feat: implement all P1/P2/P3/P4 improvements from issue backlog

P1 correctness:
- filter test files by default (--include-tests to opt in)
- per-module diagrams show cross-module dependency arrows
- qualified type names (Module::TypeName) fix false edges from duplicate names

P2 output richness:
- method parameter types and return types in class diagrams (Rust + Python)
- Python pyproject.toml project analyzer (--level project for monorepos)

P3 unique value:
- boundary rules in archlens.toml ([rules] allow/deny, --strict enforcement)

P4 nice to have:
- dependency weight labels on module arrows (--no-weights to disable)
- --watch mode with 500ms debounce
- D2 renderer adapter (--format d2)
- interactive self-contained HTML viewer (--format html)
- git-aware incremental analysis (--since <ref>)

crates/domain/src/aggregates/code_graph.rs

@@ -72,20 +72,11 @@ impl CodeGraph {
     }
 
     pub fn resolve_relationships(self) -> CodeGraph {
-        let mut file_types: HashMap<String, HashSet<String>> = HashMap::new();
-        let mut name_modules: HashMap<&str, HashSet<Option<&str>>> = HashMap::new();
-        let all_type_names: HashSet<&str> = self.elements.iter().map(|e| e.name()).collect();
+        let qualified_names: HashSet<&str> =
+            self.elements.iter().map(|e| e.qualified_name()).collect();
 
-        for element in &self.elements {
-            file_types
-                .entry(element.file_path().as_str().to_string())
-                .or_default()
-                .insert(element.name().to_string());
-            name_modules
-                .entry(element.name())
-                .or_default()
-                .insert(element.module().map(|m| m.as_str()));
-        }
+        // Also keep bare name lookup for import relationships and unqualified fallback
+        let all_bare_names: HashSet<&str> = self.elements.iter().map(|e| e.name()).collect();
 
         let mut resolved = CodeGraph::new();
         for element in &self.elements {
@@ -97,24 +88,11 @@ impl CodeGraph {
                     resolved.add_relationship(rel.clone());
                 }
                 _ => {
-                    if !all_type_names.contains(rel.source())
-                        || !all_type_names.contains(rel.target())
-                    {
-                        continue;
-                    }
-
-                    if let Some(src_file) = rel.source_file() {
-                        let file_key = src_file.as_str().to_string();
-                        if let Some(types_in_file) = file_types.get(&file_key)
-                            && types_in_file.contains(rel.target())
-                        {
-                            resolved.add_relationship(rel.clone());
-                            continue;
-                        }
-                    }
-
-                    let tgt_modules = &name_modules[rel.target()];
-                    if tgt_modules.len() == 1 {
+                    let src_ok = qualified_names.contains(rel.source())
+                        || all_bare_names.contains(rel.source());
+                    let tgt_ok = qualified_names.contains(rel.target())
+                        || all_bare_names.contains(rel.target());
+                    if src_ok && tgt_ok {
                         resolved.add_relationship(rel.clone());
                     }
                 }
@@ -152,6 +130,129 @@ impl CodeGraph {
         filtered
     }
 
