diff --git a/packages/server/src/test-utils/main-thread-work.ts b/packages/server/src/test-utils/main-thread-work.ts
index 66bb55e491..c823a96abd 100644
--- a/packages/server/src/test-utils/main-thread-work.ts
+++ b/packages/server/src/test-utils/main-thread-work.ts
@@ -24,6 +24,8 @@ export async function measureMainThreadWork<T>(label: string, action: () => T |
   let previousCpu = threadCpuUsage();
   let probe: ReturnType<typeof setInterval>;
   let drain: ReturnType<typeof setImmediate>;
+  const types = new Map<number, string>();
+  const stacks = new Map<number, string>();
   const callbacks = new Map<number, { wall: number; cpu: NodeJS.CpuUsage }>();
   const record = (wallMs: number, cpu: NodeJS.CpuUsage) => {
     const cpuMs = (cpu.user + cpu.system) / 1_000;
@@ -46,6 +48,10 @@ export async function measureMainThreadWork<T>(label: string, action: () => T |
   gc.observe({ entryTypes: ["gc"] });
   const activity = createHook({
     init(_id, type) {
+      if (label === "project config main-thread work") {
+        types.set(_id, type);
+        stacks.set(_id, new Error().stack ?? "");
+      }
       if (type.startsWith("FSREQ")) filesystemRequests++;
       if (!draining && type === "Immediate") yields++;
       if (type === "WORKER") workerEvents++;
@@ -60,7 +66,13 @@ export async function measureMainThreadWork<T>(label: string, action: () => T |
       const start = callbacks.get(id);
       if (!start) return;
       callbacks.delete(id);
-      record(performance.now() - start.wall, threadCpuUsage(start.cpu));
+      const wall = performance.now() - start.wall;
+      record(wall, threadCpuUsage(start.cpu));
+      if (wall > 10 && label === "project config main-thread work") {
+        process.stderr.write(
+          JSON.stringify({ wall, type: types.get(id), stack: stacks.get(id) }) + "\n",
+        );
+      }
     },
   }).enable();
   const sample = () => {
diff --git a/packages/server/src/utils/paseo-config-file.test.ts b/packages/server/src/utils/paseo-config-file.test.ts
index 186a5259ed..176c5754be 100644
--- a/packages/server/src/utils/paseo-config-file.test.ts
+++ b/packages/server/src/utils/paseo-config-file.test.ts
@@ -111,20 +111,23 @@ 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${i}`, { command: "echo hi" }]),
-      ),
-      worktree: { setup: "npm ci" },
-    };
-    await writeFile(join(tempDir, "paseo.json"), JSON.stringify(config));
-    const { result, blockingMs, filesystemRequests, yields } = await measureConfigRead(tempDir);
-    expect(result).toEqual({ ok: true, config, revision: await statPaseoConfigPath(tempDir) });
-    expect(blockingMs).toBeLessThan(20);
-    expect(filesystemRequests).toBeGreaterThan(0);
-    expect(yields).toBeGreaterThan(0);
-  });
+  it.each(Array.from({ length: 25 }, (_, i) => i))(
+    "keeps main-thread work below 20ms while admitting large configs (%i)",
+    async () => {
+      const config = {
+        scripts: Object.fromEntries(
+          Array.from({ length: 7_000 }, (_, i) => [`script${i}`, { command: "echo hi" }]),
+        ),
+        worktree: { setup: "npm ci" },
+      };
+      await writeFile(join(tempDir, "paseo.json"), JSON.stringify(config));
+      const { result, blockingMs, filesystemRequests, yields } = 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);
+    },
+  );
 
   it("rejects a 32MiB config with main-thread work below 20ms", async () => {
     await writeFile(