[FEATURE]: Show provider connection error when running subagents

[Kangaroux]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

When my primary agent loses connection to the provider it displays an error saying it's reconnecting. However, if a subagent is running and connection is lost there is no display. It eventually reconnects, but until then, it can appear that the subagent is stuck

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: UI should indicate when streaming connection is lost/interrupted #15393: [FEATURE]: UI should indicate when streaming connection is lost/interrupted — requests similar UI feedback when a streaming connection stalls, and explicitly mentions that the indicator should apply more broadly (not just the main agent)

You may also want to review #13841 which covers subagent hangs and mentions TUI stall indicators as part of the fix direction.