+    pub fn qualify(self) -> CodeGraph {
+        // Build lookup: bare name -> Vec<qualified_name> (for disambiguation)
+        let mut name_to_qualified: HashMap<&str, Vec<String>> = HashMap::new();
+        for element in &self.elements {
+            let qn = match element.module() {
+                Some(m) => format!("{}::{}", m.as_str(), element.name()),
+                None => element.name().to_string(),
+            };
+            name_to_qualified
+                .entry(element.name())
+                .or_default()
+                .push(qn);
+        }
+
+        // Build lookup: file_path -> qualified source names in that file
+        let mut file_to_qualified: HashMap<&str, Vec<String>> = HashMap::new();
+        for element in &self.elements {
+            let qn = match element.module() {
+                Some(m) => format!("{}::{}", m.as_str(), element.name()),
+                None => element.name().to_string(),
+            };
+            file_to_qualified
+                .entry(element.file_path().as_str())
+                .or_default()
+                .push(qn);
+        }
+
+        let mut qualified = CodeGraph::new();
+
+        // 1. Qualify element names
+        for element in &self.elements {
+            let qn = match element.module() {
+                Some(m) => format!("{}::{}", m.as_str(), element.name()),
+                None => element.name().to_string(),
+            };
+            qualified.add_element(element.clone().with_qualified_name(qn));
+        }
+
+        // 2. Rewrite relationship source/target
+        for rel in &self.relationships {
+            // Qualify source: find the qualified name of the source in its file
+            let src_qualified = rel
+                .source_file()
+                .and_then(|f| file_to_qualified.get(f.as_str()))
+                .and_then(|qns| {
+                    qns.iter().find(|qn| {
+                        qn.ends_with(&format!("::{}", rel.source())) || *qn == rel.source()
+                    })
+                })
+                .cloned()
+                .unwrap_or_else(|| {
+                    // Fall back: unambiguous lookup
+                    name_to_qualified
+                        .get(rel.source())
+                        .filter(|v| v.len() == 1)
+                        .and_then(|v| v.first())
+                        .cloned()
+                        .unwrap_or_else(|| rel.source().to_string())
+                });
+
+            // Qualify target: prefer same module as source when ambiguous
+            let src_module = src_qualified.split("::").next().unwrap_or("");
+            let tgt_qualified = match name_to_qualified.get(rel.target()) {
+                Some(candidates) if candidates.len() == 1 => candidates[0].clone(),
+                Some(candidates) => {
+                    // Prefer same module as source
+                    candidates
+                        .iter()
+                        .find(|qn| qn.starts_with(&format!("{}::", src_module)))
+                        .cloned()
+                        .unwrap_or_else(|| rel.target().to_string())
+                }
+                None => rel.target().to_string(),
+            };
+
+            let new_rel = Relationship::new(&src_qualified, &tgt_qualified, rel.kind())
+                .unwrap_or_else(|_| rel.clone());
+            let new_rel = if let Some(f) = rel.source_file() {
+                new_rel.with_source_file(f.clone())
+            } else {
+                new_rel
+            };
+            qualified.add_relationship(new_rel);
+        }
+
+        qualified
+    }
+
+    pub fn cross_module_deps_for(&self, module: &ModuleName) -> Vec<(ModuleName, usize)> {
+        let module_element_qnames: HashSet<&str> = self
+            .elements
+            .iter()
+            .filter(|e| e.module().is_some_and(|m| m == module))
+            .map(|e| e.qualified_name())
+            .collect();
+
+        let target_module_of: HashMap<&str, Option<&ModuleName>> = self
+            .elements
+            .iter()
+            .map(|e| (e.qualified_name(), e.module()))
+            .collect();
+
+        let mut counts: HashMap<&str, usize> = HashMap::new();
+        for rel in &self.relationships {
+            if !module_element_qnames.contains(rel.source()) {
+                continue;
+            }
+            if module_element_qnames.contains(rel.target()) {
+                continue;
+            }
+            if let Some(Some(target_mod)) = target_module_of.get(rel.target()) {
+                *counts.entry(target_mod.as_str()).or_insert(0) += 1;
+            }
+        }
+
+        let mut result: Vec<(ModuleName, usize)> = counts
+            .into_iter()
+            .filter_map(|(name, count)| ModuleName::new(name).ok().map(|m| (m, count)))
+            .collect();
+        result.sort_by(|a, b| a.0.as_str().cmp(b.0.as_str()));
+        result
+    }
+
     pub fn subgraph_by_module(&self, module: &ModuleName) -> CodeGraph {
         let filtered_elements: Vec<CodeElement> = self
             .elements
@@ -160,12 +261,15 @@ impl CodeGraph {
             .cloned()
             .collect();
 
