withdraw-lock: refuse external sends when /locks/<type>.locked is present

Out-of-band emergency stop. The companion nobal.sh creates a sentinel
file on the host (bind-mounted at /locks in the container) when a
wallet balance drops below its failsafe threshold; debit() checks for
the file on every external send and refuses with "External withdrawals
temporarily disabled". /locks/ALL.locked is a global override.

Lives outside the db so a db-write vector (the May 18 /gateway pattern)
can't disable it. Internal sends are exempt — receives and user-to-user
transfers keep working with the site fully online during a lock.

For bitcoin and liquid this is a secondary defense on top of daemon-
level walletpassphrase rotation. For lightning, it's the only available
mechanism since CLN has no walletlock equivalent.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

1 files changed, 25 insertions, 0 deletions

diff --git a/lib/payments.ts b/lib/payments.ts
index 380b5e7b..01492975 100644
--- a/lib/payments.ts
+++ b/lib/payments.ts
@@ -1,6 +1,21 @@
 import config from "$config";
+import { existsSync } from "fs";
 import api from "$lib/api";
 import { archive, db, g, ga, gf, s, sa } from "$lib/db";
+
+// External-withdrawal lockfiles. Out-of-band emergency stop: nobal.sh (or a
+// human) can `touch /home/adam/locks/<type>.locked` on the host, which is
+// bind-mounted into this container at /locks. Existence of /locks/<type>.locked
+// (or /locks/ALL.locked) blocks all external sends of that type. Lives outside
+// db so it can't be disabled by a db-write vector (May 18 /gateway lesson).
+//
+// Internal payments are never blocked by these — receives and internal
+// transfers between coinos users keep working with the site fully online.
+const isWithdrawLocked = (type: string): string | null => {
+  if (existsSync("/locks/ALL.locked")) return "ALL";
+  if (existsSync(`/locks/${type}.locked`)) return type;
+  return null;
+};
 import { generate } from "$lib/invoices";
 import ln from "$lib/ln";
 import { err, l, warn } from "$lib/logging";
@@ -102,6 +117,16 @@ export const debit = async ({
     (await g("hardfreeze")) ||
     ((await g("freeze")) && type !== PaymentType.internal);
 
+  // Out-of-band withdrawal lock (file-based, can't be defeated by db writes).
+  // Internal sends are exempt — they don't touch external wallets.
+  if (type !== PaymentType.internal) {
+    const lockedKind = isWithdrawLocked(type);
+    if (lockedKind) {
+      warn("Blocking", user.username, amount, hash, user.id, type, "withdraw-lock", lockedKind);
+      fail("External withdrawals temporarily disabled");
+    }
+  }
+
   if (frozen || (amount > userLimit && !whitelisted)) {
     warn("Blocking", user.username, amount, hash, user.id, type, frozen, userLimit);
     fail("Problem sending payment");