Compression across the board: directory answers, uploads, metrics, traces, the page (#253)

Measured 2026-10-16, uncompressed until now: the directory's answers (the feed list ipx reads,
603 KB of JSON, ~134 ms of a 159 ms Directory request), ipx's snapshot upload (~100 KB each half
hour), both /metrics (4.7 and 0.9 KB every 15 s) and every trace export to Tempo. Already
compressed: ipx-web's answers (zstd, #239), the home page and the directory's public pages
through Cloudflare (brotli, zstd).

- The directory compresses with brotli, zstd or gzip as asked, and unpacks a gzipped request.
- ipx sends its snapshot gzipped; the directory is deployed first.
- Both /metrics answer gzipped, as Prometheus asks.
- opentelemetry-otlp's gzip-http: OTEL_EXPORTER_OTLP_COMPRESSION=gzip compresses the export, set
  for all three in production's compose file; Caddy's exporter reads the same variable.
- web/build.mjs writes .br (quality 11) and .gz (level 9) beside each text file, and Caddy serves
  them in place (file_server precompressed): app.js 30 KB where zstd on the fly gave 37, app.css
  11 where 14. A .br or .gz asked for by name is refused, or /admin.js.br would be the admin
  page's script without the check that keeps it to admins; in a handle of its own, since a bare
  respond runs after the handles.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/build.mjs

@@ -12,6 +12,7 @@
 import crypto from 'node:crypto';
 import fs from 'node:fs';
 import path from 'node:path';
+import zlib from 'node:zlib';
 import { fileURLToPath } from 'node:url';
 import swc from '@swc/core';
 import html from '@swc/html';
@@ -113,4 +114,13 @@ if (process.argv[1] === fileURLToPath(import.meta.url)) {
     fs.writeFileSync(path.join(out, name), html);
     fs.writeFileSync(path.join(out, script), js);
   }
+  // Each text file compressed once here, as hard as it goes, brotli and gzip beside it, for Caddy
+  // to send in its place (#253): smaller than compressing each answer as it goes, and no work then.
+  for (const f of fs.readdirSync(out).filter(f => /\.(html|js|css|svg|txt)$/.test(f))) {
+    const body = fs.readFileSync(path.join(out, f));
+    fs.writeFileSync(path.join(out, f + '.br'), zlib.brotliCompressSync(body, {
+      params: { [zlib.constants.BROTLI_PARAM_QUALITY]: zlib.constants.BROTLI_MAX_QUALITY, [zlib.constants.BROTLI_PARAM_SIZE_HINT]: body.length },
+    }));
+    fs.writeFileSync(path.join(out, f + '.gz'), zlib.gzipSync(body, { level: 9 }));
+  }
 }