libuvcpp: move the pin to 1.7.2-dev, and answer the JSON profiles with the framework's standard serializer

frameworks/libuvcpp/compose.gateway-h3.yml

@@ -1,11 +1,14 @@
 # gateway-h3 — the same two-service stack as compose.gateway.yml, exercised
 # over HTTP/3 at the edge.
 #
-# Nothing about the stack changes: stock Caddy binds 8443 on both tcp and udp
-# from the same `protocols h1 h2 h3` server block, so the proxy config is
-# byte-identical and only the load generator differs (h2load with
-# `--alpn-list=h3`). The upstream hop stays plain h1 over loopback, which is
-# what the server speaks.
+# Same shape, same backend, same upstream hop (plain h1 over loopback), and a
+# different edge *image*: this one is stock Caddy from ./proxy-h3, where
+# gateway-64 is stock nginx from ./proxy. The split exists because h3 needs
+# QUIC and nginx has no HTTP/3 without a custom build against a QUIC library,
+# while over the profile's h1 upstream hop Caddy costs ~3x nginx per request at
+# gateway-64's multiplexing -- so the two profiles want different edges. Caddy
+# binds 8443 on both tcp and udp from its `protocols h1 h2 h3` server block,
+# and the h3 load generator reaches the udp half (h2load with `--alpn-list=h3`).
 #
 # Kept as a separate file rather than a symlink because the harness resolves
 # compose files by name (`compose.<profile>.yml`, with gateway-64 on the legacy
@@ -21,7 +24,7 @@
 services:
   proxy:
     build:
-      context: ./proxy
+      context: ./proxy-h3
     network_mode: host
     cpuset: "${PROXY_CPUSET:-0-15,64-79}"
     ulimits:

frameworks/libuvcpp/compose.gateway.yml

@@ -1,10 +1,16 @@
-# gateway-64 — stock Caddy (TLS + h2 on 8443) in front of the libuvcpp server.
+# gateway-64 — stock nginx (TLS + h2 on 8443) in front of the libuvcpp server.
 #
 # Two services, which is what the profile fixes: `proxy` terminates TLS, serves
 # /static/* off disk and forwards the dynamic endpoints over plain h1 to
 # 127.0.0.1:8085; `server` answers /baseline2, /json/{n} and /async-db and
 # nothing else.
 #
+# The edge is nginx rather than the Caddy that gateway-h3 still uses, because at
+# this profile's 512 connections x 32 streams Caddy costs ~3x nginx per request
+# over an h1 upstream and the proxy was therefore the stack's bottleneck (96% of
+# its 32 CPUs against the server's 23%). proxy/nginx.conf has the measurement.
+# The h3 profile cannot follow: h3 needs QUIC, which nginx lacks.
+#
 # The server is deliberately **not** given /certs. main.cc opens its 8081 and
 # 8443 listeners only when the certificate pair is readable, so with no certs
 # mounted it comes up on its two cleartext ports alone and leaves every TLS port

frameworks/libuvcpp/compose.production-stack.yml

@@ -1,7 +1,7 @@
 # production-stack — edge + cache + authsvc + server, four services on a 64
 # logical CPU budget.
 #
-#   edge     (caddy)     30 logical CPUs. TLS + h2 termination, /static served
+#   edge     (nginx)     30 logical CPUs. TLS + h2 termination, /static served
 #                        off disk, one auth subrequest per /api/* call.
 #   cache    (redis)      2. Redis is single-threaded on the data path; a
 #                        second core would sit idle.
@@ -14,6 +14,13 @@
 # All four on host networking, so what passes between them is loopback: the
 # edge owns 8443, authsvc 9090, the server 8085, the cache 6379.
 #
+# The edge is nginx rather than the Caddy this stack used before. The profile's
+# own architecture diagram names nginx and `auth_request`, and on a 4-core
+# stand-in for this shape Caddy's edge cost 392-440 us of CPU per request
+# against nginx's 101, with the edge pinned at its core budget in every arm.
+# proxy-production/nginx.conf carries the measurement. Nothing here is h3, so
+# unlike the gateway pair this stack does not need a Caddy twin.
+#
 # The server is not given /certs, for the same reason as the gateway stacks --
 # main.cc opens its TLS listeners only when the certificate pair is readable, so
 # without it the server stays on its two cleartext ports and the edge has 8443