[Feature]: Cross-provider delegated agents

[doubletwisted]

Before submitting

• I searched existing issues and Ideas discussions.
• This describes a concrete use case.

Area

Provider orchestration and Agents panel.

Problem or use case

A parent agent cannot delegate work to a different provider through T3.

For example, a Codex parent should be able to start an OpenCode worker, monitor it, receive its result, send follow-ups, and stop it. Today, T3 only sees the worker as a terminal process.

Proposed solution

Add a provider-neutral interface such as:

• agent.spawn
• agent.send
• agent.wait
• agent.stop

T3 would track the parent-child relationship and display the worker in the existing Agents panel.

Why this matters

Different providers and models suit different jobs. This would let one capable model coordinate cheaper or specialized workers without losing visibility in T3.

Smallest useful scope

Support OpenCode workers launched by another provider, using the user's existing CLI authentication.

Alternatives considered

Running opencode run manually works, but T3 cannot track or control the resulting agent.

Risks or tradeoffs

Session recovery, cancellation, and provider-specific behavior need clear handling.

Examples or references

Related: #5479, #2921, #5699, and #7393.

Contribution

• I would be open to helping implement this.