[FEATURE] Agents view missing respawn action for background agents on third-party providers (Bedrock)

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

Description

When using Claude Code with AWS Bedrock as the provider, the agents view (claude agents) does not expose a way to respawn a background agent. The only workaround is to manually identify the job ID from ~/.claude/jobs/ and run claude respawn <id> from the terminal.

Steps to Reproduce

1. Configure Claude Code to use AWS Bedrock as the model provider
2. Start a background agent (/bg or claude --bg)
3. Wait for the agent to complete or fail
4. Open the agents view (claude agents)
5. Attempt to respawn the agent from the UI

Expected Behavior

The agents view should provide a respawn action (button, keybinding, or menu option) for completed/failed background agents, regardless of the configured provider.

Actual Behavior

No respawn affordance is available in the agents view UI. Users must:

1. Navigate to ~/.claude/jobs/
2. Identify the correct job ID
3. Run claude respawn <id> manually

Workaround

ls ~/.claude/jobs/          # find the job ID
claude respawn <job-id>     # respawn it

Environment

- Claude Code version: latest (as of May 2025)
- Provider: AWS Bedrock (CLAUDE_CODE_USE_BEDROCK=1)
- Platform: Linux

Notes

This may be related to #58284 (agent view previously hard-disabled on third-party providers). After that was resolved, the agents view became accessible but some functionality (like respawn) may still be missing or gated.

### Proposed Solution


Add a respawn action to the agents view for completed/failed background agents. This could be:

1. **Keybinding** — e.g., `r` to respawn the currently selected agent (consistent with other single-key actions in the TUI)
2. **Context menu option** — if the agents view supports a menu on the selected job

The action should call the same logic as `claude respawn <id>` internally, regardless of the configured provider. If there are provider-specific limitations preventing respawn (e.g., missing infrastructure), the UI should show the action as disabled with a tooltip/message explaining why, rather than hiding it entirely.

### Alternative Solutions

_No response_

### Priority

Medium - Would be very helpful

### Feature Category

Interactive mode (TUI)

### Use Case Example

_No response_

### Additional Context

_No response_