feat(validate): check parent concept exists for sub_concepts

Added validation that sub_concept declarations reference an existing
parent concept. Produces clear error message with guidance to add
the missing concept declaration.

src/resolve/validate.rs

@@ -410,6 +410,40 @@ pub fn validate_schedule_composition(schedule: &Schedule, collector: &mut ErrorC
     }
 }
 
+/// Validate that all sub_concepts reference existing parent concepts
+pub fn validate_sub_concept_parents(file: &File, collector: &mut ErrorCollector) {
+    // Collect all concept names
+    let concept_names: HashSet<String> = file
+        .declarations
+        .iter()
+        .filter_map(|decl| {
+            if let Declaration::Concept(c) = decl {
+                Some(c.name.clone())
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    // Check each sub_concept references an existing parent
+    for decl in &file.declarations {
+        if let Declaration::SubConcept(sc) = decl {
+            if !concept_names.contains(&sc.parent_concept) {
+                collector.add(ResolveError::ValidationError {
+                    message: format!(
+                        "Parent concept '{}' not found for sub_concept '{}.{}'",
+                        sc.parent_concept, sc.parent_concept, sc.name
+                    ),
+                    help: Some(format!(
+                        "Add 'concept {}' before defining sub_concepts for it.",
+                        sc.parent_concept
+                    )),
+                });
+            }
+        }
+    }
+}
+
 /// Validate an entire file
 ///
 /// Collects all validation errors and returns them together instead of failing
@@ -417,6 +451,9 @@ pub fn validate_schedule_composition(schedule: &Schedule, collector: &mut ErrorC
 pub fn validate_file(file: &File, action_registry: &HashSet<String>) -> Result<()> {
     let mut collector = ErrorCollector::new();
 
+    // Type system validation
+    validate_sub_concept_parents(file, &mut collector);
+
     for decl in &file.declarations {
         match decl {
             | Declaration::Character(c) => {
@@ -652,4 +689,106 @@ mod tests {
         validate_behavior_tree_actions(&tree, &registry, &mut collector);
         assert!(collector.has_errors());
     }
+
+    #[test]
+    fn test_sub_concept_with_valid_parent() {
+        let file = File {
+            declarations: vec![
+                Declaration::Concept(ConceptDecl {
+                    name: "Cup".to_string(),
+                    span: Span::new(0, 10),
+                }),
+                Declaration::SubConcept(SubConceptDecl {
+                    name: "Type".to_string(),
+                    parent_concept: "Cup".to_string(),
+                    kind: SubConceptKind::Enum {
+                        variants: vec![
+                            "Small".to_string(),
+                            "Medium".to_string(),
+                            "Large".to_string(),
+                        ],
+                    },
+                    span: Span::new(20, 60),
+                }),
+            ],
+        };
+
+        let mut collector = ErrorCollector::new();
+        validate_sub_concept_parents(&file, &mut collector);
+        assert!(!collector.has_errors());
+    }
+
+    #[test]
+    fn test_sub_concept_with_missing_parent() {
+        let file = File {
+            declarations: vec![Declaration::SubConcept(SubConceptDecl {
+                name: "Type".to_string(),
+                parent_concept: "Cup".to_string(),
+                kind: SubConceptKind::Enum {
+                    variants: vec!["Small".to_string()],
+                },
+                span: Span::new(0, 40),
+            })],
+        };
+
+        let mut collector = ErrorCollector::new();
+        validate_sub_concept_parents(&file, &mut collector);
+        assert!(collector.has_errors());
+    }
+
+    #[test]
+    fn test_multiple_sub_concepts_same_valid_parent() {
+        let file = File {
+            declarations: vec![
+                Declaration::Concept(ConceptDecl {
+                    name: "Cup".to_string(),
+                    span: Span::new(0, 10),
+                }),
+                Declaration::SubConcept(SubConceptDecl {
+                    name: "Type".to_string(),
+                    parent_concept: "Cup".to_string(),
+                    kind: SubConceptKind::Enum {
+                        variants: vec!["Mug".to_string()],
+                    },
+                    span: Span::new(20, 40),
+                }),
+                Declaration::SubConcept(SubConceptDecl {
+                    name: "Material".to_string(),
+                    parent_concept: "Cup".to_string(),
+                    kind: SubConceptKind::Enum {
+                        variants: vec!["Glass".to_string()],
+                    },
+                    span: Span::new(50, 70),
+                }),
+            ],
+        };
+
+        let mut collector = ErrorCollector::new();
+        validate_sub_concept_parents(&file, &mut collector);
+        assert!(!collector.has_errors());
+    }
+
+    #[test]
+    fn test_sub_concept_wrong_parent_name() {
+        let file = File {
+            declarations: vec![
+                Declaration::Concept(ConceptDecl {
+                    name: "Plate".to_string(),
+                    span: Span::new(0, 10),
+                }),
+                Declaration::SubConcept(SubConceptDecl {
+                    name: "Type".to_string(),
+                    parent_concept: "Cup".to_string(),
+                    kind: SubConceptKind::Enum {
+                        variants: vec!["Small".to_string()],
+                    },
+                    span: Span::new(20, 40),
+                }),
+            ],
+        };
+
+        let mut collector = ErrorCollector::new();
+        validate_sub_concept_parents(&file, &mut collector);
+        assert!(collector.has_errors());
+    }
 }