diff --git a/.railway/README.md b/.railway/README.md
index 6476535..ec92b6e 100644
--- a/.railway/README.md
+++ b/.railway/README.md
@@ -16,7 +16,8 @@ railway config apply
 - **Partial `web`.** The file owns only the web service. Postgres, its volume,
   and slack-cards are not in it and apply never touches them.
 - **Variables.** Every value stays in Railway; the file marks each one
-  `preserve()`. Never put a secret here.
+  `preserve()`. Never put a secret here. **Add every new web variable to the
+  file as `preserve()`**: apply deletes any variable the file leaves out.
 - **Node version.** `RAILPACK_NODE_VERSION` comes from `../.nvmrc`. Railpack
   reads that variable before `package.json` engines, so it decides the Node a
   deploy runs. To apply everything except a Node change, set
diff --git a/.railway/railway.ts b/.railway/railway.ts
index 89722cc..c87c457 100644
--- a/.railway/railway.ts
+++ b/.railway/railway.ts
@@ -45,6 +45,7 @@ export default defineRailway((ctx) => {
     replicas: { "us-east4-eqdc4a": 1 },
     domains: env.domains.map((domain) => ({ domain, port: 3000 })),
     // Values live in Railway, never in this file. preserve() keeps each one.
+    // Every variable on web must be listed here: apply deletes any it omits.
     env: {
       APP_BASE_URL: preserve(),
       APP_ENV: preserve(),
@@ -57,6 +58,7 @@ export default defineRailway((ctx) => {
       RELAY_API_KEY: preserve(),
       RELAY_BASE_URL: preserve(),
       RELAY_CONNECT_PRODUCT: preserve(),
+      RELAY_INBOUND_SECRET: preserve(),
       RELAY_WEBHOOK_SECRET: preserve(),
       SESSION_SECRET: preserve(),
       STORE_BASE_URL: preserve(),