Simplify session lifecycle and MCP cleanup

internal/mcp/protocol_test.go

@@ -126,3 +126,19 @@ func TestPingReturnsEmptyObject(t *testing.T) {
 		t.Fatal("ping result missing")
 	}
 }
+
+func TestTypedInvalidArgsMapToInvalidParams(t *testing.T) {
+	for _, errKind := range []string{ErrorKindInvalidArgs, ErrorKindInvalidKind} {
+		_, code, msg, data := mapToolError(Errorf(errKind, "bad args"))
+		if code != codeInvalidParams {
+			t.Fatalf("%s code = %d, want %d", errKind, code, codeInvalidParams)
+		}
+		if msg != "bad args" {
+			t.Fatalf("%s message = %q", errKind, msg)
+		}
+		kind, ok := data.(map[string]string)
+		if !ok || kind["kind"] != errKind {
+			t.Fatalf("%s data = %#v", errKind, data)
+		}
+	}
+}