diff --git a/server/server/api/v1/client/auth/initiate.post.ts b/server/server/api/v1/client/auth/initiate.post.ts
index dddc71e6..fe55073c 100644
--- a/server/server/api/v1/client/auth/initiate.post.ts
+++ b/server/server/api/v1/client/auth/initiate.post.ts
@@ -18,6 +18,21 @@ const ClientAuthInitiate = type({
 }).configure(throwingArktype);
 
 export default defineEventHandler(async (h3) => {
+  // Version gate. Pre-0.4 desktop clients send no User-Agent (0.4+ sends
+  // "Drop Desktop Client" from the shared remote crate) and use a Nonce auth
+  // scheme this server no longer speaks. Without this check they pair
+  // successfully — the handshake is unauthenticated — and then every
+  // authenticated call 403s, which surfaces as an opaque "Unrecoverable
+  // error" after sign-in (zack.way, 2026-08-14). Failing here instead hits
+  // the old client's handshake error path, which DOES display `message`.
+  const userAgent = getHeader(h3, "User-Agent");
+  if (!userAgent)
+    throw createError({
+      statusCode: 400,
+      message:
+        "Your Drop client is too old for this server (it uses the pre-0.4 auth protocol). Download the current client from https://cdn.quasarke.net/drop-client/",
+    });
+
   const body = await readDropValidatedBody(h3, ClientAuthInitiate);
 
   const platformRaw = body.platform;
diff --git a/server/server/internal/clients/event-handler.ts b/server/server/internal/clients/event-handler.ts
index 103c7579..9295bd68 100644
--- a/server/server/internal/clients/event-handler.ts
+++ b/server/server/internal/clients/event-handler.ts
@@ -54,9 +54,16 @@ export function defineClientEventHandler<T>(handler: EventHandlerFunction<T>) {
         break;
       }
       default: {
+        // Pre-0.4 clients authenticate with a "Nonce ..." scheme this server
+        // no longer speaks. Their pairing handshake still succeeds (it is
+        // unauthenticated), so this is the first place they fail — and they
+        // render statusMessage, not message, so both carry the explanation.
         throw createError({
           statusCode: 403,
-          message: "No authentication",
+          statusMessage:
+            "Drop client too old for this server - get the current client at cdn.quasarke.net/drop-client",
+          message:
+            "Your Drop client is too old for this server (it uses the pre-0.4 auth protocol). Download the current client from https://cdn.quasarke.net/drop-client/",
         });
       }
     }