feat(api): give every error envelope a meta.errorCode

Roughly half of the refusals answered prose alone, so a client could branch
on the code for one 404 and had to fall back to the status for the next.
apiHandler now completes every error envelope with the status's generic
http.* code when the route named none; a route's own code still wins. The
family joins the published catalogue, and the profile form only shows a
code's sentence when the code has one.

src/lib/api-handler.ts

@@ -55,7 +55,7 @@ import {
 } from "./sharing/record-session-fence";
 import { refuseOnKeyMismatch } from "./boot/key-mismatch-refusal";
 import { acceptIncomingRequestId } from "./http/request-id";
-import { withErrorRequestId } from "./api-response";
+import { withErrorEnvelopeDefaults } from "./api-response";
 import {
   capturedRateLimit,
   rateLimitResponseHeaders,
@@ -365,9 +365,10 @@ export function apiHandler<T extends (...args: any[]) => Promise<Response>>(
           }
         }
         // Every error envelope names its request id in `meta.requestId`, so
-        // the id survives a proxy that strips the header (see
-        // `withErrorRequestId`).
-        const nr = (await withErrorRequestId(
+        // the id survives a proxy that strips the header, and carries a
+        // `meta.errorCode`, the status's default when the route named none
+        // (see `withErrorEnvelopeDefaults`).
+        const nr = (await withErrorEnvelopeDefaults(
           response as Response,
           evt.getRequestId(),
         )) as NextResponse;