diff --git a/crates/prometeu-compiler/src/frontends/pbs/collector.rs b/crates/prometeu-compiler/src/frontends/pbs/collector.rs
new file mode 100644
index 00000000..2a5c36ea
--- /dev/null
+++ b/crates/prometeu-compiler/src/frontends/pbs/collector.rs
@@ -0,0 +1,138 @@
+use crate::common::diagnostics::{Diagnostic, DiagnosticBundle, DiagnosticLevel};
+use crate::frontends::pbs::ast::*;
+use crate::frontends::pbs::symbols::*;
+
+pub struct SymbolCollector {
+    type_symbols: SymbolTable,
+    value_symbols: SymbolTable,
+    diagnostics: Vec<Diagnostic>,
+}
+
+impl SymbolCollector {
+    pub fn new() -> Self {
+        Self {
+            type_symbols: SymbolTable::new(),
+            value_symbols: SymbolTable::new(),
+            diagnostics: Vec::new(),
+        }
+    }
+
+    pub fn collect(&mut self, file: &FileNode) -> Result<(SymbolTable, SymbolTable), DiagnosticBundle> {
+        for decl in &file.decls {
+            match decl {
+                Node::FnDecl(fn_decl) => self.collect_fn(fn_decl),
+                Node::ServiceDecl(service_decl) => self.collect_service(service_decl),
+                Node::TypeDecl(type_decl) => self.collect_type(type_decl),
+                _ => {}
+            }
+        }
+
+        if !self.diagnostics.is_empty() {
+            return Err(DiagnosticBundle {
+                diagnostics: self.diagnostics.clone(),
+            });
+        }
+
+        Ok((
+            std::mem::replace(&mut self.type_symbols, SymbolTable::new()),
+            std::mem::replace(&mut self.value_symbols, SymbolTable::new()),
+        ))
+    }
+
+    fn collect_fn(&mut self, decl: &FnDeclNode) {
+        // Top-level fn are always file-private in PBS v0
+        let symbol = Symbol {
+            name: decl.name.clone(),
+            kind: SymbolKind::Function,
+            namespace: Namespace::Value,
+            visibility: Visibility::FilePrivate,
+            span: decl.span,
+        };
+        self.insert_value_symbol(symbol);
+    }
+
+    fn collect_service(&mut self, decl: &ServiceDeclNode) {
+        let vis = match decl.vis.as_str() {
+            "pub" => Visibility::Pub,
+            "mod" => Visibility::Mod,
+            _ => Visibility::FilePrivate, // Should not happen with valid parser
+        };
+        let symbol = Symbol {
+            name: decl.name.clone(),
+            kind: SymbolKind::Service,
+            namespace: Namespace::Type, // Service is a type
+            visibility: vis,
+            span: decl.span,
+        };
+        self.insert_type_symbol(symbol);
+    }
+
+    fn collect_type(&mut self, decl: &TypeDeclNode) {
+        let vis = match decl.vis.as_deref() {
+            Some("pub") => Visibility::Pub,
+            Some("mod") => Visibility::Mod,
+            _ => Visibility::FilePrivate,
+        };
+        let kind = match decl.type_kind.as_str() {
+            "struct" => SymbolKind::Struct,
+            "contract" => SymbolKind::Contract,
+            "error" => SymbolKind::ErrorType,
+            _ => SymbolKind::Struct, // Default
+        };
+        let symbol = Symbol {
+            name: decl.name.clone(),
+            kind,
+            namespace: Namespace::Type,
+            visibility: vis,
+            span: decl.span,
+        };
+        self.insert_type_symbol(symbol);
+    }
+
+    fn insert_type_symbol(&mut self, symbol: Symbol) {
+        // Check for collision in value namespace first
+        if let Some(existing) = self.value_symbols.get(&symbol.name) {
+            let existing = existing.clone();
+            self.error_collision(&symbol, &existing);
+            return;
+        }
+
+        if let Err(existing) = self.type_symbols.insert(symbol.clone()) {
+            self.error_duplicate(&symbol, &existing);
+        }
+    }
+
+    fn insert_value_symbol(&mut self, symbol: Symbol) {
+        // Check for collision in type namespace first
+        if let Some(existing) = self.type_symbols.get(&symbol.name) {
+            let existing = existing.clone();
+            self.error_collision(&symbol, &existing);
+            return;
+        }
+
+        if let Err(existing) = self.value_symbols.insert(symbol.clone()) {
+            self.error_duplicate(&symbol, &existing);
+        }
+    }
+
+    fn error_duplicate(&mut self, symbol: &Symbol, existing: &Symbol) {
+        self.diagnostics.push(Diagnostic {
+            level: DiagnosticLevel::Error,
+            code: Some("E_RESOLVE_DUPLICATE_SYMBOL".to_string()),
+            message: format!("Duplicate symbol '{}' already defined at {:?}", symbol.name, existing.span),
+            span: Some(symbol.span),
+        });
+    }
+
+    fn error_collision(&mut self, symbol: &Symbol, existing: &Symbol) {
+        self.diagnostics.push(Diagnostic {
