diff --git a/.github/workflows/migration_version_check.yml b/.github/workflows/migration_version_check.yml
new file mode 100644
index 00000000000..db43ab0425b
--- /dev/null
+++ b/.github/workflows/migration_version_check.yml
@@ -0,0 +1,41 @@
+name: Migration Version Check
+
+on:
+  pull_request:
+    paths:
+      - 'db/migrate/**'
+
+concurrency:
+  group: pr-${{ github.workflow }}-${{ github.head_ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  migration_version_check:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 2
+
+      - name: Reject hand-written migration versions
+        run: |
+          rounded=$(git diff --name-only --diff-filter=AR HEAD^1 HEAD -- db/migrate | grep -E '^db/migrate/[0-9]{10}0000_' || true)
+          if [ -n "$rounded" ]; then
+            echo "::error::Rounded migration versions collide across branches. Regenerate with 'bundle exec rails g migration':"
+            echo "$rounded"
+            exit 1
+          fi
+
+      - name: Reject duplicate migration versions
+        run: |
+          duplicates=$(ls db/migrate | cut -d_ -f1 | sort | uniq -d)
+          if [ -n "$duplicates" ]; then
+            echo "::error::Duplicate migration versions break db:migrate:"
+            echo "$duplicates"
+            exit 1
+          fi
diff --git a/AGENTS.md b/AGENTS.md
index 3bc730befaf..4c987b8e3e1 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -44,6 +44,7 @@
 ## General Guidelines
 
 - **Database foreign keys**: Prefer Rails associations and callbacks over database foreign-key constraints. Add a database foreign key only when there is a clear need and after checking deletion behavior and production migration/locking risks. Existing foreign keys alone are not a reason to add new ones.
+- **Migrations**: Create migrations with `bundle exec rails g migration <Name>` so the version is a real timestamp. Never hand-write or round the version (e.g. `20260925000000`); rounded versions collide across branches and break `db:migrate`.
 - Prefer the smallest production-ready change that solves the current problem.
 - Build for the expected production path first. Do not add speculative guards, fallbacks, retries, or edge-case handling unless the caller can actually hit that case or production has proven it necessary.
 - Enforce eligibility and exclusivity rules at the earliest shared entry point. Do not repeat backup guards across downstream jobs, callbacks, services, or writes unless a proven independent path bypasses that point.