diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..ab5ef8f
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,2 @@
+# Every PR adds an entry at the top of Completed Steps; union keeps both sides.
+TODO.md merge=union
diff --git a/TODO.md b/TODO.md
index 3f5d942..2ed7c84 100644
--- a/TODO.md
+++ b/TODO.md
@@ -21,6 +21,12 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-10-04: Added a root `.gitattributes` that merges `TODO.md` with git's
+  union merge (issue 98), so two branches that each add an entry at the top of
+  Completed Steps merge with both entries kept instead of conflicting. The cost
+  is that a real conflict elsewhere in `TODO.md` is no longer reported: both
+  versions of the line are kept. It applies to this repository only; nothing
+  canonical changed.
 - 2026-10-04: The note under the canonical Go `Dockerfile` example in
   `REPO_POLICIES.md` now installs lint-phase system libraries with `apt-get`
   under their Debian package names (issue 83). The `golangci/golangci-lint`