[codex] Preserve relay trace error causes (#3377)

Co-authored-by: codex <codex@users.noreply.github.com>

Author: juliusmarminge

packages/shared/src/relayTracing.test.ts

@@ -1,9 +1,16 @@
 import { describe, expect, it } from "@effect/vitest";
 import * as Effect from "effect/Effect";
+import * as Layer from "effect/Layer";
 import * as Option from "effect/Option";
 import * as Tracer from "effect/Tracer";
+import { FetchHttpClient } from "effect/unstable/http";
+import { vi } from "vite-plus/test";
 
-import { RelayClientTracer, withRelayClientTracing } from "./relayTracing.ts";
+import {
+  makeRelayClientTracingLayer,
+  RelayClientTracer,
+  withRelayClientTracing,
+} from "./relayTracing.ts";
 
 function collectingTracer(spans: Array<string>): Tracer.Tracer {
   return Tracer.make({
@@ -54,4 +61,44 @@ describe("withRelayClientTracing", () => {
       expect(userSpans).toEqual(["relay.operation"]);
     }),
   );
+
+  it.effect("preserves nested error causes in exported relay spans", () => {
+    const fetchFn = vi.fn<typeof fetch>(async () => new Response(null, { status: 202 }));
+    const httpClientLayer = FetchHttpClient.layer.pipe(
+      Layer.provide(Layer.succeed(FetchHttpClient.Fetch, fetchFn)),
+    );
+    const tracingLayer = makeRelayClientTracingLayer(
+      {
+        tracesUrl: "https://api.axiom.test/v1/traces",
+        tracesDataset: "relay-traces",
+        tracesToken: "public-ingest-token",
+      },
+      {
+        serviceName: "relay-test",
+        runtime: "test",
+        client: "test",
+      },
+    ).pipe(Layer.provide(httpClientLayer));
+    const rootCause = new Error("relay socket closed");
+    const failure = new Error("relay request failed", { cause: rootCause });
+    const tracedApplication = Layer.effectDiscard(
+      Effect.fail(failure).pipe(
+        Effect.withSpan("relay.failed-operation"),
+        withRelayClientTracing,
+        Effect.exit,
+      ),
+    ).pipe(Layer.provide(tracingLayer));
+
+    return Layer.build(tracedApplication).pipe(
+      Effect.scoped,
+      Effect.andThen(
+        Effect.sync(() => {
+          expect(fetchFn).toHaveBeenCalledOnce();
+          const payload = new TextDecoder().decode(fetchFn.mock.calls[0]?.[1]?.body as Uint8Array);
+          expect(payload).toContain("relay request failed");
+          expect(payload).toContain("relay socket closed");
+        }),
+      ),
+    );
+  });
 });

packages/shared/src/relayTracing.ts

@@ -41,7 +41,16 @@ export const withRelayClientTracing = <A, E, R>(
     ),
   );
 
-function traceSafeError(value: unknown): Error {
+function cleanTraceStack(error: Error): string {
+  const stack = error.stack ?? `${error.name}: ${error.message}`;
+  const lines = stack.split("\n");
+  const effectFrameIndex = lines.findIndex(
+    (line, index) => index > 0 && /(?:Generator\.next|~effect\/Effect)/.test(line),
+  );
+  return effectFrameIndex < 0 ? stack : lines.slice(0, effectFrameIndex).join("\n");
+}
+
+function traceSafeError(value: unknown, seen = new WeakSet<object>()): Error {
   const message =
     value instanceof Error
       ? value.message
@@ -51,12 +60,19 @@ function traceSafeError(value: unknown): Error {
           typeof value.message === "string"
         ? value.message
         : String(value);
-  const error = new Error(message);
+
+  let cause: Error | undefined;
+  if (typeof value === "object" && value !== null && !seen.has(value)) {
+    seen.add(value);
+    if ("cause" in value && value.cause !== undefined) {
+      cause = traceSafeError(value.cause, seen);
+    }
+  }
+
+  const error = new Error(message, cause ? { cause } : undefined);
   if (value instanceof Error) {
     error.name = value.name;
-    if (value.stack !== undefined) {
-      error.stack = value.stack;
-    }
+    error.stack = cleanTraceStack(value);
   } else if (
     typeof value === "object" &&
     value !== null &&
@@ -65,6 +81,9 @@ function traceSafeError(value: unknown): Error {
   ) {
     error.name = value.name;
   }
+  if (cause) {
+    error.stack = `${error.stack ?? `${error.name}: ${error.message}`}\nCaused by: ${cause.stack ?? `${cause.name}: ${cause.message}`}`;
+  }
   return error;
 }