diff --git a/include/network/hmas_coordinator_service.hpp b/include/network/hmas_coordinator_service.hpp
index b192e38b..d3a1b95b 100644
--- a/include/network/hmas_coordinator_service.hpp
+++ b/include/network/hmas_coordinator_service.hpp
@@ -1,5 +1,6 @@
 #pragma once
 
+#include "core/i_message_router.hpp"
 #include "network/service_registry.hpp"
 #include "network/task_phase_utils.hpp"
 #include "network/task_router.hpp"
@@ -104,6 +105,11 @@ class HMASCoordinatorServiceImpl final : public hmas::HMASCoordinator::Service {
   /// @return Number of tasks cleaned up
   int32_t cleanupOldTasks(int64_t age_threshold_ms = 3600000);  // Default: 1 hour
 
+  /// Set the message router used to notify agents of task lifecycle events.
+  /// When set, CancelTask sends a CANCEL_TASK KeystoneMessage to the assigned agent.
+  /// @param router Pointer to IMessageRouter (must outlive this object; may be nullptr)
+  void setMessageRouter(core::IMessageRouter* router);
+
  private:
   /// Generate unique task ID
   std::string generateTaskId() const;
@@ -111,6 +117,10 @@ class HMASCoordinatorServiceImpl final : public hmas::HMASCoordinator::Service {
   std::shared_ptr<ServiceRegistry> registry_;
   std::shared_ptr<TaskRouter> router_;
 
+  /// Optional message router for agent notifications (e.g., cancellation).
+  /// Not owned by this object.
+  core::IMessageRouter* message_router_{nullptr};
+
   /// Active tasks map: task_id -> TaskState
   std::unordered_map<std::string, TaskState> active_tasks_;
 
diff --git a/include/network/task_phase_utils.hpp b/include/network/task_phase_utils.hpp
index 543fbc6d..85847361 100644
--- a/include/network/task_phase_utils.hpp
+++ b/include/network/task_phase_utils.hpp
@@ -74,8 +74,18 @@ inline hmas::TaskPhase stringToPhase(const std::string& phase_str) {
     return hmas::TASK_PHASE_CANCELLED;
   if (phase_str == "ERROR")
     return hmas::TASK_PHASE_ERROR;
-
+  if (phase_str == "UNSPECIFIED")
+    return hmas::TASK_PHASE_UNSPECIFIED;
   return hmas::TASK_PHASE_UNSPECIFIED;
 }
 
+/// Returns true if the string maps to a known (non-UNSPECIFIED) TaskPhase value.
+inline bool isKnownPhaseString(const std::string& phase_str) {
+  if (phase_str.empty())
+    return false;
+  if (phase_str == "UNSPECIFIED")
+    return false;
+  return stringToPhase(phase_str) != hmas::TASK_PHASE_UNSPECIFIED;
+}
+
 }  // namespace keystone::network
diff --git a/src/network/yaml_parser.cpp b/src/network/yaml_parser.cpp
index cf64bca8..35cc5902 100644
--- a/src/network/yaml_parser.cpp
+++ b/src/network/yaml_parser.cpp
@@ -1,7 +1,10 @@
 #include "network/yaml_parser.hpp"
 
+#include "network/task_phase_utils.hpp"
+
 #include <regex>
 #include <sstream>
+#include <stdexcept>
 
 namespace keystone::network {
 
@@ -53,6 +56,8 @@ std::optional<HierarchicalTaskSpec> YamlParser::parseTaskSpec(const YAML::Node&
     return spec;
   } catch (const YAML::Exception& e) {
     return std::nullopt;
+  } catch (const std::exception& e) {
+    return std::nullopt;
   }
 }
 
@@ -297,7 +302,14 @@ TaskStatus YamlParser::parseStatus(const YAML::Node& node) {
   TaskStatus status;
 
   if (node["phase"]) {
-    status.phase = node["phase"].as<std::string>();
+    const std::string phase_str = node["phase"].as<std::string>();
+    // Validate phase string against the known TaskPhase enum values.
+    // An empty string defaults to "PENDING" (struct default); any non-empty
+    // string that does not map to a valid phase is rejected.
+    if (!phase_str.empty() && !isKnownPhaseString(phase_str)) {
+      throw std::runtime_error("Unknown task phase string: '" + phase_str + "'");
+    }
+    status.phase = phase_str;
   }
   if (node["startTime"]) {
     status.start_time = node["startTime"].as<std::string>();