diff --git a/tests/profile_test.rs b/tests/profile_test.rs
new file mode 100644
index 0000000..93f2285
--- /dev/null
+++ b/tests/profile_test.rs
@@ -0,0 +1,317 @@
+use rustagent::agent::profile::AgentProfile;
+use rustagent::security::SecurityScope;
+
+#[test]
+fn test_security_scope_default_is_permissive() {
+    // P1d.AC1.2: Default SecurityScope should be permissive
+    let scope = SecurityScope::default();
+
+    assert_eq!(scope.allowed_paths, vec!["*"]);
+    assert!(scope.denied_paths.is_empty());
+    assert_eq!(scope.allowed_commands, vec!["*"]);
+    assert!(!scope.read_only);
+    assert!(scope.can_create_files);
+    assert!(!scope.network_access);
+}
+
+#[test]
+fn test_security_scope_deserialize() {
+    // P1d.AC1.2: SecurityScope can be deserialized from TOML
+    let toml_str = r#"
+        allowed_paths = ["/home/user/project"]
+        denied_paths = ["/etc"]
+        allowed_commands = ["ls", "cat"]
+        read_only = true
+        can_create_files = false
+        network_access = false
+    "#;
+
+    let scope: SecurityScope = toml::from_str(toml_str).expect("Failed to deserialize");
+
+    assert_eq!(scope.allowed_paths, vec!["/home/user/project"]);
+    assert_eq!(scope.denied_paths, vec!["/etc"]);
+    assert_eq!(scope.allowed_commands, vec!["ls", "cat"]);
+    assert!(scope.read_only);
+    assert!(!scope.can_create_files);
+    assert!(!scope.network_access);
+}
+
+#[test]
+fn test_agent_profile_deserialize() {
+    // P1d.AC3.1: AgentProfile deserializes from TOML
+    let toml_str = r#"
+        name = "coder"
+        role = "Implementation specialist"
+        system_prompt = "You are a code implementation specialist"
+        allowed_tools = ["file", "shell"]
+        turn_limit = 50
+        token_budget = 100000
+
+        [security]
+        allowed_paths = ["/project"]
+        denied_paths = []
+        allowed_commands = ["ls", "cat"]
+        read_only = false
+        can_create_files = true
+        network_access = false
+
+        [llm]
+        model = "claude-3-sonnet-20250219"
+        temperature = 0.7
+        max_tokens = 4096
+    "#;
+
+    let profile: AgentProfile = toml::from_str(toml_str).expect("Failed to deserialize");
+
+    assert_eq!(profile.name, "coder");
+    assert_eq!(profile.role, "Implementation specialist");
+    assert_eq!(profile.system_prompt, "You are a code implementation specialist");
+    assert_eq!(profile.allowed_tools, vec!["file", "shell"]);
+    assert_eq!(profile.turn_limit, Some(50));
+    assert_eq!(profile.token_budget, Some(100000));
+    assert_eq!(profile.security.allowed_paths, vec!["/project"]);
+    assert_eq!(profile.security.allowed_commands, vec!["ls", "cat"]);
+    assert_eq!(profile.llm.model, Some("claude-3-sonnet-20250219".to_string()));
+    assert_eq!(profile.llm.temperature, Some(0.7));
+    assert_eq!(profile.llm.max_tokens, Some(4096));
+}
+
+#[test]
+fn test_agent_profile_inheritance_scalar_fields() {
+    // P1d.AC3.5: Scalar fields - child wins if non-empty
+    let mut child = AgentProfile {
+        name: "child".to_string(),
+        extends: Some("parent".to_string()),
+        role: "Child role".to_string(),
+        system_prompt: "child prompt".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    let parent = AgentProfile {
+        name: "parent".to_string(),
+        extends: None,
+        role: "Parent role".to_string(),
+        system_prompt: "parent prompt".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    child.apply_inheritance(&parent);
+
+    assert_eq!(child.role, "Child role");
+    assert!(child.system_prompt.contains("parent prompt"));
+    assert!(child.system_prompt.contains("child prompt"));
+}
+
+#[test]
+fn test_agent_profile_inheritance_scalar_fields_empty() {
+    // P1d.AC3.5: Scalar fields - parent used if child empty
+    let mut child = AgentProfile {
+        name: "child".to_string(),
+        extends: Some("parent".to_string()),
+        role: "".to_string(),
+        system_prompt: "child prompt".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    let parent = AgentProfile {
+        name: "parent".to_string(),
+        extends: None,
+        role: "Parent role".to_string(),
+        system_prompt: "parent prompt".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    child.apply_inheritance(&parent);
+
+    assert_eq!(child.role, "Parent role");
+}
+
+#[test]
+fn test_agent_profile_inheritance_list_fields() {
+    // P1d.AC3.5: List fields - child replaces parent entirely (not merged)
+    let mut child = AgentProfile {
+        name: "child".to_string(),