+            level: DiagnosticLevel::Error,
+            code: Some("E_RESOLVE_NAMESPACE_COLLISION".to_string()),
+            message: format!(
+                "Symbol '{}' collides with another symbol in the {:?} namespace defined at {:?}",
+                symbol.name, existing.namespace, existing.span
+            ),
+            span: Some(symbol.span),
+        });
+    }
+}
diff --git a/crates/prometeu-compiler/src/frontends/pbs/resolver.rs b/crates/prometeu-compiler/src/frontends/pbs/resolver.rs
new file mode 100644
index 00000000..73b92c1f
--- /dev/null
+++ b/crates/prometeu-compiler/src/frontends/pbs/resolver.rs
@@ -0,0 +1,319 @@
+use crate::common::diagnostics::{Diagnostic, DiagnosticBundle, DiagnosticLevel};
+use crate::common::spans::Span;
+use crate::frontends::pbs::ast::*;
+use crate::frontends::pbs::symbols::*;
+use std::collections::HashMap;
+
+pub trait ModuleProvider {
+    fn get_module_symbols(&self, from_path: &str) -> Option<&ModuleSymbols>;
+}
+
+pub struct Resolver<'a> {
+    module_provider: &'a dyn ModuleProvider,
+    current_module: &'a ModuleSymbols,
+    scopes: Vec<HashMap<String, Symbol>>,
+    imported_symbols: ModuleSymbols,
+    diagnostics: Vec<Diagnostic>,
+}
+
+impl<'a> Resolver<'a> {
+    pub fn new(
+        current_module: &'a ModuleSymbols,
+        module_provider: &'a dyn ModuleProvider,
+    ) -> Self {
+        Self {
+            module_provider,
+            current_module,
+            scopes: Vec::new(),
+            imported_symbols: ModuleSymbols::new(),
+            diagnostics: Vec::new(),
+        }
+    }
+
+    pub fn resolve(&mut self, file: &FileNode) -> Result<(), DiagnosticBundle> {
+        // Step 1: Process imports to populate imported_symbols
+        for imp in &file.imports {
+            if let Node::Import(imp_node) = imp {
+                self.resolve_import(imp_node);
+            }
+        }
+
+        // Step 2: Resolve all top-level declarations
+        for decl in &file.decls {
+            self.resolve_node(decl);
+        }
+
+        if !self.diagnostics.is_empty() {
+            return Err(DiagnosticBundle {
+                diagnostics: self.diagnostics.clone(),
+            });
+        }
+
+        Ok(())
+    }
+
+    fn resolve_import(&mut self, imp: &ImportNode) {
+        let provider = self.module_provider;
+        if let Some(target_symbols) = provider.get_module_symbols(&imp.from) {
+            if let Node::ImportSpec(spec) = &*imp.spec {
+                for name in &spec.path {
+                    // Try to find in Type namespace
+                    if let Some(sym) = target_symbols.type_symbols.get(name) {
+                        if sym.visibility == Visibility::Pub {
+                            if let Err(_) = self.imported_symbols.type_symbols.insert(sym.clone()) {
+                                self.error_duplicate_import(name, imp.span);
+                            }
+                        } else {
+                            self.error_visibility(sym, imp.span);
+                        }
+                    } 
+                    // Try to find in Value namespace
+                    else if let Some(sym) = target_symbols.value_symbols.get(name) {
+                        if sym.visibility == Visibility::Pub {
+                            if let Err(_) = self.imported_symbols.value_symbols.insert(sym.clone()) {
+                                self.error_duplicate_import(name, imp.span);
+                            }
+                        } else {
+                            self.error_visibility(sym, imp.span);
+                        }
+                    } else {
+                        self.error_undefined(name, imp.span);
+                    }
+                }
+            }
+        } else {
+            self.diagnostics.push(Diagnostic {
+                level: DiagnosticLevel::Error,
+                code: Some("E_RESOLVE_INVALID_IMPORT".to_string()),
+                message: format!("Module not found: {}", imp.from),
+                span: Some(imp.span),
+            });
+        }
+    }
+
+    fn resolve_node(&mut self, node: &Node) {
+        match node {
+            Node::FnDecl(n) => self.resolve_fn_decl(n),
+            Node::ServiceDecl(n) => self.resolve_service_decl(n),
+            Node::TypeDecl(n) => self.resolve_type_decl(n),
+            Node::Block(n) => self.resolve_block(n),
+            Node::LetStmt(n) => self.resolve_let_stmt(n),
+            Node::ExprStmt(n) => self.resolve_node(&n.expr),
+            Node::ReturnStmt(n) => {
+                if let Some(expr) = &n.expr {
+                    self.resolve_node(expr);
+                }
+            }
+            Node::Call(n) => {
+                self.resolve_node(&n.callee);
