fix(copilot): surface error cause chain in sim-to-go span status (#5473)

markSpanForError only recorded the top-level exception message, so a
fetch() failure showed up as the generic "TypeError: fetch failed" with
no indication of the real cause (ENOTFOUND, ECONNREFUSED, etc). Use
describeError to walk the cause chain and set it as the span status
message and an error.code attribute.

Author: waleedlatif1

apps/sim/lib/copilot/request/otel.ts

@@ -10,7 +10,7 @@ import {
   TraceFlags,
   trace,
 } from '@opentelemetry/api'
-import { toError } from '@sim/utils/errors'
+import { describeError, toError } from '@sim/utils/errors'
 import { RequestTraceV1Outcome } from '@/lib/copilot/generated/request-trace-v1'
 import {
   CopilotBranchKind,
@@ -95,10 +95,14 @@ export function isActionableErrorStatus(code: number): boolean {
 export function markSpanForError(span: Span, error: unknown): void {
   const asError = toError(error)
   span.recordException(asError)
+  const described = describeError(error)
+  if (described.code) {
+    span.setAttribute(TraceAttr.ErrorCode, described.code)
+  }
   if (!isExplicitUserStopError(error)) {
     span.setStatus({
       code: SpanStatusCode.ERROR,
-      message: asError.message,
+      message: described.causeChain ? described.causeChain.join(' <- ') : asError.message,
     })
   }
 }