bxcore, brokerd, loopd: an invalid-arguments denial says why

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/loopd/tests/tools.rs

@@ -5,7 +5,8 @@ mod support;
 
 use bxcore::{CallId, DenyReason, SessionId, ToolRequest, ToolResponse};
 use loopd::tools::{
-    Dispatch, FakeTools, Pending, Registry, ToolPort, cap_result, denial_text, dispatch,
+    Dispatch, FakeTools, Pending, Registry, ToolPort, cap_result, denial_message, denial_text,
+    dispatch,
 };
 
 fn req(tool: &str, arguments: &str) -> ToolRequest {
@@ -252,9 +253,35 @@ fn every_deny_reason_has_its_sentence() {
     ];
     for (reason, want) in table {
         assert_eq!(denial_text(reason), want, "{reason:?}");
+        assert_eq!(
+            denial_message(reason, None),
+            want,
+            "{reason:?}: without a detail, the sentence alone"
+        );
     }
 }
 
+/// The broker's detail goes after the sentence, before its full stop.
+#[test]
+fn a_denial_with_a_detail_appends_it_to_the_sentence() {
+    assert_eq!(
+        denial_message(
+            DenyReason::InvalidArguments,
+            Some("invalid argument shape: unknown field `file`, expected `text`")
+        ),
+        "Denied: the arguments are not valid for this tool: invalid argument shape: unknown field `file`, expected `text`."
+    );
+    assert_eq!(
+        denial_message(DenyReason::InvalidArguments, Some("invalid path: n/a")),
+        "Denied: the arguments are not valid for this tool: invalid path: n/a."
+    );
+    assert_eq!(
+        denial_message(DenyReason::NoGrant, Some("x")),
+        "Denied: no grant allows this call: x.",
+        "any reason's detail is shown the same way"
+    );
+}
+
 #[test]
 fn results_are_cut_on_a_character_boundary_and_marked() {
     assert_eq!(cap_result("short", 100), ("short".to_string(), false));
@@ -296,7 +323,8 @@ fn fake_tools_answer_echo_deny_the_rest_and_record_calls() {
         assert_eq!(
             fake.call(&req(tool, "{}"), &mut on_pending),
             ToolResponse::Denied {
-                reason: DenyReason::NoGrant
+                reason: DenyReason::NoGrant,
+                detail: None,
             },
             "{tool}: the clock is loopd's own now, not the port's"
         );