+                for arg in &n.args {
+                    self.resolve_node(arg);
+                }
+            }
+            Node::Unary(n) => self.resolve_node(&n.expr),
+            Node::Binary(n) => {
+                self.resolve_node(&n.left);
+                self.resolve_node(&n.right);
+            }
+            Node::Cast(n) => {
+                self.resolve_node(&n.expr);
+                self.resolve_type_ref(&n.ty);
+            }
+            Node::IfExpr(n) => {
+                self.resolve_node(&n.cond);
+                self.resolve_node(&n.then_block);
+                if let Some(else_block) = &n.else_block {
+                    self.resolve_node(else_block);
+                }
+            }
+            Node::WhenExpr(n) => {
+                for arm in &n.arms {
+                    if let Node::WhenArm(arm_node) = arm {
+                        self.resolve_node(&arm_node.cond);
+                        self.resolve_node(&arm_node.body);
+                    }
+                }
+            }
+            Node::Ident(n) => {
+                self.resolve_identifier(&n.name, n.span, Namespace::Value);
+            }
+            Node::TypeName(n) => {
+                self.resolve_identifier(&n.name, n.span, Namespace::Type);
+            }
+            Node::TypeApp(n) => {
+                self.resolve_identifier(&n.base, n.span, Namespace::Type);
+                for arg in &n.args {
+                    self.resolve_type_ref(arg);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn resolve_fn_decl(&mut self, n: &FnDeclNode) {
+        self.enter_scope();
+        for param in &n.params {
+            self.resolve_type_ref(&param.ty);
+            self.define_local(&param.name, param.span, SymbolKind::Local);
+        }
+        if let Some(ret) = &n.ret {
+            self.resolve_type_ref(ret);
+        }
+        self.resolve_node(&n.body);
+        self.exit_scope();
+    }
+
+    fn resolve_service_decl(&mut self, n: &ServiceDeclNode) {
+        if let Some(ext) = &n.extends {
+            self.resolve_identifier(ext, n.span, Namespace::Type);
+        }
+        for member in &n.members {
+            if let Node::ServiceFnSig(sig) = member {
+                for param in &sig.params {
+                    self.resolve_type_ref(&param.ty);
+                }
+                self.resolve_type_ref(&sig.ret);
+            }
+        }
+    }
+
+    fn resolve_type_decl(&mut self, n: &TypeDeclNode) {
+        if let Node::TypeBody(body) = &*n.body {
+            for member in &body.members {
+                self.resolve_type_ref(&member.ty);
+            }
+        }
+    }
+
+    fn resolve_block(&mut self, n: &BlockNode) {
+        self.enter_scope();
+        for stmt in &n.stmts {
+            self.resolve_node(stmt);
+        }
+        self.exit_scope();
+    }
+
+    fn resolve_let_stmt(&mut self, n: &LetStmtNode) {
+        if let Some(ty) = &n.ty {
+            self.resolve_type_ref(ty);
+        }
+        self.resolve_node(&n.init);
+        self.define_local(&n.name, n.span, SymbolKind::Local);
+    }
+
+    fn resolve_type_ref(&mut self, node: &Node) {
+        self.resolve_node(node);
+    }
+
+    fn resolve_identifier(&mut self, name: &str, span: Span, namespace: Namespace) -> Option<Symbol> {
+        // Built-ins (minimal for v0)
+        if namespace == Namespace::Type {
+            match name {
+                "int" | "float" | "string" | "bool" | "void" | "optional" | "result" => return None,
+                _ => {}
+            }
+        }
+
+        // 1. local bindings
+        if namespace == Namespace::Value {
+            for scope in self.scopes.iter().rev() {
+                if let Some(sym) = scope.get(name) {
+                    return Some(sym.clone());
+                }
+            }
+        }
+
+        let table = if namespace == Namespace::Type {
+            &self.current_module.type_symbols
+        } else {
+            &self.current_module.value_symbols
+        };
+
+        // 2 & 3. file-private and module symbols
+        if let Some(sym) = table.get(name) {
+            return Some(sym.clone());
+        }
+
+        // 4. imported symbols
+        let imp_table = if namespace == Namespace::Type {
+            &self.imported_symbols.type_symbols
+        } else {
+            &self.imported_symbols.value_symbols
+        };
+        if let Some(sym) = imp_table.get(name) {
+            return Some(sym.clone());
+        }
+
+        self.error_undefined(name, span);
+        None
+    }
+
+    fn define_local(&mut self, name: &str, span: Span, kind: SymbolKind) {
+        let scope = self.scopes.last_mut().expect("No scope to define local");
+        
+        // Check for collision in Type namespace at top-level?
