fix(subagent): project-agent mcpServers follow folder trust; agent names are one path component

A project-scoped agent definition from an untrusted repository could
declare inline stdio mcpServers and the child session started that
command, while inline hooks on the same definition were already gated on
folder trust. The mcpServers list now uses the same gate.

By-name agent lookup joined the requested name onto each searched
directory, so a name carrying a separator or ".." resolved a file outside
that directory under its trust scope; both lookup entry points now reject
any name that is not a single path component.

Ported from upstream (grok-build subagent/handle_request.rs mcpServers
gate), extended with the name guard.

Claude-Session: https://claude.ai/code/session_01RUqV8HVGXcAETyYbZ2tPQ4

crates/codegen/kigi-agent/src/discovery.rs

@@ -252,11 +252,20 @@ pub fn by_name(name: &str) -> Option<AgentDefinition> {
     by_name_with_home(name, dirs::home_dir().as_deref(), kigi.as_deref())
 }
 
+/// An agent name is one file stem: a separator or `..` would resolve a file outside the searched directory with that directory's trust scope.
+fn is_single_path_component(name: &str) -> bool {
+    !name.is_empty() && name != "." && name != ".." && !name.contains(['/', '\\'])
+}
+
 fn by_name_with_home(
     name: &str,
     home: Option<&Path>,
     kigi_home: Option<&Path>,
 ) -> Option<AgentDefinition> {
+    if !is_single_path_component(name) {
+        tracing::warn!(name, "rejected agent name: not a single path component");
+        return None;
+    }
     // Check built-ins first — type-safe via BuiltinAgentName strum enum.
     // Legacy pre-rebrand agent types (persisted in old session files) are
     // mapped onto their current names first; see `canonical_agent_type`.
@@ -298,6 +307,10 @@ fn by_name_in_cwd_with_home(
     home: Option<&Path>,
     kigi_home: Option<&Path>,
 ) -> Option<AgentDefinition> {
+    if !is_single_path_component(name) {
+        tracing::warn!(name, "rejected agent name: not a single path component");
+        return None;
+    }
     if let Some(def) = load_project_definition_by_name(name, cwd) {
         return Some(def);
     }
@@ -827,6 +840,30 @@ mod tests {
         assert!(def.is_none());
     }
 
+    /// `../outside` must not load a file beyond the agents directory under that directory's scope.
+    #[test]
+    fn by_name_rejects_names_that_leave_the_agents_directory() {
+        let tmp = tempfile::tempdir().unwrap();
+        let project = tmp.path().join("project");
+        let agents_dir = project.join(".kigi").join("agents");
+        fs::create_dir_all(&agents_dir).unwrap();
+        write_agent_file(
+            &project,
+            "outside.md",
+            "outside",
+            "Lives outside the agents dir",
+        );
+        write_agent_file(&agents_dir, "inside.md", "inside", "Lives inside");
+        assert!(by_name_in_cwd_with_home("../../outside", &project, None, None).is_none());
+        assert!(by_name_in_cwd_with_home("..", &project, None, None).is_none());
+        assert!(by_name_in_cwd_with_home("a/b", &project, None, None).is_none());
+        assert!(by_name_with_home("../../outside", None, None).is_none());
+        assert_eq!(
+            by_name_in_cwd_with_home("inside", &project, None, None).map(|d| d.name),
+            Some("inside".to_string())
+        );
+    }
+
     #[test]
     fn test_discover_finds_md_files() {
         let tmp = tempfile::tempdir().unwrap();

crates/codegen/kigi-shell/src/agent/subagent/handle_request.rs

@@ -988,13 +988,22 @@ pub(crate) async fn handle_subagent_request(
             }
         }
     }
-    let agent_mcp_servers: Vec<_> = if is_plugin_agent {
-        if !definition.mcp_servers.is_empty() {
-            tracing::warn!(
-                agent = % definition.name, plugin = ? definition.plugin_name,
-                "ignoring mcpServers on plugin agent (not supported for security)"
-            );
-        }
+    let agent_mcp_servers: Vec<_> = if definition.mcp_servers.is_empty() {
+        vec![]
+    } else if is_plugin_agent {
+        tracing::warn!(
+            agent = % definition.name, plugin = ? definition.plugin_name,
+            "ignoring mcpServers on plugin agent (not supported for security)"
+        );
+        vec![]
+    } else if !crate::agent::folder_trust::agent_inline_hooks_allowed(definition.scope, || {
+        crate::agent::folder_trust::project_scope_allowed(&ctx.parent_cwd)
+    }) {
+        // An untrusted repo's inline stdio MCP command would run like an inline hook.
+        tracing::warn!(
+            agent = % definition.name,
+            "ignoring mcpServers on untrusted project agent (folder not trusted; re-run with --trust)"
+        );
         vec![]
     } else {
         definition