Fix stuck PRs from incomplete conflict-resolution comment

When updating a descendant branch after its parent PR was squash-merged
hits a merge conflict, the bot posts a comment telling the author how to
finish by hand. That comment listed only the ref that conflicted, so a
human following it ran a single `git merge` and ended up with a branch
still missing the parent-branch merge and the `-s ours` squash record —
never mergeable into its new base, so it stayed stuck.

The sequence is the same whichever merge conflicts, so the comment now
prints it in full: merge the parent branch, merge the pre-squash target,
then record the squash with `-s ours`. This fixes the comment only; the
author runs the steps by hand.

The e2e conflict scenario used to resolve by merging the base directly,
so it never exercised the comment. It now follows the comment's commands
verbatim, proving a human who follows them ends up mergeable.

Diagnosed on sensei #7987.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Phlogistique

tests/test_e2e.sh

@@ -878,32 +878,37 @@ else
 fi
 
 
-# 12. Resolve conflict manually
-echo >&2 "12. Resolving conflict manually on feature3..."
+# 12. Resolve the conflict by following the comment the action posted.
+echo >&2 "12. Resolving conflict on feature3 by following the posted comment..."
 log_cmd git checkout feature3
-# Ensure we have the latest main which includes the PR2 merge commit AND the conflicting change on main
 log_cmd git fetch origin
-# Now, perform the merge that the action tried and failed
-echo >&2 "Attempting merge of origin/main into feature3..."
-if git merge origin/main; then
-    echo >&2 "❌ Conflict Resolution Failed: Merge of main into feature3 succeeded unexpectedly (no conflict?)"
-    log_cmd git status
-    log_cmd git log --graph --oneline --all
+# Run the merge commands from the comment verbatim, resolving any conflict by
+# keeping feature3's side. Following the comment must leave feature3 cleanly
+# mergeable into its new base; otherwise the synchronize-triggered continuation
+# can never make progress and the conflict label stays stuck.
+COMMENT_MERGES=$(echo "$CONFLICT_COMMENT" | grep -E '^git merge' || true)
+if [[ -z "$COMMENT_MERGES" ]]; then
+    echo >&2 "❌ Verification Failed: conflict comment lists no 'git merge' commands to follow."
+    echo >&2 "$CONFLICT_COMMENT"
+    exit 1
+fi
+HIT_CONFLICT=false
+while IFS= read -r cmd; do
+    echo >&2 "Following comment: $cmd"
+    if ! log_cmd bash -c "$cmd"; then
+        echo >&2 "Conflict during '$cmd'; resolving by keeping feature3's side..."
+        log_cmd git checkout --ours file.txt
+        log_cmd git add file.txt
+        log_cmd git commit --no-edit
+        HIT_CONFLICT=true
+    fi
+done <<< "$COMMENT_MERGES"
+if [[ "$HIT_CONFLICT" != "true" ]]; then
+    echo >&2 "❌ Verification Failed: following the comment hit no conflict; scenario expected one."
     exit 1
-else
-    echo >&2 "Merge conflict occurred as expected. Resolving..."
-    # Check status to confirm conflict
-    log_cmd git status
-    # Resolve conflict - keep feature3's version (ours) of the conflicting file
-    # This preserves both line 2 (Feature 3 content) and line 7 (Feature 3 conflicting change)
-    log_cmd git checkout --ours file.txt
-    echo "Resolved file.txt content:"
-    cat file.txt
-    log_cmd git add file.txt
-    # Use 'git commit' without '-m' to use the default merge commit message
-    log_cmd git commit --no-edit
-    echo >&2 "Conflict resolved and committed."
 fi
+echo >&2 "Resolved file.txt content:"
+cat file.txt
 log_cmd git push origin feature3
 echo >&2 "Pushed resolved feature3."
 

update-pr-stack.sh

@@ -45,17 +45,6 @@ has_squash_commit() {
         && git merge-base --is-ancestor SQUASH_COMMIT "$BRANCH"
 }
 
-format_branch_list_for_text() {
-    for ((i=1; i<=$#; i++)); do
-        case $i in
-            1) format='`%s`';;
-            $#) format=', and `%s`';;
-            *) format=', `%s`';;
-        esac
-        printf "$format" "${!i}"
-    done
-}
-
 update_direct_target() {
     local BRANCH="$1"
     local BASE_BRANCH="$2"
@@ -91,24 +80,21 @@ update_direct_target() {
         {
             echo "### ⚠️ Automatic update blocked by merge conflicts"
             echo
-            echo -n "I tried to merge "
-            format_branch_list_for_text "${CONFLICTS[@]}"
-            echo " into this branch while updating the pull request stack and hit conflicts."
+            echo "I hit a merge conflict while updating this pull request after its base branch was squash-merged. Please resolve it by hand by running these in order:"
             echo
             echo "#### How to resolve"
             echo '```bash'
             echo "git fetch origin"
             echo "git switch $BRANCH"
-            for conflict in "${CONFLICTS[@]}"; do
-                echo "git merge $conflict"
-                echo "# ..."
-                echo '# fix conflicts, for instance with `git mergetool`'
-                echo "# ..."
-                echo "git commit"
-            done
+            echo "git merge origin/$MERGED_BRANCH"
+            echo "git merge $(git rev-parse SQUASH_COMMIT~)"
+            echo "# record the squash commit as merged without re-applying its changes:"
+            echo "git merge -s ours $(git rev-parse SQUASH_COMMIT)"
             echo "git push"
             echo '```'
             echo
+            echo 'If a merge stops with conflicts, fix them (for instance with `git mergetool`), `git commit`, then run the next command.'
+            echo
             echo "Once you push, this action will resume and finish updating this pull request."
         } | log_cmd gh pr comment "$BRANCH" -F -
         # Create the label if it doesn't exist, then add it to the PR