+        // Actually, the spec says "A name may not exist in both namespaces".
+        // If we want to be strict, we check current module's type symbols too.
+        if self.current_module.type_symbols.get(name).is_some() {
+             self.diagnostics.push(Diagnostic {
+                level: DiagnosticLevel::Error,
+                code: Some("E_RESOLVE_NAMESPACE_COLLISION".to_string()),
+                message: format!("Local variable '{}' collides with a type name", name),
+                span: Some(span),
+            });
+            return;
+        }
+
+        if scope.contains_key(name) {
+            self.diagnostics.push(Diagnostic {
+                level: DiagnosticLevel::Error,
+                code: Some("E_RESOLVE_DUPLICATE_SYMBOL".to_string()),
+                message: format!("Duplicate local variable '{}'", name),
+                span: Some(span),
+            });
+        } else {
+            scope.insert(name.to_string(), Symbol {
+                name: name.to_string(),
+                kind,
+                namespace: Namespace::Value,
+                visibility: Visibility::FilePrivate,
+                span,
+            });
+        }
+    }
+
+    fn enter_scope(&mut self) {
+        self.scopes.push(HashMap::new());
+    }
+
+    fn exit_scope(&mut self) {
+        self.scopes.pop();
+    }
+
+    fn error_undefined(&mut self, name: &str, span: Span) {
+        self.diagnostics.push(Diagnostic {
+            level: DiagnosticLevel::Error,
+            code: Some("E_RESOLVE_UNDEFINED".to_string()),
+            message: format!("Undefined identifier: {}", name),
+            span: Some(span),
+        });
+    }
+
+    fn error_duplicate_import(&mut self, name: &str, span: Span) {
+        self.diagnostics.push(Diagnostic {
+            level: DiagnosticLevel::Error,
+            code: Some("E_RESOLVE_DUPLICATE_SYMBOL".to_string()),
+            message: format!("Duplicate import: {}", name),
+            span: Some(span),
+        });
+    }
+
+    fn error_visibility(&mut self, sym: &Symbol, span: Span) {
+        self.diagnostics.push(Diagnostic {
+            level: DiagnosticLevel::Error,
+            code: Some("E_RESOLVE_VISIBILITY".to_string()),
+            message: format!("Symbol '{}' is not visible here", sym.name),
+            span: Some(span),
+        });
+    }
+}
diff --git a/crates/prometeu-compiler/src/frontends/pbs/symbols.rs b/crates/prometeu-compiler/src/frontends/pbs/symbols.rs
new file mode 100644
index 00000000..47868dc7
--- /dev/null
+++ b/crates/prometeu-compiler/src/frontends/pbs/symbols.rs
@@ -0,0 +1,74 @@
+use crate::common::spans::Span;
+use std::collections::HashMap;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Visibility {
+    FilePrivate,
+    Mod,
+    Pub,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum SymbolKind {
+    Function,
+    Service,
+    Struct,
+    Contract,
+    ErrorType,
+    Local,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Namespace {
+    Type,
+    Value,
+}
+
+#[derive(Debug, Clone)]
+pub struct Symbol {
+    pub name: String,
+    pub kind: SymbolKind,
+    pub namespace: Namespace,
+    pub visibility: Visibility,
+    pub span: Span,
+}
+
+#[derive(Debug, Clone)]
+pub struct SymbolTable {
+    pub symbols: HashMap<String, Symbol>,
+}
+
+#[derive(Debug, Clone)]
+pub struct ModuleSymbols {
+    pub type_symbols: SymbolTable,
+    pub value_symbols: SymbolTable,
+}
+
+impl ModuleSymbols {
+    pub fn new() -> Self {
+        Self {
+            type_symbols: SymbolTable::new(),
+            value_symbols: SymbolTable::new(),
