testdata: seed sandbox overlap base

roodboi · roodboi · commit 5377544cb84c · 2026-03-25T14:47:41.000-04:00
diff --git a/_test_data/sandbox/overlap/shared.md b/_test_data/sandbox/overlap/shared.md
@@ -0,0 +1,9 @@
+# Same-File Overlap
+
+## Section A
+
+Parent branch owns this section and introduces the file.
+
+## Section B
+
+This section will be edited by the child branch.
