fix(cf-function): guard against null metadata to prevent 502s

When the KV store returns null/undefined for the metadata key — which
can happen transiently during deployment as the KV entry propagates to
edge nodes — routeSite throws an uncaught TypeError accessing
metadata.base, causing CloudFront to return a 502.

This is most visible when errorPage is configured, because that disables
the function-level custom404 fallback in favour of distribution-level
customErrorResponses. The 502 manifests inconsistently because only
some edge nodes are affected during the propagation window.

The fix fails open: if metadata is unavailable, pass the request through
to the default origin unchanged rather than crashing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nicholasgubbins

platform/src/components/aws/ssr-site.ts

@@ -943,6 +943,7 @@ async function handler(event) {
     metadata = JSON.parse(v);
   } catch (e) {}
 
+  if (!metadata) return event.request;
   const response = await routeSite(kvNamespace, metadata);
   return response || event.request;
 }`,

platform/src/components/aws/static-site.ts

@@ -1129,6 +1129,7 @@ async function handler(event) {
     metadata = JSON.parse(v);
   } catch (e) {}
 
+  if (!metadata) return event.request;
   const response = await routeSite(kvNamespace, metadata);
   return response || event.request;
 }`,