From 14329d1b982c926111f15eb0afcd9a14b8a3a779 Mon Sep 17 00:00:00 2001
From: "paseo-bot[bot]" <266920839+paseo-bot[bot]@users.noreply.github.com>
Date: Fri, 30 Oct 2026 12:08:00 +0000
Subject: [PATCH] test(server): diagnose recurring config responsiveness
 failure

---
 .../src/utils/paseo-config-file.test.ts       | 35 ++++++++++---------
 .../test-fixtures/config-responsiveness.ts    | 23 ++++++++++++
 2 files changed, 42 insertions(+), 16 deletions(-)

diff --git a/packages/server/src/utils/paseo-config-file.test.ts b/packages/server/src/utils/paseo-config-file.test.ts
index 6a7e43c757..ae58676e8a 100644
--- a/packages/server/src/utils/paseo-config-file.test.ts
+++ b/packages/server/src/utils/paseo-config-file.test.ts
@@ -133,22 +133,25 @@ describe("paseo config file substrate", () => {
     expect(blockingMs).toBeLessThan(20);
   });
 
-  it("keeps main-thread work below 20ms while admitting large configs", async () => {
-    const config = {
-      scripts: Object.fromEntries(
-        Array.from({ length: 7_000 }, (_, i) => [`script${i}`, { command: "echo hi" }]),
-      ),
-      worktree: { setup: "npm ci" },
-    };
-    await writeFile(join(tempDir, "paseo.json"), JSON.stringify(config));
-    const { result, blockingMs, filesystemRequests, yields, workerMessages } =
-      await measureConfigRead(tempDir);
-    expect(result).toEqual({ ok: true, config, revision: await statPaseoConfigPath(tempDir) });
-    expect(blockingMs).toBeLessThan(20);
-    expect(filesystemRequests).toBeGreaterThan(0);
-    expect(yields).toBeGreaterThan(0);
-    expect(workerMessages).toBe(0);
-  });
+  it.each(Array.from({ length: 30 }, (_, i) => i))(
+    "keeps main-thread work below 20ms while admitting large configs (%i)",
+    async () => {
+      const config = {
+        scripts: Object.fromEntries(
+          Array.from({ length: 7_000 }, (_, i) => [`script${i}`, { command: "echo hi" }]),
+        ),
+        worktree: { setup: "npm ci" },
+      };
+      await writeFile(join(tempDir, "paseo.json"), JSON.stringify(config));
+      const { result, blockingMs, filesystemRequests, yields, workerMessages } =
+        await measureConfigRead(tempDir);
+      expect(result).toEqual({ ok: true, config, revision: await statPaseoConfigPath(tempDir) });
+      expect(blockingMs).toBeLessThan(20);
+      expect(filesystemRequests).toBeGreaterThan(0);
+      expect(yields).toBeGreaterThan(0);
+      expect(workerMessages).toBe(0);
+    },
+  );
 
   it("rejects a 32MiB config with main-thread work below 20ms", async () => {
     await writeFile(
diff --git a/packages/server/src/utils/test-fixtures/config-responsiveness.ts b/packages/server/src/utils/test-fixtures/config-responsiveness.ts
index 9e151c805a..8a7a731c8b 100644
--- a/packages/server/src/utils/test-fixtures/config-responsiveness.ts
+++ b/packages/server/src/utils/test-fixtures/config-responsiveness.ts
@@ -1,4 +1,5 @@
 import { createHook, executionAsyncResource } from "node:async_hooks";
+import { Session } from "node:inspector/promises";
 import { MessagePort } from "node:worker_threads";
 import assert from "node:assert/strict";
 import { setImmediate as nextTurn } from "node:timers/promises";
@@ -17,8 +18,30 @@ const activity = createHook({
     if (executionAsyncResource() instanceof MessagePort) workerMessages++;
   },
 }).enable();
+const profiler = new Session();
+profiler.connect();
+await profiler.post("Profiler.enable");
+await profiler.post("Profiler.setSamplingInterval", { interval: 100 });
+await profiler.post("Profiler.start");
 const measured = await measureMainThreadWork("project config main-thread work", () =>
   readPaseoConfigForEdit(directory),
 );
 activity.disable();
+const { profile } = await profiler.post("Profiler.stop");
+profiler.disconnect();
+if (measured.blockingMs >= 20) {
+  const nodes = new Map(profile.nodes.map((node) => [node.id, node]));
+  const samples = new Map<number, number>();
+  for (const [index, id] of (profile.samples ?? []).entries()) {
+    samples.set(id, (samples.get(id) ?? 0) + (profile.timeDeltas?.[index] ?? 0));
+  }
+  const hottest = [...samples]
+    .sort((a, b) => b[1] - a[1])
+    .slice(0, 20)
+    .map(([id, micros]) => {
+      const frame = nodes.get(id)!.callFrame;
+      return { function: frame.functionName, line: frame.lineNumber, milliseconds: micros / 1000 };
+    });
+  process.stderr.write(`Config CPU diagnostic: ${JSON.stringify(hottest)}\n`);
+}
 process.stdout.write(JSON.stringify({ ...measured, workerMessages }));