Say the proxy is covered by default or by a set value

The rate-limit test comments on trustedProxyCIDR and forwardedKeyFor
said production needs TRUSTED_PROXIES set; another said only
operator-listed addresses are trusted. The README's Rate Limiting
paragraph said "listed in", and the login endpoint section assumed
every proxied deployment shares one bucket. All now match the
RFC 1918 default.

Model: opus-5-5

README.md

@@ -2551,7 +2551,7 @@ arrived uncut — never the numbers.
 
 Every limiter here — receiver, login, and password change — identifies
 the client the same way, through one shared key function: the
-connection's own address, unless the peer is listed in
+connection's own address, unless the peer is inside
 `TRUSTED_PROXIES`, in which case the forwarded client address is used
 instead. That address becomes a bucket by family: IPv4 keys on the full
 address, IPv6 on its `/64` prefix. A routed `/64` is the normal
@@ -2589,7 +2589,8 @@ opposite directions:
 
 The login `POST` is the one endpoint with no pre-emptive limiter in
 front of it, and that is deliberate. A limiter that spends budget on
-arrival is a lockout in this deployment shape: sharing one bucket, a
+arrival is a lockout wherever clients share one bucket, as they do
+behind a reverse proxy that `TRUSTED_PROXIES` does not cover: a
 stranger sending five POSTs a minute — about 0.08 requests per second,
 from anywhere — keeps it permanently full, and the operator has no
 second administrative path. So the handler inverts the order:

internal/middleware/ratelimit_test.go

@@ -384,8 +384,8 @@ const (
 	// trustedProxyCIDR is the proxy network the forwarded-path
 	// tests configure, and trustedPeer an address inside it. A
 	// production deployment is required to run behind a reverse
-	// proxy with TRUSTED_PROXIES set, so this is the shape the
-	// bucketing has to hold in.
+	// proxy that TRUSTED_PROXIES covers, either by the default or by
+	// a set value, so this is the shape the bucketing has to hold in.
 	trustedProxyCIDR = "10.0.0.0/8"
 	trustedPeer      = "10.0.0.1:44444"
 )
@@ -1097,8 +1097,9 @@ func TestPostRateLimit_IPv4IndependentPerAddress(t *testing.T) {
 // that arrives from trustedPeer — a configured trusted proxy — and
 // names forwarded as its client in X-Forwarded-For. That is the
 // production path: a deployment is required to run behind a reverse
-// proxy with TRUSTED_PROXIES set, so the forwarded address, not the
-// peer, is what the limiters bucket on there.
+// proxy that TRUSTED_PROXIES covers, either by the default or by a
+// set value, so the forwarded address, not the peer, is what the
+// limiters bucket on there.
 func forwardedKeyFor(
 	t *testing.T, m *middleware.Middleware, forwarded string,
 ) string {
@@ -1178,9 +1179,9 @@ func TestRateLimitKey_ForwardedIPv6BucketsByPrefix(t *testing.T) {
 //
 // Every existing test of this fallback uses an IPv4 proxy, where
 // bucketKey is the identity function, so replacing the call with
-// peer.String() leaves the whole suite green. Only operator-listed
-// addresses reach this line and the fallback is fail-closed, so this
-// pins behaviour rather than fixing a defect.
+// peer.String() leaves the whole suite green. Only addresses inside
+// TRUSTED_PROXIES reach this line and the fallback is fail-closed, so
+// this pins behaviour rather than fixing a defect.
 func TestRateLimitKey_TrustedPeerUnusableForwardedMasksPeer(
 	t *testing.T,
 ) {