init: archlens — architecture diagram generator

Hex arch + DDD, tree-sitter parsing, Mermaid/ASCII output.
Supports Rust + Python. 92 tests. CI, diff, --check for staleness detection.

crates/domain/src/aggregates/code_graph.rs

@@ -0,0 +1,78 @@
+use std::collections::HashSet;
+
+use crate::{CodeElement, ModuleName, Relationship};
+
+#[derive(Debug, Clone)]
+pub struct CodeGraph {
+    elements: Vec<CodeElement>,
+    relationships: Vec<Relationship>,
+}
+
+impl Default for CodeGraph {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl CodeGraph {
+    pub fn new() -> Self {
+        Self {
+            elements: Vec::new(),
+            relationships: Vec::new(),
+        }
+    }
+
+    pub fn add_element(&mut self, element: CodeElement) {
+        self.elements.push(element);
+    }
+
+    pub fn add_relationship(&mut self, relationship: Relationship) {
+        self.relationships.push(relationship);
+    }
+
+    pub fn elements(&self) -> &[CodeElement] {
+        &self.elements
+    }
+
+    pub fn relationships(&self) -> &[Relationship] {
+        &self.relationships
+    }
+
+    pub fn modules(&self) -> Vec<ModuleName> {
+        let mut seen = HashSet::new();
+        let mut modules = Vec::new();
+
+        for element in &self.elements {
+            if let Some(module) = element.module()
+                && seen.insert(module.as_str().to_string())
+            {
+                modules.push(module.clone());
+            }
+        }
+
+        modules
+    }
+
+    pub fn subgraph_by_module(&self, module: &ModuleName) -> CodeGraph {
+        let filtered_elements: Vec<CodeElement> = self
+            .elements
+            .iter()
+            .filter(|e| e.module().is_some_and(|m| m == module))
+            .cloned()
+            .collect();
+
+        let element_names: HashSet<&str> = filtered_elements.iter().map(|e| e.name()).collect();
+
+        let filtered_relationships: Vec<Relationship> = self
+            .relationships
+            .iter()
+            .filter(|r| element_names.contains(r.source()) && element_names.contains(r.target()))
+            .cloned()
+            .collect();
+
+        CodeGraph {
+            elements: filtered_elements,
+            relationships: filtered_relationships,
+        }
+    }
+}