diff --git a/src/graph/dependencies.rs b/src/graph/dependencies.rs
index c0d30ab..0e442f1 100644
--- a/src/graph/dependencies.rs
+++ b/src/graph/dependencies.rs
@@ -417,4 +417,71 @@ mod tests {
         // Verify we can get a summary
         assert!(report.unique_count() > 0);
     }
+
+    #[test]
+    fn test_extract_flow_and_apex_method_dependencies() {
+        // An agent with a flow:// action and an apex://Class.method action should
+        // populate the flows and apex_classes sets correctly, and be queryable via
+        // get_by_type and get_by_topic.
+        let source = r#"config:
+   agent_name: "Test"
+
+topic main:
+   description: "Main topic"
+
+   actions:
+      fetch_order:
+         description: "Fetch an order via a Flow"
+         inputs:
+            id: string
+               description: "Order ID"
+         outputs:
+            status: string
+               description: "Order status"
+         target: "flow://FetchOrder"
+
+      classify_order:
+         description: "Classify the order via Apex"
+         inputs:
+            id: string
+               description: "Order ID"
+         outputs:
+            label: string
+               description: "Classification label"
+         target: "apex://OrderClassifier.classify"
+
+   reasoning:
+      instructions: "Help the user"
+"#;
+        let ast = crate::parse(source).expect("Failed to parse source");
+        let report = extract_dependencies(&ast);
+
+        // Flow dependency is extracted correctly
+        assert!(report.uses_flow("FetchOrder"), "FetchOrder should be in flows");
+        assert!(report.flows.contains("FetchOrder"), "FetchOrder should be in the flows set");
+
+        // Apex method dependency extracts the class name
+        assert!(
+            report.uses_apex_class("OrderClassifier"),
+            "OrderClassifier should be in apex_classes"
+        );
+        assert!(
+            report.apex_classes.contains("OrderClassifier"),
+            "OrderClassifier should be in the apex_classes set"
+        );
+
+        // get_by_type grouping must include both flow and apex_method categories
+        let flow_deps = report.get_by_type("flow");
+        assert_eq!(flow_deps.len(), 1, "Expected 1 flow dependency");
+
+        let apex_deps = report.get_by_type("apex_method");
+        assert_eq!(apex_deps.len(), 1, "Expected 1 apex_method dependency");
+
+        // get_by_topic groups all action dependencies under "main"
+        let main_deps = report.get_by_topic("main");
+        assert_eq!(main_deps.len(), 2, "Expected 2 total dependencies in topic main");
+
+        // unique_count reflects all distinct dependency entries
+        assert!(report.unique_count() >= 2, "Expected at least 2 unique dependencies");
+    }
 }
diff --git a/src/graph/queries.rs b/src/graph/queries.rs
index 7508e45..c7b513f 100644
--- a/src/graph/queries.rs
+++ b/src/graph/queries.rs
@@ -347,4 +347,181 @@ topic main:
         // At least one edge should exist (the Routes edge from start_agent → main)
         assert!(graph.edge_count() > 0, "Expected at least one edge in the graph");
     }
+
+    #[test]
+    fn test_find_variable_readers_returns_reasoning_action() {
+        // A reasoning action that binds @variables.order_id via a with clause
+        // must show up as a reader of the order_id variable.
+        let source = r#"config:
+   agent_name: "Test"
+
+variables:
+   order_id: mutable string = ""
+      description: "Order ID used throughout the topic"
+
+topic main:
+   description: "Main topic"
+
+   actions:
+      lookup_order:
+         description: "Look up an order"
+         inputs:
+            id: string
+               description: "The order identifier"
+         outputs:
+            status: string
+               description: "Order status"
+         target: "flow://LookupOrder"
+
+   reasoning:
+      instructions: "Help the user"
+      actions:
+         do_lookup: @actions.lookup_order
+            description: "Perform the lookup"
+            with id=@variables.order_id
+"#;
+        let graph = parse_and_build(source);
+        let var_idx = graph.get_variable("order_id").expect("order_id variable not found");
+        let readers = graph.find_variable_readers(var_idx);
+        assert!(!readers.is_empty(), "Expected at least one reader of order_id");
+        // The reasoning action 'do_lookup' is the only reader
+        assert_eq!(readers.len(), 1, "Expected exactly one reader of order_id");
+    }
+
+    #[test]
+    fn test_find_variable_writers_returns_reasoning_action() {
+        // A reasoning action with `set @variables.status = @outputs.result` must
+        // show up as a writer of the status variable.
+        let source = r#"config:
+   agent_name: "Test"
+
+variables:
+   status: mutable string = ""
+      description: "Computed status written by a reasoning action"
+
+topic main:
+   description: "Main topic"
+
+   actions:
+      check:
+         description: "Run a status check"
+         inputs:
+            id: string
+               description: "Record ID"
+         outputs:
+            result: string
+               description: "Check result"
+         target: "flow://Check"
+
+   reasoning:
+      instructions: "Help the user"
+      actions:
+         do_check: @actions.check
+            description: "Run a status check"
+            with id=...
