Stop Autumn-only code paths throwing in local-ledger billing mode

Two call sites still hard-required AUTUMN_SECRET_KEY regardless of billing
mode: the /api/autumn/$ route (autumn-js's client-side hooks hit it after
sign-up/on billing screens) and getBillingUsageEvents (Autumn's per-event
usage history). Both now degrade gracefully — 404 and an empty list,
respectively — when Autumn isn't configured, the same way subscription.ts's
credit checks already do, instead of autumn-js throwing "secret key not
found" once a request actually reaches it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/routes/api/autumn/$.ts

@@ -53,7 +53,13 @@ function loadHandler() {
 }
 
 async function handleAutumnRequest(request: Request) {
-  if (!isHostedAuthMode(env.AUTH_MODE)) {
+  // 404 in non-hosted modes, and also in hosted mode when Autumn isn't
+  // configured — a direct-Stripe deployment runs the local-ledger billing
+  // fallback instead (see subscription.ts) and has no Autumn customer to
+  // read, so this route has nothing to serve. Checking here, before
+  // loadHandler(), avoids autumn-js throwing "secret key not found" deep
+  // inside the handler once a client request reaches it.
+  if (!isHostedAuthMode(env.AUTH_MODE) || !env.AUTUMN_SECRET_KEY?.trim()) {
     return new Response("Not found", {
       status: 404,
     });

src/serverFunctions/billing.ts

@@ -6,6 +6,7 @@ import {
 } from "@/shared/billing";
 import { AppError } from "@/server/lib/errors";
 import {
+  getOptionalEnvValue,
   getRequiredEnvValue,
   isHostedServerAuthMode,
 } from "@/server/lib/runtime-env";
@@ -61,6 +62,13 @@ export const getBillingUsageEvents = createServerFn({ method: "POST" })
       return [];
     }
 
+    // No Autumn behind this deployment (local-ledger billing fallback, see
+    // subscription.ts) — there's no per-event usage history to page through,
+    // just the running total the ledger keeps.
+    if (!(await getOptionalEnvValue("AUTUMN_SECRET_KEY"))) {
+      return [];
+    }
+
     const events: BillingUsageEvent[] = [];
     let offset = 0;