-        let element_names: HashSet<&str> = filtered_elements.iter().map(|e| e.name()).collect();
+        let element_qnames: HashSet<&str> = filtered_elements
+            .iter()
+            .map(|e| e.qualified_name())
+            .collect();
 
         let filtered_relationships: Vec<Relationship> = self
             .relationships
             .iter()
-            .filter(|r| element_names.contains(r.source()) && element_names.contains(r.target()))
+            .filter(|r| element_qnames.contains(r.source()) && element_qnames.contains(r.target()))
             .cloned()
             .collect();
 

crates/domain/src/entities/code_element.rs

@@ -3,6 +3,7 @@ use crate::{CodeElementKind, DomainError, FilePath, ModuleName, Visibility};
 #[derive(Debug, Clone)]
 pub struct CodeElement {
     name: String,
+    qualified_name: Option<String>,
     kind: CodeElementKind,
     file_path: FilePath,
     line: usize,
@@ -27,6 +28,7 @@ impl CodeElement {
         }
         Ok(Self {
             name: trimmed.to_string(),
+            qualified_name: None,
             kind,
             file_path,
             line,
@@ -59,10 +61,19 @@ impl CodeElement {
         self
     }
 
+    pub fn with_qualified_name(mut self, qn: String) -> Self {
+        self.qualified_name = Some(qn);
+        self
+    }
+
     pub fn name(&self) -> &str {
         &self.name
     }
 
+    pub fn qualified_name(&self) -> &str {
+        self.qualified_name.as_deref().unwrap_or(&self.name)
+    }
+
     pub fn kind(&self) -> CodeElementKind {
         self.kind
     }

crates/domain/src/lib.rs

@@ -11,4 +11,5 @@ pub use error::DomainError;
 pub use value_objects::analysis::{AnalysisConfig, AnalysisResult, AnalysisWarning};
 pub use value_objects::graph::{CodeElementKind, RelationshipKind, Visibility};
 pub use value_objects::output::{DiagramLevel, OutputConfig, RenderOutput, RenderedFile};
+pub use value_objects::rules::{BoundaryRule, RuleKind, RuleViolation, check_boundary_rules};
 pub use value_objects::source::{FilePath, Language, ModuleName, SourceFile};

crates/domain/src/ports/config_loader.rs

@@ -3,4 +3,8 @@ use crate::{AnalysisConfig, DomainError, OutputConfig};
 pub trait ConfigLoader {
     fn load_analysis_config(&self) -> Result<AnalysisConfig, DomainError>;
     fn load_output_config(&self) -> Result<OutputConfig, DomainError>;
+
+    fn load_rules(&self) -> (Vec<String>, Vec<String>) {
+        (Vec::new(), Vec::new())
+    }
 }

crates/domain/src/ports/diagram_renderer.rs

@@ -1,5 +1,15 @@
-use crate::{CodeGraph, DomainError, RenderOutput};
+use crate::{CodeGraph, DomainError, ModuleName, RenderOutput};
 
 pub trait DiagramRenderer {
     fn render(&self, graph: &CodeGraph) -> Result<RenderOutput, DomainError>;
+
+    fn append_cross_module_deps(
+        &self,
+        content: &str,
+        module: &ModuleName,
+        deps: &[(ModuleName, usize)],
+    ) -> String {
+        let _ = (module, deps);
+        content.to_string()
+    }
 }

crates/domain/src/value_objects/analysis/analysis_config.rs

@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 
 use crate::DiagramLevel;
 
