feat(runtime): record execution evidence and gate completion

tests/runtime_evidence_helpers.py

@@ -0,0 +1,10 @@
+"""Dispatcher doubles must simulate the receipt boundary as well as the result."""
+from src.agent_runtime.journal import mark_dispatch, record_action
+
+
+def authoritative_executor(function):
+    @record_action
+    async def execute(block, *args, **kwargs):
+        mark_dispatch()
+        return await function(block, *args, **kwargs)
+    return execute