diff --git a/localinfra/scripts/init-data.sh b/localinfra/scripts/init-data.sh
index 175f1cf4f..f9424a368 100644
--- a/localinfra/scripts/init-data.sh
+++ b/localinfra/scripts/init-data.sh
@@ -33,6 +33,7 @@ STATE_1=at://$OWNER_DID/sh.tangled.repo.issue.state/3lzg6kgvni222
 
 PULL_1=at://$OWNER_DID/sh.tangled.repo.pull/3lzg7tkxvq222
 PULL_2=at://$OWNER_DID/sh.tangled.repo.pull/3ms6rk5d6gk22
+PULL_3=at://$OWNER_DID/sh.tangled.repo.pull/3ms6rk5d6gk33
 
 STRING_CODE=at://$OWNER_DID/sh.tangled.string/3lzg6ma4pa222
 STRING_MARKDOWN=at://$OWNER_DID/sh.tangled.string/3lzg6nzdqy222
@@ -237,6 +238,37 @@ put_record "$PULL_2" "$(jq -nc \
     versions:[{head:$head1, base:$base, createdAt:$createdAt1},
               {head:$head2, base:$base, createdAt:$createdAt2}]}')" >/dev/null
 
+# a stale PR: sv-fe has moved on, so this base is no longer an ancestor of it
+PULL_3_BASE=a30e171f6297ac08777ce78bfea3fc9de27be8be
+PULL_3_HEAD=7a486c07f881800c5dd5eec98dfb5fb10d96bddc
+
+keep_commit "$REPO_DID" "$PULL_3_BASE" "$PULL_3"
+keep_commit "$REPO_DID" "$PULL_3_HEAD" "$PULL_3"
+
+put_record "$PULL_3" "$(jq -nc \
+  --arg repo "$REPO_DID" \
+  --arg title 'Add profile activity feed' \
+  --arg body "$(cat <<'MARKDOWN'
+Fixture for a PR whose merge-base went stale because the *target* branch moved,
+not the source:
+
+1. `sv-fe` branches off `master`
+2. `dwn/profile-activity` branches off `sv-fe` — merge-base recorded as `a30e171f`
+3. `sv-fe` is rebased wholesale onto a newer `master`
+4. `a30e171f` is no longer an ancestor of `sv-fe`, so the recorded base is stale
+
+This is why the diff says 62 files changed while merge-check says 1155 conflicted files
+MARKDOWN
+)" \
+  --arg head "$PULL_3_HEAD" \
+  --arg base "$PULL_3_BASE" \
+  --arg createdAt '2025-09-22T10:44:35Z' \
+  '{title:$title, body:$body, createdAt:$createdAt,
+    source:{repo:$repo, branch:"dwn/profile-activity"},
+    target:{repo:$repo, branch:"sv-fe"},
+    rounds:[],
+    versions:[{head:$head, base:$base, createdAt:$createdAt}]}')" >/dev/null
+
 # --- string fixtures ---
 
 STRING_CODE_CID=$(put_record "$STRING_CODE" "$(jq -nc \