@@ -8,6 +8,8 @@ pub struct AnalysisConfig {
     level: DiagramLevel,
     module_mappings: HashMap<String, String>,
     scope: Option<String>,
+    include_tests: bool,
+    changed_files: Option<HashSet<String>>,
 }
 
 impl AnalysisConfig {
@@ -46,6 +48,24 @@ impl AnalysisConfig {
     pub fn scope(&self) -> Option<&str> {
         self.scope.as_deref()
     }
+
+    pub fn with_include_tests(mut self, include: bool) -> Self {
+        self.include_tests = include;
+        self
+    }
+
+    pub fn include_tests(&self) -> bool {
+        self.include_tests
+    }
+
+    pub fn with_changed_files(mut self, files: HashSet<String>) -> Self {
+        self.changed_files = Some(files);
+        self
+    }
+
+    pub fn changed_files(&self) -> Option<&HashSet<String>> {
+        self.changed_files.as_ref()
+    }
 }
 
 impl Default for AnalysisConfig {
@@ -55,6 +75,8 @@ impl Default for AnalysisConfig {
             level: DiagramLevel::Module,
             module_mappings: HashMap::new(),
             scope: None,
+            include_tests: false,
+            changed_files: None,
         }
     }
 }

crates/domain/src/value_objects/mod.rs

@@ -1,4 +1,5 @@
 pub mod analysis;
 pub mod graph;
 pub mod output;
+pub mod rules;
 pub mod source;

crates/domain/src/value_objects/rules/boundary_rule.rs

@@ -0,0 +1,28 @@
+pub struct BoundaryRule {
+    source: String,
+    target: String,
+}
+
+impl BoundaryRule {
+    pub fn parse(s: &str) -> Option<Self> {
+        let (src, tgt) = s.split_once("-->")?;
+        let source = src.trim().to_string();
+        let target = tgt.trim().to_string();
+        if source.is_empty() || target.is_empty() {
+            return None;
+        }
+        Some(Self { source, target })
+    }
+
+    pub fn source(&self) -> &str {
+        &self.source
+    }
+
+    pub fn target(&self) -> &str {
+        &self.target
+    }
+
+    pub fn matches(&self, src_module: &str, tgt_module: &str) -> bool {
+        self.source == src_module && self.target == tgt_module
+    }
+}

crates/domain/src/value_objects/rules/mod.rs

@@ -0,0 +1,52 @@
+mod boundary_rule;
+mod rule_violation;
+
+pub use boundary_rule::BoundaryRule;
+pub use rule_violation::{RuleKind, RuleViolation};
+
+use std::collections::HashSet;
+
+use crate::{CodeGraph, RelationshipKind};
+
+pub fn check_boundary_rules(
+    graph: &CodeGraph,
+    allow: &[BoundaryRule],
+    deny: &[BoundaryRule],
+) -> Vec<RuleViolation> {
+    if allow.is_empty() && deny.is_empty() {
+        return Vec::new();
+    }
+
+    // Build qualified-name → module lookup
+    let qname_to_module: std::collections::HashMap<&str, &str> = graph
+        .elements()
+        .iter()
+        .filter_map(|e| e.module().map(|m| (e.qualified_name(), m.as_str())))
+        .collect();
+
+    // Collect unique cross-module edges
+    let mut edges: HashSet<(String, String)> = HashSet::new();
+    for rel in graph.relationships() {
+        if rel.kind() == RelationshipKind::Import {
+            continue;
+        }
+        let src_mod = qname_to_module.get(rel.source()).copied();
+        let tgt_mod = qname_to_module.get(rel.target()).copied();
+        if let (Some(s), Some(t)) = (src_mod, tgt_mod)
+            && s != t
+        {
+            edges.insert((s.to_string(), t.to_string()));
+        }
+    }
+
+    let mut violations = Vec::new();
+    for (src, tgt) in &edges {
+        if deny.iter().any(|r| r.matches(src, tgt)) {
+            violations.push(RuleViolation::new(src, tgt, RuleKind::Denied));
+        } else if !allow.is_empty() && !allow.iter().any(|r| r.matches(src, tgt)) {
+            violations.push(RuleViolation::new(src, tgt, RuleKind::NotAllowed));
+        }
+    }
+
+    violations
+}

