Performance trace, load test and chapter read-ahead

A switchable trace (DATA/perf/trace.on or PERF_TRACE=1) records every request's
phases (stat, open, first read, disk vs network wait), browser resource timings,
page-turn waits and flow stalls, a cold storage probe, event-loop lag, scans and
scraper calls as JSONL. tools/perf-report.js says which phase slow loads spend
their time in; tools/perf-bench.js simulates readers.

READ_AHEAD (default on) reads an opened chapter's pages, then the next chapter's,
into the OS cache so a NAS's cold reads stop reaching the browser.

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

test/dockerfile.test.js

@@ -3,6 +3,7 @@
 const test = require('node:test'), assert = require('node:assert/strict');
 const fs = require('fs'), path = require('path');
 const root = path.resolve(__dirname, '..');
+const allowedNames = () => new Set(fs.readFileSync(path.join(root, '.dockerignore'), 'utf8').split(/\r?\n/).filter(line => line.startsWith('!')).map(line => line.slice(1)));
 
 test('every top-level module the reader requires is copied into the image', () => {
   const dockerfile = fs.readFileSync(path.join(root, 'Dockerfile'), 'utf8');
@@ -12,14 +13,19 @@ test('every top-level module the reader requires is copied into the image', () =
     const file = pending.pop();
     if (seen.has(file)) continue;
     seen.add(file);
-    for (const [, name] of fs.readFileSync(path.join(root, file), 'utf8').matchAll(/require\('\.\/([\w.-]+?)(?:\.js)?'\)/g)) {
+    const source = fs.readFileSync(path.join(root, file), 'utf8');
+    for (const [, dir] of source.matchAll(/require\('\.\/([\w.-]+)\/[^']+'\)/g)) {
+      assert.ok(copied.has(dir), `${dir}/ is not copied`);
+      assert.ok(allowedNames().has(dir + '/'), `${dir}/ is not allowed through .dockerignore`);
+    }
+    for (const [, name] of source.matchAll(/require\('\.\/([\w.-]+?)(?:\.js)?'\)/g)) {
       // A folder (e.g. ./greatest) is copied as a whole; only single files need their own name in COPY.
       if (fs.existsSync(path.join(root, name)) && fs.statSync(path.join(root, name)).isDirectory()) assert.ok(copied.has(name), `${name}/ is not copied`);
       else pending.push(name + '.js');
     }
   }
   // .dockerignore is an allowlist too: a file not let through never reaches COPY.
-  const allowed = new Set(fs.readFileSync(path.join(root, '.dockerignore'), 'utf8').split(/\r?\n/).filter(line => line.startsWith('!')).map(line => line.slice(1)));
+  const allowed = allowedNames();
   for (const file of seen) {
     assert.ok(copied.has(file), `${file} is required but not copied by the Dockerfile`);
     assert.ok(allowed.has(file), `${file} is required but not allowed through .dockerignore`);