[rayapp] updating rayapp to handle errors correctly

[elliot-barn]

Problem

The anyscale CLI sometimes exits with code 0 even when a remote run_command
has failed. In those cases it logs the failure via logrus to stderr, e.g.:

time="2026-05-04T19:45:34Z" level=fatal msg="exec failed with exit code 1"

Previously, runAnyscaleCLI in rayapp/anyscale_cli.go only scanned stdout
for the exec failed with exit code marker when the exit code was 0, so these
failures were silently treated as success. (Non-zero exits were already handled
and did include stderr in the error message — the gap was specifically the
exit-0-with-stderr-marker case.)

Changes

rayapp/anyscale_cli.go

• Capture stderr into a local variable unconditionally (alongside stdout)
  after cmd.Run().
• Extend the post-success check to scan both stdout and stderr for
  "exec failed with exit code".
• When that marker is found, include both streams in the returned error
  for full diagnostic context.

rayapp/anyscale_cli_test.go

• Rename the existing stdout-marker case to "exec failed with exit code in stdout".
• Add a new case "exec failed with exit code in stderr" that simulates the
  logrus-style stderr output (level=fatal msg="exec failed with exit code 1")
  with exit code 0, and asserts the error is still surfaced.

Uncaught failure: https://buildkite.com/anyscale/template-probe/builds/42/canvas?jid=019e1cb4-1046-4ee7-a113-790ea651edbf&tab=output#019e1cb4-1046-4ee7-a113-790ea651edbf/L712

[gemini-code-assist]

Code Review

This pull request updates the Anyscale CLI wrapper to correctly detect remote command failures that log 'exec failed with exit code' to stderr while exiting with a zero status code. It ensures both stdout and stderr are captured and included in the error message. Additionally, a new test case was added to verify this behavior for stderr. The reviewer suggested using a constant for the failure message string to improve maintainability and making the error message more descriptive.

[gemini-code-assist]

The error message "command failed:" is somewhat generic. Since this block specifically handles a known CLI issue where it exits with 0 despite a remote failure, using a constant for the error string and including it in the error message improves both maintainability and error clarity for the user.

Suggested change

	if strings.Contains(stdout, "exec failed with exit code") ||
	strings.Contains(stderr, "exec failed with exit code") {
	return "", fmt.Errorf(
	"anyscale error: command failed:\nstdout: %s\nstderr: %s",
	stdout, stderr,
	)
	}
	const failureMsg = "exec failed with exit code"
	if strings.Contains(stdout, failureMsg) ||
	strings.Contains(stderr, failureMsg) {
	return "", fmt.Errorf(
	"anyscale error: %s detected:\nstdout: %s\nstderr: %s",
	failureMsg, stdout, stderr,
	)
	}