docs: add PR #19 update summary

Author: gb250e

notes/pr19_update_summary.md

@@ -0,0 +1,13 @@
+# PR #19 Update Summary
+
+## External send required gate
+
+The branch now states explicitly that no further execution-distance progress is possible until the fixed outbound dispatch packet is actually sent.
+
+## Acceptable send evidence
+
+The branch now defines what does and does not count as real send evidence.
+
+## Current label
+
+`continue_sharpening`