perf: bound request work and resource usage (#866)

* perf: bound request work and resource usage

* fix: address performance review regressions

* fix: guard content expiration and dashboard state

* fix: tolerate cache outages and retire derived paths

* fix: revalidate expiration claims and status pagination

* fix: retry interrupted repository metadata cleanup

* fix: retire obsolete content cache storage

* fix: activate tree metadata and recheck expiration claims

* fix: fence cache publication across expiration

* fix: recover staged trees and enforce cache lifecycle cleanup

* fix: prune expired transforms during database outages

* fix: finish conference removals and reload expiration candidates

test/fixtures/performance-streamer.js

@@ -0,0 +1,42 @@
+const { Readable } = require("node:stream");
+const path = require("node:path");
+const compiled = process.env.PERFORMANCE_STREAMER_COMPILED === "1";
+if (!compiled) require("ts-node/register/transpile-only");
+const base = path.join(__dirname, compiled ? "../../build" : "../../src");
+const GitHubStream = require(path.join(base, "core/source/GitHubStream")).default;
+const FileSystem = require(path.join(base, "core/storage/FileSystem")).default;
+const maintenance = require(path.join(base, "core/temporary-storage"));
+const startMaintenance = maintenance.startTemporaryStorageMaintenance;
+// Exercise the real startup/timer wiring without waiting a production minute.
+maintenance.startTemporaryStorageMaintenance = () => startMaintenance(25);
+GitHubStream.prototype.downloadWithFallback = async function () {
+  process.send({ download: true });
+  return Readable.from([Buffer.alloc(300000, "x")]);
+};
+const write = FileSystem.prototype.write;
+let release, releaseConnection;
+if (process.env.PERFORMANCE_HOLD_CONNECT === "1") {
+  const database = require(path.join(base, "server/database")), connect = database.connect;
+  database.connect = async (...args) => {
+    const held = new Promise(resolve => { releaseConnection = resolve; });
+    process.send({ connectionHeld: true }); await held;
+    return connect(...args);
+  };
+}
+FileSystem.prototype.write = async function (...args) {
+  if (args[1].endsWith("/hold.txt")) {
+    const held = new Promise(resolve => { release = resolve; });
+    process.send({ held: true }); await held;
+  }
+  return write.apply(this, args);
+};
+if (process.env.CREDENTIAL_KEYS !== "invalid") process.on("message", message => {
+  if (message === "release") release?.();
+  if (message === "connect") releaseConnection?.();
+  if (message === "inspect") {
+    const options = require("mongoose").connection.getClient().options;
+    process.send({ connected: require(path.join(base, "server/database")).isConnected,
+      maxPoolSize: options.maxPoolSize, minPoolSize: options.minPoolSize });
+  }
+});
+require(path.join(base, "streamer/index"));