+        }
+    }
+}
+
+impl SymbolTable {
+    pub fn new() -> Self {
+        Self {
+            symbols: HashMap::new(),
+        }
+    }
+
+    pub fn insert(&mut self, symbol: Symbol) -> Result<(), Symbol> {
+        if let Some(existing) = self.symbols.get(&symbol.name) {
+            return Err(existing.clone());
+        }
+        self.symbols.insert(symbol.name.clone(), symbol);
+        Ok(())
+    }
+
+    pub fn get(&self, name: &str) -> Option<&Symbol> {
+        self.symbols.get(name)
+    }
+}
diff --git a/crates/prometeu-compiler/tests/pbs_resolver_tests.rs b/crates/prometeu-compiler/tests/pbs_resolver_tests.rs
new file mode 100644
index 00000000..347ce42d
--- /dev/null
+++ b/crates/prometeu-compiler/tests/pbs_resolver_tests.rs
@@ -0,0 +1,196 @@
+use prometeu_compiler::frontends::pbs::*;
+use prometeu_compiler::common::files::FileManager;
+use prometeu_compiler::common::spans::Span;
+use std::path::PathBuf;
+
+fn setup_test(source: &str) -> (ast::FileNode, usize) {
+    let mut fm = FileManager::new();
+    let file_id = fm.add(PathBuf::from("test.pbs"), source.to_string());
+    let mut parser = parser::Parser::new(source, file_id);
+    (parser.parse_file().expect("Parsing failed"), file_id)
+}
+
+#[test]
+fn test_duplicate_symbols() {
+    let source = "
+        declare struct Foo {}
+        declare struct Foo {}
+    ";
+    let (ast, _) = setup_test(source);
+    let mut collector = SymbolCollector::new();
+    let result = collector.collect(&ast);
+    
+    assert!(result.is_err());
+    let bundle = result.unwrap_err();
+    assert!(bundle.diagnostics.iter().any(|d| d.code == Some("E_RESOLVE_DUPLICATE_SYMBOL".to_string())));
+}
+
+#[test]
+fn test_namespace_collision() {
+    let source = "
+        declare struct Foo {}
+        fn Foo() {}
+    ";
+    let (ast, _) = setup_test(source);
+    let mut collector = SymbolCollector::new();
+    let result = collector.collect(&ast);
+    
+    assert!(result.is_err());
+    let bundle = result.unwrap_err();
+    assert!(bundle.diagnostics.iter().any(|d| d.code == Some("E_RESOLVE_NAMESPACE_COLLISION".to_string())));
+}
+
+#[test]
+fn test_undefined_identifier() {
+    let source = "
+        fn main() {
+            let x = y;
+        }
+    ";
+    let (ast, _) = setup_test(source);
+    let mut collector = SymbolCollector::new();
+    let (ts, vs) = collector.collect(&ast).expect("Collection failed");
+    let ms = ModuleSymbols { type_symbols: ts, value_symbols: vs };
+    
+    struct EmptyProvider;
+    impl ModuleProvider for EmptyProvider {
+        fn get_module_symbols(&self, _path: &str) -> Option<&ModuleSymbols> { None }
+    }
+    
+    let mut resolver = Resolver::new(&ms, &EmptyProvider);
+    let result = resolver.resolve(&ast);
+    
+    assert!(result.is_err());
+    let bundle = result.unwrap_err();
+    assert!(bundle.diagnostics.iter().any(|d| d.code == Some("E_RESOLVE_UNDEFINED".to_string())));
+}
+
+#[test]
+fn test_local_variable_resolution() {
+    let source = "
+        fn main() {
+            let x = 10;
+            let y = x;
+        }
+    ";
+    let (ast, _) = setup_test(source);
+    let mut collector = SymbolCollector::new();
+    let (ts, vs) = collector.collect(&ast).expect("Collection failed");
+    let ms = ModuleSymbols { type_symbols: ts, value_symbols: vs };
+    
+    struct EmptyProvider;
+    impl ModuleProvider for EmptyProvider {
+        fn get_module_symbols(&self, _path: &str) -> Option<&ModuleSymbols> { None }
+    }
+    
+    let mut resolver = Resolver::new(&ms, &EmptyProvider);
