docs: shorten cache interceptor comments

Addresses review feedback by trimming the stale-if-error comments to
terse one-liners in line with the surrounding interceptor style;
comment-only, no logic change.

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

Author: jeswr

lib/handler/cache-revalidation-handler.js

@@ -109,11 +109,8 @@ class CacheRevalidationHandler {
     }
 
     if (this.#callback) {
-      // If the response hasn't started yet and we're within the
-      //  stale-if-error threshold, serve the stale cached response instead
-      //  of failing the request. RFC 5861 defines an error as "any situation
-      //  that would result in a 500, 502, 503, or 504 HTTP response status
-      //  code being returned", which includes failing to reach the origin.
+      // Serve the stale cached response on a connection error, per stale-if-error:
+      //  RFC 5861 counts an unreachable origin (a would-be 5xx) as an error.
       // https://datatracker.ietf.org/doc/html/rfc5861#section-4
       if (this.#allowErrorStatusCodes) {
         this.#successful = true

test/interceptors/cache.js

@@ -862,10 +862,7 @@ describe('Cache Interceptor', () => {
 
     clock.tick(15000)
 
-    // Send second request. The response is stale and the origin is
-    //  unreachable, but we're within the stale-if-error threshold so the
-    //  stale response should still be served.
-    //  https://datatracker.ietf.org/doc/html/rfc5861#section-4
+    // Stale response, origin unreachable, but within stale-if-error: still served.
     {
       const response = await client.request(request)
       equal(requestsToOrigin, 1)
@@ -1561,9 +1558,7 @@ describe('Cache Interceptor', () => {
 
       clock.tick(15000)
 
-      // Send second request. The response is stale and the origin is
-      //  unreachable, but the request allows stale-if-error so the stale
-      //  response should still be served.
+      // Stale response, origin unreachable, but request allows stale-if-error: still served.
       {
         const response = await client.request({
           origin: 'localhost',