Adapters, plugins and shutdown

An adapter is a service with optional KickJS hooks — beforeMount, onRouteMount, beforeStart, afterStart, onError, onResponse, onHealthCheck, shutdown — plus depends_on, phased middleware, contributors and settings:

pub fn MailAdapter(comptime name: []const u8, comptime Settings: type) type {
    return struct {
        pub const settings = &.{Settings}; // read and validated because this adapter is mounted
        mail: *const Settings,
        process: *const kzig.Process,

        /// Part of /health/ready: 503 "degraded" when any check is down.
        pub fn onHealthCheck(self: *@This()) kzig.HealthCheck {
            return .{ .name = "MailAdapter:" ++ name, .status = if (self.reachable()) .up else .down };
        }
        …
    };
}

$ curl -i localhost:3000/health/ready
HTTP/1.1 503 Service Unavailable
{"status":"degraded","checks":[{"name":"MailAdapter:transactional","status":"down"},{"name":"MailAdapter:marketing","status":"down"}]}

kzig.Plugin(.{ .modules, .adapters, .middleware, .contributors, .settings }) bundles them. On SIGINT/SIGTERM serve stops accepting new connections, requests in flight finish (their sockets are cut after shutdown_timeout_ms, 30 s; a handler still running a second later makes the process exit with status 1 rather than free services under it) and idle connections close; then app.deinit() runs adapters' shutdown in reverse dependency order. /health/* answer draining from the moment shutdown begins, to requests already in flight. /health/ready runs every adapter's check at once, counts one slower than 2 s as down, and shares a run between probes within a second. A contributor's dispose(self, *V) runs when its handler returns, before the response is written — a response body must not borrow memory dispose frees.