ci: harden backport cherry-pick against package/directory renames

.github/scripts/create-backport-branch.sh

@@ -91,7 +91,13 @@ git checkout -B "${branch}" "origin/${TARGET_BRANCH}"
 # everything turns the unmerged entries into a normal (dirty) commit.
 had_conflict=false
 conflict_files=""
-if ! git cherry-pick --no-commit "${MERGE_SHA}"; then
+# Rename-detection knobs kept identical to prepare-backport-checkout.sh so a
+# green preflight and this branch don't disagree over a package/directory
+# rename. See that script for the rationale behind each setting.
+if ! git -c merge.renameLimit=999999 \
+         -c diff.renameLimit=999999 \
+         -c merge.directoryRenames=true \
+         cherry-pick -Xrename-threshold=40% --no-commit "${MERGE_SHA}"; then
   had_conflict=true
   conflict_files="$(git diff --name-only --diff-filter=U | tr '\n' ' ')"
   log "cherry-pick conflicted in: ${conflict_files}"

.github/scripts/prepare-backport-checkout.sh

@@ -47,4 +47,15 @@ end_tree="$(git rev-parse "${end_sha}^{tree}")"
 squash_sha="$(git commit-tree -p "${start_sha}" -m "ci: squashed backport of ${commit_range}" "${end_tree}")"
 
 git checkout -B "${workspace_branch}" "origin/${target_branch}"
-git cherry-pick -x "${squash_sha}"
+# Rename-detection knobs (kept identical in create-backport-branch.sh so the
+# preflight and the branch it later builds agree): a package/directory rename
+# between main and the release branch would otherwise produce spurious
+# conflicts. Raise the rename limits so Git does not silently skip inexact
+# rename detection when many paths moved; enable directory-rename detection so
+# files this backport *adds* under an old package path follow the rename; and
+# lower the similarity threshold since a rename that also rewrites package/
+# import lines can drop a small file below the 50% default.
+git -c merge.renameLimit=999999 \
+    -c diff.renameLimit=999999 \
+    -c merge.directoryRenames=true \
+    cherry-pick -Xrename-threshold=40% -x "${squash_sha}"

.github/workflows/direct-backport-push.yml

@@ -398,7 +398,14 @@ jobs:
           git checkout -B "${TARGET_BRANCH}" "origin/${TARGET_BRANCH}"
           base_sha=$(git rev-parse HEAD)
           log "base_sha=${base_sha}"
-          if ! git cherry-pick --no-commit "${MERGE_SHA}"; then
+          # Rename-detection knobs kept identical to prepare-backport-checkout.sh
+          # (the preflight) so a rename resolved cleanly there does not conflict
+          # here on the straight-to-release cherry-pick. See that script for the
+          # rationale behind each setting.
+          if ! git -c merge.renameLimit=999999 \
+                   -c diff.renameLimit=999999 \
+                   -c merge.directoryRenames=true \
+                   cherry-pick -Xrename-threshold=40% --no-commit "${MERGE_SHA}"; then
             endgroup
             group "Conflict diagnosis"
             conflicts=$(git diff --name-only --diff-filter=U)