crates/domain/src/value_objects/rules/rule_violation.rs

@@ -0,0 +1,45 @@
+pub enum RuleKind {
+    Denied,
+    NotAllowed,
+}
+
+pub struct RuleViolation {
+    source_module: String,
+    target_module: String,
+    kind: RuleKind,
+}
+
+impl RuleViolation {
+    pub fn new(source_module: &str, target_module: &str, kind: RuleKind) -> Self {
+        Self {
+            source_module: source_module.to_string(),
+            target_module: target_module.to_string(),
+            kind,
+        }
+    }
+
+    pub fn source_module(&self) -> &str {
+        &self.source_module
+    }
+
+    pub fn target_module(&self) -> &str {
+        &self.target_module
+    }
+
+    pub fn kind(&self) -> &RuleKind {
+        &self.kind
+    }
+
+    pub fn message(&self) -> String {
+        match self.kind {
+            RuleKind::Denied => format!(
+                "Denied dependency: {} --> {}",
+                self.source_module, self.target_module
+            ),
+            RuleKind::NotAllowed => format!(
+                "Dependency not in allow list: {} --> {}",
+                self.source_module, self.target_module
+            ),
+        }
+    }
+}

crates/domain/tests/boundary_rule_tests.rs

@@ -0,0 +1,80 @@
+use archlens_domain::{
+    BoundaryRule, CodeElement, CodeElementKind, CodeGraph, FilePath, ModuleName, Relationship,
+    RelationshipKind, RuleViolation, check_boundary_rules,
+};
+
+fn make_element(name: &str, module: &str) -> CodeElement {
+    CodeElement::new(
+        name,
+        CodeElementKind::Class,
+        FilePath::new(&format!("src/{name}.rs")).unwrap(),
+        1,
+    )
+    .unwrap()
+    .with_module(ModuleName::new(module).unwrap())
+}
+
+fn graph_with_edge(
+    src_name: &str,
+    src_module: &str,
+    tgt_name: &str,
+    tgt_module: &str,
+) -> CodeGraph {
+    let mut graph = CodeGraph::new();
+    graph.add_element(make_element(src_name, src_module));
+    graph.add_element(make_element(tgt_name, tgt_module));
+    graph.add_relationship(
+        Relationship::new(src_name, tgt_name, RelationshipKind::Composition).unwrap(),
+    );
+    graph.qualify()
+}
+
+#[test]
+fn boundary_rule_parses_source_and_target() {
+    let rule = BoundaryRule::parse("Application --> Domain").unwrap();
+    assert_eq!(rule.source(), "Application");
+    assert_eq!(rule.target(), "Domain");
+}
+
+#[test]
+fn check_returns_denied_violation_when_deny_rule_matches_edge() {
+    let graph = graph_with_edge("Service", "Domain", "Adapter", "Adapters");
+
+    let deny = vec![BoundaryRule::parse("Domain --> Adapters").unwrap()];
+    let violations = check_boundary_rules(&graph, &[], &deny);
+
+    assert_eq!(violations.len(), 1);
+    assert_eq!(violations[0].source_module(), "Domain");
+    assert_eq!(violations[0].target_module(), "Adapters");
+    assert!(matches!(
+        violations[0].kind(),
+        archlens_domain::RuleKind::Denied
+    ));
+}
+
+#[test]
+fn check_returns_no_violation_when_edge_matches_allow_rule() {
+    let graph = graph_with_edge("Service", "Application", "Order", "Domain");
+
+    let allow = vec![BoundaryRule::parse("Application --> Domain").unwrap()];
+    let violations = check_boundary_rules(&graph, &allow, &[]);
+
+    assert!(
+        violations.is_empty(),
+        "expected no violations, got: {}",
+        violations.len()
+    );
+}
+
+#[test]
+fn check_returns_not_allowed_when_edge_absent_from_allow_list() {
+    let graph = graph_with_edge("Repo", "Adapters", "Order", "Domain");
+
+    // Only Application --> Domain is allowed; Adapters --> Domain is not in the list
+    let allow = vec![BoundaryRule::parse("Application --> Domain").unwrap()];
+    let violations = check_boundary_rules(&graph, &allow, &[]);
+
+    assert_eq!(violations.len(), 1);
+    assert_eq!(violations[0].source_module(), "Adapters");
+    assert_eq!(violations[0].target_module(), "Domain");
+}

