[FEATURE] When `apiKeyHelper` fails, it's stderr output should be shown to user in Claude Code

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Users are unable to figure out why the apiKeyHelper failed because all they see is this message, even if the helper emits other messages to stderr:

Error getting API key from apiKeyHelper (in settings or ~/.claude.json): apiKeyHelper did not return a valid value

Proposed Solution

Whatever output the helper sends to stderr (or other mechanism) should be captured by claude and displayed inside claude code.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

Configuration and settings

Use Case Example

Enterprise deployed helper requires user to be on VPN and fails if it's not working, can emit a message to stderr with that problem, which would remind the user to log on.

Helper requires user to first log into their password manager, etc.

Additional Context

_No response_