+        extends: Some("parent".to_string()),
+        role: "Child".to_string(),
+        system_prompt: "".to_string(),
+        allowed_tools: vec!["file".to_string()],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    let parent = AgentProfile {
+        name: "parent".to_string(),
+        extends: None,
+        role: "Parent".to_string(),
+        system_prompt: "".to_string(),
+        allowed_tools: vec!["file".to_string(), "shell".to_string()],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    child.apply_inheritance(&parent);
+
+    // Child has ["file"], so it should not inherit parent's ["file", "shell"]
+    assert_eq!(child.allowed_tools, vec!["file"]);
+}
+
+#[test]
+fn test_agent_profile_inheritance_list_fields_empty() {
+    // P1d.AC3.5: List fields - parent used if child empty
+    let mut child = AgentProfile {
+        name: "child".to_string(),
+        extends: Some("parent".to_string()),
+        role: "Child".to_string(),
+        system_prompt: "".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    let parent = AgentProfile {
+        name: "parent".to_string(),
+        extends: None,
+        role: "Parent".to_string(),
+        system_prompt: "".to_string(),
+        allowed_tools: vec!["file".to_string(), "shell".to_string()],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    child.apply_inheritance(&parent);
+
+    assert_eq!(child.allowed_tools, vec!["file", "shell"]);
+}
+
+#[test]
+fn test_agent_profile_inheritance_system_prompt_appends() {
+    // P1d.AC3.5: system_prompt appends with separator
+    let mut child = AgentProfile {
+        name: "child".to_string(),
+        extends: Some("parent".to_string()),
+        role: "Child".to_string(),
+        system_prompt: "Child instructions".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    let parent = AgentProfile {
+        name: "parent".to_string(),
+        extends: None,
+        role: "Parent".to_string(),
+        system_prompt: "Parent instructions".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    child.apply_inheritance(&parent);
+
+    assert!(child.system_prompt.contains("Parent instructions"));
+    assert!(child.system_prompt.contains("Project-Specific Instructions"));
+    assert!(child.system_prompt.contains("Child instructions"));
+}
+
+#[test]
+fn test_agent_profile_inheritance_optional_fields() {
+    // P1d.AC3.5: Optional fields - child Some wins, falls to parent if None
+    let mut child = AgentProfile {
+        name: "child".to_string(),
+        extends: Some("parent".to_string()),
+        role: "Child".to_string(),
+        system_prompt: "".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: Some(75),
+        token_budget: None,
+    };
+
+    let parent = AgentProfile {
+        name: "parent".to_string(),
+        extends: None,
+        role: "Parent".to_string(),
+        system_prompt: "".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: Default::default(),
+        turn_limit: Some(50),
+        token_budget: Some(200000),
+    };
+
+    child.apply_inheritance(&parent);
+
+    assert_eq!(child.turn_limit, Some(75)); // child wins
+    assert_eq!(child.token_budget, Some(200000)); // from parent
+}
+
+#[test]
+fn test_agent_profile_inheritance_llm_config() {
+    // P1d.AC3.5: LLM config - child Some wins, falls to parent if None
+    let mut child = AgentProfile {
+        name: "child".to_string(),
+        extends: Some("parent".to_string()),
+        role: "Child".to_string(),
+        system_prompt: "".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: rustagent::agent::profile::ProfileLlmConfig {
+            model: Some("child-model".to_string()),
+            temperature: None,
+            max_tokens: None,
+        },
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    let parent = AgentProfile {
+        name: "parent".to_string(),
+        extends: None,
+        role: "Parent".to_string(),
+        system_prompt: "".to_string(),
+        allowed_tools: vec![],
+        security: SecurityScope::default(),
+        llm: rustagent::agent::profile::ProfileLlmConfig {
+            model: Some("parent-model".to_string()),
+            temperature: Some(0.5),
+            max_tokens: Some(2000),
+        },
+        turn_limit: None,
+        token_budget: None,
+    };
+
+    child.apply_inheritance(&parent);
+
+    assert_eq!(child.llm.model, Some("child-model".to_string())); // child wins
+    assert_eq!(child.llm.temperature, Some(0.5)); // from parent
+    assert_eq!(child.llm.max_tokens, Some(2000)); // from parent
+}