diff --git a/e2e/create-expert/create-expert.test.ts b/e2e/create-expert/create-expert.test.ts
index a7476995..3a6f0e23 100644
--- a/e2e/create-expert/create-expert.test.ts
+++ b/e2e/create-expert/create-expert.test.ts
@@ -66,6 +66,20 @@ function getAllCalledToolNames(result: RunResult): string[] {
   )
 }
 
+/** Build a diagnostic string from RunResult for assertion failure messages */
+function diagnostics(result: RunResult): string {
+  const errorEvents = result.events
+    .filter((e) => e.type === "stopRunByError")
+    .map((e) => {
+      const err = (e as { error?: { name: string; message: string } }).error
+      return err ? `${err.name}: ${err.message}` : "unknown error"
+    })
+  const parts = [`exitCode=${result.exitCode}`]
+  if (result.stderr) parts.push(`stderr=${result.stderr.slice(0, 500)}`)
+  if (errorEvents.length > 0) parts.push(`errors=[${errorEvents.join(", ")}]`)
+  return parts.join("\n")
+}
+
 describe("create-expert", () => {
   it(
     "should create a new perstack.toml",
@@ -77,7 +91,7 @@ describe("create-expert", () => {
         tempDir,
       )
 
-      expect(result.exitCode).toBe(0)
+      expect(result.exitCode, diagnostics(result)).toBe(0)
 
       // Verify control flow: coordinator starts, delegates, then completes
       const controlFlow = result.events
@@ -143,7 +157,7 @@ pick = ["attemptCompletion"]
 
       const result = await runCreateExpert("Add a testing expert that runs unit tests", tempDir)
 
-      expect(result.exitCode).toBe(0)
+      expect(result.exitCode, diagnostics(result)).toBe(0)
 
       // Verify control flow: start → delegate → complete
       expect(