## Why
An environment connection can be available before its owner has supplied the
configuration for a particular thread attachment. Threads need to start without
blocking while ensuring turns do not use that attachment prematurely.
## What changed
- Accept `Pending` environment configuration and resolve each attachment only
after both its shared executor connection and owner configuration are ready.
- Add a `Failed` configuration state and `environment_failed` callback so an
owner can fail one thread's attachment without affecting other threads.
- Keep pending and failed attachments out of capability-root inspection and turn
environments, and allow failed attachments to recover through a ready update.
- Apply owner configuration before waking a waiting turn so its permission
profile, login-shell policy, capability roots, and tools are immediately
consistent.
## Testing
Add an integration test covering non-blocking thread startup, independent ready
and failed callbacks, waiting-turn resumption, installed capability and tool
configuration, and recovery from failure.
GitOrigin-RevId: d587e2025d584c867d782d470b18bf5a1a27b76c
2ca575026c