crates/domain/tests/code_graph_tests.rs

@@ -115,6 +115,180 @@ fn subgraph_of_nonexistent_module_is_empty() {
     assert!(subgraph.relationships().is_empty());
 }
 
+#[test]
+fn qualify_sets_qualified_name_on_elements_with_modules() {
+    let mut graph = CodeGraph::new();
+    graph.add_element(make_element("DtoBaseModel", Some("Commons")));
+    graph.add_element(make_element("DtoBaseModel", Some("Api")));
+    graph.add_element(make_element("Orphan", None));
+
+    let graph = graph.qualify();
+
+    let commons_dto = graph
+        .elements()
+        .iter()
+        .find(|e| e.module().map(|m| m.as_str()) == Some("Commons"))
+        .unwrap();
+    assert_eq!(commons_dto.qualified_name(), "Commons::DtoBaseModel");
+
+    let api_dto = graph
+        .elements()
+        .iter()
+        .find(|e| e.module().map(|m| m.as_str()) == Some("Api"))
+        .unwrap();
+    assert_eq!(api_dto.qualified_name(), "Api::DtoBaseModel");
+
+    let orphan = graph
+        .elements()
+        .iter()
+        .find(|e| e.name() == "Orphan")
+        .unwrap();
+    assert_eq!(orphan.qualified_name(), "Orphan");
+}
+
+#[test]
+fn qualify_rewrites_unambiguous_relationship_target() {
+    let mut graph = CodeGraph::new();
+    graph.add_element(make_element("OrderService", Some("App")));
+    graph.add_element(make_element("Order", Some("Domain")));
+    graph.add_relationship(
+        Relationship::new("OrderService", "Order", RelationshipKind::Composition).unwrap(),
+    );
+
+    let graph = graph.qualify();
+
+    let rel = &graph.relationships()[0];
+    assert_eq!(rel.source(), "App::OrderService");
+    assert_eq!(rel.target(), "Domain::Order");
+}
+
+#[test]
+fn qualify_disambiguates_target_by_source_module() {
+    let mut graph = CodeGraph::new();
+    // DtoBaseModel exists in both Commons and Api
+    graph.add_element(make_element("DtoBaseModel", Some("Commons")));
+    graph.add_element(make_element("DtoBaseModel", Some("Api")));
+    // GlobalAudienceDefinition inherits DtoBaseModel, and is in Commons
+    graph.add_element(make_element("GlobalAudienceDefinition", Some("Commons")));
+
+    let mut rel = Relationship::new(
+        "GlobalAudienceDefinition",
+        "DtoBaseModel",
+        RelationshipKind::Inheritance,
+    )
+    .unwrap();
+    // source_file is in the Commons module path
+    rel = rel.with_source_file(
+        archlens_domain::FilePath::new("src/commons/global_audience.rs").unwrap(),
+    );
+    // Make GlobalAudienceDefinition's element file match
+    let mut gad = make_element("GlobalAudienceDefinition", Some("Commons"));
+    // rebuild with matching file_path
+    gad = CodeElement::new(
+        "GlobalAudienceDefinition",
+        archlens_domain::CodeElementKind::Class,
+        archlens_domain::FilePath::new("src/commons/global_audience.rs").unwrap(),
+        1,
+    )
+    .unwrap()
+    .with_module(archlens_domain::ModuleName::new("Commons").unwrap());
+
+    let mut graph = CodeGraph::new();
+    graph.add_element(make_element("DtoBaseModel", Some("Commons")));
+    graph.add_element(make_element("DtoBaseModel", Some("Api")));
+    graph.add_element(gad);
+    graph.add_relationship(rel);
+
+    let graph = graph.qualify();
+
