fix(rig-acp): rig acp refuses an option after acp instead of ignoring it

plugins/rig-acp/src/router.rs

@@ -769,6 +769,16 @@ struct Served {
 /// Makes this app the router: serves the client from the first frame and
 /// exits when the client closes the connection or the app is asked to.
 pub(crate) fn install(app: &mut App) {
+    // A word after `acp`, such as an option, is no option of the run.
+    let invoked = app.world().get_resource::<Invoked>();
+    let after = invoked.map(|invoked| invoked.args.arguments.join(" "));
+    if let Some(after) = after.filter(|after| !after.is_empty()) {
+        app.refuse_run(format!(
+            "rig acp takes nothing after `acp`, so `{after}` would be ignored; put options \
+             before `acp`, as in `rig --{TOOLS}=read acp`"
+        ));
+        return;
+    }
     let world = app.world();
     let (Some(home), Some(stores), Some(runtime), Some(wake)) = (
         world.get_resource::<RigHome>(),
@@ -798,7 +808,7 @@ pub(crate) fn install(app: &mut App) {
             }
         },
     };
-    // Each session checks the tools `rig acp --tools` gives against its own,
+    // Each session checks the tools `rig --tools … acp` gives against its own,
     // the client's MCP servers' among them.
     let invoked = app.world().get_resource::<Invoked>();
     if let Some(tools) = invoked.filter(|invoked| invoked.flag(TOOLS)) {

plugins/rig-acp/src/tests.rs

@@ -893,3 +893,28 @@ fn sleeping(place: &Place) -> bool {
             .is_ok_and(|line| String::from_utf8_lossy(&line).contains("sleep"))
     })
 }
+
+/// `rig acp --tools=read` is refused, saying to put options before `acp`:
+/// the router reads only the options before it, so one after it would be
+/// dropped.
+#[test]
+fn an_option_after_acp_is_refused() {
+    let args = Invocation::parse(&["acp", "--tools=read"]).unwrap_or_default();
+    assert_eq!(args.arguments, ["--tools=read"]);
+    let mut app = App::new();
+    app.insert_resource(Invoked {
+        args,
+        terminal: false,
+    });
+    crate::router::install(&mut app);
+    let refused = app
+        .world()
+        .get_resource::<rig_harness::host::launcher::Refused>();
+    let why = refused
+        .map(|refused| refused.0.as_str())
+        .unwrap_or_default();
+    assert!(
+        why.contains("`--tools=read`") && why.contains("before `acp`"),
+        "{why}"
+    );
+}

plugins/rig-acp/src/tests/flows.rs

@@ -837,7 +837,7 @@ fn a_refused_model_change_says_why_and_keeps_the_model() {
     assert!(router.is_some());
 }
 
-/// `rig acp --tools` reaches each session, which checks it against its own
+/// `rig --tools … acp` reaches each session, which checks it against its own
 /// tools: a name none has refuses the session as it opens, and a known
 /// list keeps the session to it.
 #[test]