+    let result = resolver.resolve(&ast);
+    
+    assert!(result.is_ok());
+}
+
+#[test]
+fn test_visibility_error() {
+    let source = "
+        import PrivateType from \"./other.pbs\"
+        fn main() {}
+    ";
+    let (ast, _) = setup_test(source);
+    let mut collector = SymbolCollector::new();
+    let (ts, vs) = collector.collect(&ast).expect("Collection failed");
+    let ms = ModuleSymbols { type_symbols: ts, value_symbols: vs };
+    
+    struct MockProvider {
+        other: ModuleSymbols,
+    }
+    impl ModuleProvider for MockProvider {
+        fn get_module_symbols(&self, path: &str) -> Option<&ModuleSymbols> {
+            if path == "./other.pbs" { Some(&self.other) } else { None }
+        }
+    }
+    
+    let mut other_ts = SymbolTable::new();
+    other_ts.insert(Symbol {
+        name: "PrivateType".to_string(),
+        kind: SymbolKind::Struct,
+        namespace: Namespace::Type,
+        visibility: Visibility::FilePrivate,
+        span: Span::new(1, 0, 0),
+    }).unwrap();
+    
+    let mock_provider = MockProvider {
+        other: ModuleSymbols { type_symbols: other_ts, value_symbols: SymbolTable::new() },
+    };
+    
+    let mut resolver = Resolver::new(&ms, &mock_provider);
+    let result = resolver.resolve(&ast);
+    
+    assert!(result.is_err());
+    let bundle = result.unwrap_err();
+    assert!(bundle.diagnostics.iter().any(|d| d.code == Some("E_RESOLVE_VISIBILITY".to_string())));
+}
+
+#[test]
+fn test_import_resolution() {
+    let source = "
+        import PubType from \"./other.pbs\"
+        fn main() {
+            let x: PubType = 10;
+        }
+    ";
+    let (ast, _) = setup_test(source);
+    let mut collector = SymbolCollector::new();
+    let (ts, vs) = collector.collect(&ast).expect("Collection failed");
+    let ms = ModuleSymbols { type_symbols: ts, value_symbols: vs };
+    
+    struct MockProvider {
+        other: ModuleSymbols,
+    }
+    impl ModuleProvider for MockProvider {
+        fn get_module_symbols(&self, path: &str) -> Option<&ModuleSymbols> {
+            if path == "./other.pbs" { Some(&self.other) } else { None }
+        }
+    }
+    
+    let mut other_ts = SymbolTable::new();
+    other_ts.insert(Symbol {
+        name: "PubType".to_string(),
+        kind: SymbolKind::Struct,
+        namespace: Namespace::Type,
+        visibility: Visibility::Pub,
+        span: Span::new(1, 0, 0),
+    }).unwrap();
+    
+    let mock_provider = MockProvider {
+        other: ModuleSymbols { type_symbols: other_ts, value_symbols: SymbolTable::new() },
+    };
+    
+    let mut resolver = Resolver::new(&ms, &mock_provider);
+    let result = resolver.resolve(&ast);
+    
+    assert!(result.is_ok());
+}
+
+#[test]
+fn test_invalid_import_module_not_found() {
+    let source = "
+        import NonExistent from \"./missing.pbs\"
+        fn main() {}
+    ";
+    let (ast, _) = setup_test(source);
+    let mut collector = SymbolCollector::new();
+    let (ts, vs) = collector.collect(&ast).expect("Collection failed");
+    let ms = ModuleSymbols { type_symbols: ts, value_symbols: vs };
+    
+    struct EmptyProvider;
+    impl ModuleProvider for EmptyProvider {
+        fn get_module_symbols(&self, _path: &str) -> Option<&ModuleSymbols> { None }
+    }
+    
+    let mut resolver = Resolver::new(&ms, &EmptyProvider);
+    let result = resolver.resolve(&ast);
+    
+    assert!(result.is_err());
+    let bundle = result.unwrap_err();
+    assert!(bundle.diagnostics.iter().any(|d| d.code == Some("E_RESOLVE_INVALID_IMPORT".to_string())));
+}