: string): number {
+  return PLAN_RANK[plan] ?? 0;
+}