fix(validate): handle custom types and inherited threads

lib/crates/fabro-validate/src/rules/inert_attribute.rs

@@ -1,4 +1,4 @@
-use fabro_graphviz::graph::Graph;
+use fabro_graphviz::graph::{self, Graph};
 
 use crate::{Diagnostic, LintRule, Severity};
 
@@ -39,6 +39,9 @@ impl LintRule for Rule {
             let Some(handler) = node.handler_type() else {
                 continue;
             };
+            if !graph::is_known_handler_type(handler) {
+                continue;
+            }
             for (attr, consumers) in HANDLER_SPECIFIC_ATTRS {
                 if !node.attrs.contains_key(*attr) {
                     continue;
@@ -217,4 +220,20 @@ mod tests {
         );
         assert!(Rule.apply(&g).is_empty());
     }
+
+    #[test]
+    fn ignores_handler_specific_attrs_on_unrecognized_explicit_types() {
+        let mut g = minimal_graph();
+        let mut node = Node::new("custom");
+        node.attrs.insert(
+            "type".to_string(),
+            AttrValue::String("custom.handler".to_string()),
+        );
+        node.attrs.insert(
+            "script".to_string(),
+            AttrValue::String("echo hi".to_string()),
+        );
+        g.nodes.insert("custom".to_string(), node);
+        assert!(Rule.apply(&g).is_empty());
+    }
 }

lib/crates/fabro-validate/src/rules/parallel_branch_inert_attribute.rs

@@ -11,7 +11,7 @@ pub(super) fn rule() -> Box<dyn LintRule> {
 /// Attributes that parallel branch execution does not resolve. Branch nodes
 /// are dispatched with a snapshot of the context taken when the parallel node
 /// started, so per-branch `fidelity` never changes what a branch sees, and
-/// branches never join conversation threads regardless of `thread_id`.
+/// per-branch `thread_id` never replaces the thread inherited in that snapshot.
 const BRANCH_IGNORED_ATTRS: &[&str] = &["fidelity", "thread_id"];
 
 struct Rule;
@@ -39,7 +39,10 @@ fn fix_message(attr: &str, parallel_ids: &[String]) -> String {
                 )
             }
         }
-        _ => format!("Remove '{attr}': parallel branches never join conversation threads"),
+        "thread_id" => format!(
+            "Remove '{attr}': parallel branches inherit the thread resolved when the parallel node started"
+        ),
+        _ => format!("Remove '{attr}'"),
     }
 }
 
@@ -210,6 +213,12 @@ mod tests {
             Some(("fork".to_string(), "branch_a".to_string()))
         );
         assert!(d[0].message.contains("'thread_id'"));
+        assert_eq!(
+            d[0].fix.as_deref(),
+            Some(
+                "Remove 'thread_id': parallel branches inherit the thread resolved when the parallel node started"
+            )
+        );
     }
 
     #[test]