+    let rel = &graph.relationships()[0];
+    assert_eq!(rel.source(), "Commons::GlobalAudienceDefinition");
+    assert_eq!(rel.target(), "Commons::DtoBaseModel");
+}
+
+#[test]
+fn resolve_preserves_relationship_when_both_qualified_names_exist() {
+    let mut graph = CodeGraph::new();
+    graph.add_element(make_element("GlobalAudienceDefinition", Some("Commons")));
+    graph.add_element(make_element("DtoBaseModel", Some("Commons")));
+    graph.add_element(make_element("DtoBaseModel", Some("Api")));
+
+    graph.add_relationship(
+        Relationship::new(
+            "GlobalAudienceDefinition",
+            "DtoBaseModel",
+            RelationshipKind::Inheritance,
+        )
+        .unwrap(),
+    );
+
+    let graph = graph.qualify().resolve_relationships();
+
+    // The relationship should survive — Commons::GlobalAudienceDefinition --> Commons::DtoBaseModel
+    assert_eq!(graph.relationships().len(), 1);
+    assert_eq!(
+        graph.relationships()[0].source(),
+        "Commons::GlobalAudienceDefinition"
+    );
+    assert_eq!(graph.relationships()[0].target(), "Commons::DtoBaseModel");
+}
+
+#[test]
+fn cross_module_deps_for_returns_target_module_with_count() {
+    let mut graph = CodeGraph::new();
+    graph.add_element(make_element("WidgetJobData", Some("aiss_worker")));
+    graph.add_element(make_element("WidgetType", Some("commons")));
+
+    graph.add_relationship(
+        Relationship::new("WidgetJobData", "WidgetType", RelationshipKind::Composition).unwrap(),
+    );
+
+    let module = ModuleName::new("aiss_worker").unwrap();
+    let deps = graph.cross_module_deps_for(&module);
+
+    assert_eq!(deps.len(), 1);
+    assert_eq!(deps[0].0.as_str(), "commons");
+    assert_eq!(deps[0].1, 1);
+}
+
+#[test]
+fn cross_module_deps_for_returns_empty_for_intra_module_only() {
+    let mut graph = CodeGraph::new();
+    graph.add_element(make_element("OrderService", Some("Orders")));
+    graph.add_element(make_element("Order", Some("Orders")));
+    graph.add_relationship(
+        Relationship::new("OrderService", "Order", RelationshipKind::Composition).unwrap(),
+    );
+
+    let module = ModuleName::new("Orders").unwrap();
+    let deps = graph.cross_module_deps_for(&module);
+
+    assert!(deps.is_empty());
+}
+
+#[test]
+fn cross_module_deps_for_aggregates_multiple_relationships_to_same_module() {
+    let mut graph = CodeGraph::new();
+    graph.add_element(make_element("ServiceA", Some("app")));
+    graph.add_element(make_element("ServiceB", Some("app")));
+    graph.add_element(make_element("DomainType1", Some("domain")));
+    graph.add_element(make_element("DomainType2", Some("domain")));
+
+    graph.add_relationship(
+        Relationship::new("ServiceA", "DomainType1", RelationshipKind::Composition).unwrap(),
+    );
+    graph.add_relationship(
+        Relationship::new("ServiceB", "DomainType2", RelationshipKind::Composition).unwrap(),
+    );
+
+    let module = ModuleName::new("app").unwrap();
+    let deps = graph.cross_module_deps_for(&module);
+
+    assert_eq!(deps.len(), 1);
+    assert_eq!(deps[0].0.as_str(), "domain");
+    assert_eq!(deps[0].1, 2);
+}
+
 #[test]
 fn graph_lists_unique_modules() {
     let mut graph = CodeGraph::new();