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-cache-worker.js

@@ -0,0 +1,23 @@
+const process = require("node:process");
+const { Readable } = require("node:stream");
+const { setTimeout: delay } = require("node:timers/promises");
+require("ts-node/register/transpile-only");
+const GitHubStream = require("../../src/core/source/GitHubStream").default;
+const source = new GitHubStream({ repoId: "replicas", organization: "owner", repoName: "repo", commit: "commit",
+  cacheGeneration: process.env.TEST_GENERATION || "generation1", getToken: () => "token" });
+source.downloadWithFallback = async () => {
+  process.send({ producer: true });
+  return Readable.from((async function* () {
+    yield Buffer.from("complete "); await delay(200); yield Buffer.from("content");
+  })());
+};
+process.once("message", async () => {
+  try {
+    const contents = await Promise.all(Array.from({ length: 5 }, async () => {
+      const input = await source.getFileContentCache("file.txt", "replicas", () => ({ sha: "blob", size: 16 }));
+      let text = ""; for await (const chunk of input) text += chunk; return text;
+    }));
+    process.send({ contents }); process.exit(0);
+  } catch (error) { process.send({ error: error.message }); process.exit(1); }
+});
+process.send({ ready: true });