# facet_agent The agent serving surface for facet apps: `enable()` before `app.run`, and a connected agent can read the UI and act through it. ```toml [dependencies] facet_agent = "*" facet_runtime = "*" # plus the agent stack it serves (agent_core/mcp/inapp + the platform # overlay) — `cpc pm add . facet_agent` writes the closure ``` ```cplus import "facet_agent/agent" as agent; import "facet_runtime/runtime" as runtime; fn run() -> i32 { agent::enable(); // register the serving hooks runtime::agent_mcp("myapp"); // serve under this NAME, before startup let app = runtime::App::new("myapp"); app.window("main", Home::boxed); let _run = app.run("main"); return 0 as i32; } ``` An **id, not an address**: the platform derives where it listens from the id and this process's pid. macOS and Linux expose a 0600 Unix socket plus an HTTP port; Windows, iOS, and Android expose the loopback HTTP port. A launcher that spawned the app knows the pid, so it can work the address out without being told. The app also prints it and writes it to `/tmp/mcp--.json`. Without an application policy, a connection receives `operator()` plus `cap_edit_tree()`: it can read and drive ordinary nodes and use the inspector extension, but still cannot cross Protected or Private tiers. Install a `fn(auth::Request) -> auth::Grant` with `set_policy` before `enable()` when the surface must be narrower. `facet_agent/consent` is a ready-made policy that asks the user once per client. `import "facet_agent/agent"` resolves by platform override: AppKit on macOS, GTK on Linux, Win32 on Windows, UIKit on iOS, and the Android agent backend on Android. It installs into Facet's application seam (`application::install_agent`) — facet itself knows nothing about the agent stack. This is facet's OPTIONAL tier as a package boundary (2026-08-17): an app that never imports facet_agent links none of the agent machinery, by construction rather than by promise. | Need | File | |---|---| | Use it in minutes | [docs/tutorial.md](https://github.com/netdur/cplus/blob/v0.0.28/vendor/facet_agent/docs/tutorial.md) | | Why it is shaped this way, and the traps | [docs/guide.md](https://github.com/netdur/cplus/blob/v0.0.28/vendor/facet_agent/docs/guide.md) | | Exact signatures | [docs/ref.md](https://github.com/netdur/cplus/blob/v0.0.28/vendor/facet_agent/docs/ref.md) | Tests: `cd vendor/facet_agent && cpc test`. The suite compiles the serving surface on the active platform — the `vocab::Agent` → policy translation is live code no other build type-checks, and a wrong arm there is a card number readable by every agent that connects.