local-instance: raise the proxy's header buffers, or topic pages 502

A topic page makes the legacy client set several large cookies at once —
jwt plus the Etherpad session it asks for — which overflows nginx's default
4k header buffer. The upstream answered 200 and the proxy still returned 502
with "upstream sent too big header".

It went unnoticed because the MCP server's topic-page scrape degrades to an
empty list by design: the task ids it recovers from that page silently
vanished instead of failing. Changed in the generator and in the generated
config.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

local-instance/scripts/gen-proxy-conf.py

@@ -76,6 +76,17 @@ server {
 	proxy_read_timeout 300s;
 	proxy_send_timeout 300s;
 
+	# The legacy client sets several large cookies at once (jwt plus the
+	# Etherpad session it requests on every topic page), which overflows
+	# nginx's default 4k header buffer: the upstream answers 200 and the proxy
+	# still returns 502 with "upstream sent too big header". Topic pages are
+	# the visible casualty, and because the MCP server's topic-page scrape
+	# degrades to an empty list by design, the ids it recovers just silently
+	# vanish rather than erroring.
+	proxy_buffer_size 32k;
+	proxy_buffers 8 32k;
+	proxy_busy_buffers_size 64k;
+
 	# version-aggregator-svc upstream; /serverversion and /nuxtversion are the
 	# real per-app endpoints and are routed below.
 	location = /version {