[Feature]: Support Prime Agent as a provider (long-running RLM agent via its RPC mode) #6126

Summary

Add a built-in driver + adapter for Prime Agent (https://github.com/PrimeIntellect-ai/prime-agent) so it can be controlled from T3 Code like the existing five providers. Prime Agent is an open-source, self-improving RLM (Recursive Language Model) agent for long-running coding and research tasks — daemon-backed background sessions that survive terminal detach, re-attachable, with persistent goals, heartbeats, schedules, and bounded autonomous mode. That is a capability gap none of the current providers fill, and T3 Code is the natural control surface for it.

Why it fits T3 Code

• T3 Code is provider-agnostic by design. Per docs/internals/providers.md, adding an agent is one Driver + Adapter entry in BUILT_IN_DRIVERS — no orchestration, contract, or client change required.
• Prime Agent ships a headless RPC mode (packages/coding-agent/docs/rpc.md) explicitly for "headless automation and integrations" — the ready-made transport for an adapter.
• Complementary overlap: T3 Code gives the human surface (threads, diffs, approval, phone remote); Prime Agent gives long-running autonomous research (persistent IPython runtime, programmatic subagents via rlm(...), /refine self-improvement, /autonomous budgets).

What it would take

• New driverKind primeAgent + adapter mapping Prime Agent's RPC/JSON streams onto ProviderAdapter.
• Config schema mirroring existing drivers. Auth is flexible: subscriptions (Claude / Codex / GitHub Copilot OAuth) or API keys (OpenAI, Anthropic, DeepSeek, OpenRouter, …) via ~/.prime/agent/auth.json.
• Notes: Prime Agent is daemon/TUI-first rather than a plain stdio CLI, so the adapter would talk to its RPC surface instead of an app-server like Codex. macOS/Linux only today; MIT licensed.

Considerations

• CONTRIBUTING notes large feature work is least likely to be accepted — this is a request for maintainers to consider, not a demand. Happy to test an RPC-mode integration or provide a minimal proof-of-concept adapter if that helps de-risk it.
• Possible long-term seam worth weighing: Grok already speaks ACP; a generic ACP-based driver could cover Prime Agent and future agents in one move, instead of per-agent custom adapters.

Environment

• T3 Code nightly 0.0.33, macOS