+            set @variables.status = @outputs.result
+"#;
+        let graph = parse_and_build(source);
+        let var_idx = graph.get_variable("status").expect("status variable not found");
+        let writers = graph.find_variable_writers(var_idx);
+        assert!(!writers.is_empty(), "Expected at least one writer of status");
+        assert_eq!(writers.len(), 1, "Expected exactly one writer of status");
+    }
+
+    #[test]
+    fn test_find_action_invokers_returns_reasoning_action() {
+        // A reasoning action that references @actions.get_data is an invoker
+        // of the get_data action definition; find_action_invokers should return it.
+        let source = r#"config:
+   agent_name: "Test"
+
+topic main:
+   description: "Main topic"
+
+   actions:
+      get_data:
+         description: "Fetch a record"
+         inputs:
+            id: string
+               description: "Record ID"
+         outputs:
+            result: string
+               description: "Fetched result"
+         target: "flow://GetData"
+
+   reasoning:
+      instructions: "Help the user"
+      actions:
+         fetch: @actions.get_data
+            description: "Fetch the record"
+"#;
+        let graph = parse_and_build(source);
+        let action_def_idx =
+            graph.get_action_def("main", "get_data").expect("get_data action def not found");
+        let invokers = graph.find_action_invokers(action_def_idx);
+        assert!(!invokers.is_empty(), "Expected at least one invoker of get_data");
+        // Only one reasoning action references get_data
+        assert_eq!(invokers.len(), 1, "Expected exactly one invoker of get_data");
+    }
+
+    #[test]
+    fn test_get_topic_reasoning_actions_returns_all_actions_in_topic() {
+        // get_topic_reasoning_actions("main") must return every reasoning action
+        // declared inside topic main's reasoning block.
+        let source = r#"config:
+   agent_name: "Test"
+
+topic main:
+   description: "Main topic"
+   reasoning:
+      instructions: "Help the user"
+      actions:
+         escalate: @utils.escalate
+            description: "Escalate to a human agent"
+         go_other: @utils.transition to @topic.other
+            description: "Switch to the other topic"
+
+topic other:
+   description: "Other topic"
+   reasoning:
+      instructions: "Handle other"
+"#;
+        let graph = parse_and_build(source);
+        let reasoning_actions = graph.get_topic_reasoning_actions("main");
+        // topic main has two reasoning actions: escalate and go_other
+        assert_eq!(reasoning_actions.len(), 2, "Expected 2 reasoning actions in topic main");
+        // topic other has no reasoning actions — it should return an empty list
+        assert_eq!(
+            graph.get_topic_reasoning_actions("other").len(),
+            0,
+            "topic other has no reasoning actions; its count must not bleed into main"
+        );
+    }
+
+    #[test]
+    fn test_get_topic_action_defs_returns_all_defs_in_topic() {
+        // get_topic_action_defs("main") must return every action definition
+        // declared inside topic main's actions block.
+        let source = r#"config:
+   agent_name: "Test"
+
+topic main:
+   description: "Main topic"
+
+   actions:
+      first_action:
+         description: "First action"
+         target: "flow://First"
+      second_action:
+         description: "Second action"
+         target: "flow://Second"
+
+   reasoning:
+      instructions: "Help the user"
+"#;
+        let graph = parse_and_build(source);
+        let action_defs = graph.get_topic_action_defs("main");
+        // topic main has exactly two action definitions
+        assert_eq!(action_defs.len(), 2, "Expected 2 action defs in topic main");
+    }
 }
diff --git a/tests/integration_test.rs b/tests/integration_test.rs
index f5db09b..c1755f0 100644
--- a/tests/integration_test.rs
+++ b/tests/integration_test.rs
@@ -271,4 +271,32 @@ topic main:
             .collect();
         assert!(tokens.iter().any(|t| matches!(t, lexer::Token::Config)));
     }
+
+    #[test]
+    fn test_parse_source_returns_error_for_unknown_top_level_keyword() {
+        // A word that is not a valid AgentScript top-level keyword (e.g. "foobar")
+        // cannot match any block parser.  The parser's error-recovery strategy
+        // (skip_then_retry_until) generates a parse error for the skipped tokens,
+        // so parse_source must return Err.
+        let result = parse_source("foobar_keyword: \"value\"\n");
+        assert!(
+            result.is_err(),
+            "Expected Err for unknown top-level keyword, got Ok"
+        );
+        let errors = result.unwrap_err();
+        assert!(!errors.is_empty(), "Expected at least one error message in the Err result");
+    }
+
+    #[test]
+    fn test_parse_source_returns_error_for_unpaired_at_sign() {
+        // An `@` symbol at the top level with no following namespace is not valid
+        // AgentScript syntax.  It should produce at least one parse error.
+        let result = parse_source("@\n");
+        assert!(
+            result.is_err(),
+            "Expected Err for bare '@' at the top level, got Ok"
+        );
+        let errors = result.unwrap_err();
+        assert!(!errors.is_empty(), "Expected at least one error message for bare '@'");
+    }
 }