car-external-agents

Detection of installed agentic CLIs — Claude Code, Codex, Gemini — so CAR can treat them as agents the user can dispatch tasks to, sharing their existing subscription auth instead of forcing the user to register an API key.

This crate is the discovery side of the third kind of agent in CAR's taxonomy, sibling to car-registry::supervisor (lifecycle agents) and car_multi::AgentRunner (in-process runners). External agents are caller-installed CLIs spawned per task — the daemon discovers them but does not own their lifecycle.

See docs/proposals/external-agent-detection.md for the architectural rationale and phasing.

Phase 1 (this crate today)

• detect() — scan $PATH for known adapter binaries, probe version + auth state, return a stable ExternalAgentSpec list.
• Per-tool adapters are static descriptors (binary name, capabilities, auth heuristic). Adding a fourth adapter is a ~50-line file under src/adapters/.

Phase 2 (next) adds the per-task adapter that speaks each tool's JSON stdio protocol natively in Rust, exposed as agents.invoke_external.

What this is not

• Not a model provider — the SDKs are agents (own planning loop, tool use, sessions), not generate() calls. Modeling them as ProtocolHandler would be the wrong abstraction.
• Not a lifecycle supervisor — external agents are spawned per task, not kept running. car-registry::supervisor handles long-lived services.
• Not a credential reader — auth-kind probing inspects credential file shape only. We never read credential values.