idle: afk command, configurable session timeout, fix block_reason

Add `poc-daemon afk` to immediately mark Kent as away, allowing the
idle timer to fire without waiting for the session active timeout.

Add `poc-daemon session-timeout <secs>` to configure how long after
the last message Kent counts as "present" (default 15min, persisted).

Fix block_reason() to report "kent present" and "in turn" states
that were checked in the tick but not in the diagnostic output.

src/bin/poc-daemon/rpc.rs

@@ -126,6 +126,25 @@ impl daemon::Server for DaemonImpl {
         Promise::ok(())
     }
 
+    fn afk(
+        &mut self,
+        _params: daemon::AfkParams,
+        _results: daemon::AfkResults,
+    ) -> Promise<(), capnp::Error> {
+        self.state.borrow_mut().handle_afk();
+        Promise::ok(())
+    }
+
+    fn session_timeout(
+        &mut self,
+        params: daemon::SessionTimeoutParams,
+        _results: daemon::SessionTimeoutResults,
+    ) -> Promise<(), capnp::Error> {
+        let secs = pry!(params.get()).get_seconds();
+        self.state.borrow_mut().handle_session_timeout(secs);
+        Promise::ok(())
+    }
+
     fn idle_timeout(
         &mut self,
         params: daemon::IdleTimeoutParams,