diff --git a/lib/engine_system/mailbox/mailbox_runtime.ex b/lib/engine_system/mailbox/mailbox_runtime.ex
index a09d1e4..b0cb72d 100644
--- a/lib/engine_system/mailbox/mailbox_runtime.ex
+++ b/lib/engine_system/mailbox/mailbox_runtime.ex
@@ -262,6 +262,7 @@ defmodule EngineSystem.Mailbox.MailboxRuntime do
 
   # Execute DSL-defined behaviour patterns
   defp execute_behaviour(message, state) do
+    context_meta = message_context(message)
     # Create proper State.Configuration and State.Environment structures
     # The behavior evaluation expects these to have local_state fields
     config_struct =
@@ -277,14 +278,16 @@ defmodule EngineSystem.Mailbox.MailboxRuntime do
       {:ok, effects} ->
         case apply_effects_to_state(effects, state) do
           {:ok, updated_state} -> {:ok, effects, updated_state}
-          {:error, reason} -> {:error, reason}
+          {:error, reason} -> {:error, {:apply_effects_error, reason, context_meta}}
         end
 
       {:error, reason} ->
-        {:error, reason}
+        {:error, {:dsl_evaluation_error, reason, context_meta}}
     end
   rescue
-    exception -> {:error, {:behaviour_error, exception}}
+    exception ->
+      meta = safe_message_context(message)
+      {:error, {:behaviour_exception, exception, __STACKTRACE__, meta}}
   end
 
   # Apply effects to update mailbox state
@@ -334,4 +337,57 @@ defmodule EngineSystem.Mailbox.MailboxRuntime do
       end
     end)
   end
+
+  # Build structured metadata from a DSL message payload for better diagnostics
+  defp message_context(%Message{payload: {op, args}}) when is_atom(op),
+    do: %{behaviour: op, args: args}
+
+  defp message_context(%Message{payload: op}) when is_atom(op),
+    do: %{behaviour: op, args: nil}
+
+  defp message_context(%Message{}), do: %{behaviour: :unknown, args: nil}
+
+  defp safe_message_context(message) do
+    message_context(message)
+  rescue
+    _ -> %{behaviour: :unknown, args: nil}
+  end
+
+  defp format_behaviour_error({:behaviour_exception, exception, stacktrace, meta}) do
+    op = Map.get(meta, :behaviour, :unknown)
+    args = Map.get(meta, :args)
+
+    location =
+      case stacktrace do
+        [top | _] -> Exception.format_stacktrace_entry(top)
+        _ -> "unknown"
+      end
+
+    "- behaviour=#{inspect(op)}\n" <>
+      "  - args=#{inspect(args)}\n" <>
+      "  - error=#{Exception.message(exception)}\n" <>
+      "  - at=#{location}\n" <>
+      "  - meta=#{inspect(meta)}\n" <>
+      Exception.format_stacktrace(stacktrace)
+  end
+
+  defp format_behaviour_error({:dsl_evaluation_error, inner, meta}) do
+    op = Map.get(meta, :behaviour, :unknown)
+    args = Map.get(meta, :args)
+
+    "- behaviour=#{inspect(op)}\n" <>
+      "  - args=#{inspect(args)}\n" <>
+      "  - reason=#{inspect(inner)}\n" <>
+      "  - meta=#{inspect(meta)}\n"
+  end
+
+  defp format_behaviour_error({:apply_effects_error, inner, meta}) do
+    op = Map.get(meta, :behaviour, :unknown)
+    args = Map.get(meta, :args)
+
+    "- behaviour=#{inspect(op)}\n" <>
+      "  - args=#{inspect(args)}\n" <>
+      "  - apply_effects_error=#{inspect(inner)}\n" <>
+      "  - meta=#{inspect(meta)}\n"
+  end
 end