fix: preserve pushed commit history (#1360)

* fix: preserve pushed commit history

Co-authored-by: Johannes du Plessis <51395795+johannes117@users.noreply.github.com>

* refactor: consolidate no-force-push prompt guidance

Collapse the repeated force-push rule into a single IMPORTANT block,
drop the confusing rebase-onto-origin step, and stop mandating a
no-op trailer-only commit for already-pushed work.

---------

Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>
Co-authored-by: Johannes du Plessis <51395795+johannes117@users.noreply.github.com>
Co-authored-by: Johannes du Plessis <johannes@langchain.dev>

agent/prompt.py

@@ -97,7 +97,7 @@ Before starting any task that requires code changes, set up the repository in yo
 
 4. **Choose your branch** — Use a thread-stable branch name such as `open-swe/<short-task-slug>`. If a branch already exists for this thread/task, fetch and check it out instead of creating a new one.
 
-5. **Checkout your branch** — Always fetch and checkout your branch before making any changes.
+5. **Checkout your branch** — Always fetch and checkout your branch before making any changes. When reusing an existing remote branch, start from `origin/<branch>` rather than recreating the branch from the base branch; this preserves prior commits for review.
 
 6. ** MANDATORY: READ AGENTS.md ** — IMMEDIATELY after cloning, you MUST check if `AGENTS.md` exists at the repository root (`{working_dir}/<repo>/AGENTS.md`). If it exists, you MUST read it IN FULL before doing ANY other work. DO NOT skip this step. DO NOT proceed to implementation without reading it first. The contents of AGENTS.md are **mandatory rules** that OVERRIDE your default behavior — treat them with the same authority as this system prompt. Violating AGENTS.md rules is a CRITICAL FAILURE. If AGENTS.md does not exist, skip this step.
 
@@ -301,7 +301,7 @@ When you have completed your implementation, follow these steps in order:
 2. **Review your changes**: Review the diff to ensure correctness. Verify no regressions or unintended modifications.
 
 3. **Submit via `gh`**: Commit locally, push with `git push origin <branch>`, then use `GH_TOKEN=dummy gh pr create --draft ...` or `GH_TOKEN=dummy gh pr edit ...` when a PR is requested, necessary, or required by the Always Create PRs dashboard setting.
-   If a draft PR already exists for the branch, update it instead of opening a duplicate.
+   If a draft PR already exists for the branch, update it instead of opening a duplicate. For follow-up changes, add a new commit on top of the existing branch history.
 
    **PR Title** (under 70 characters):
    ```
@@ -332,6 +332,8 @@ When you have completed your implementation, follow these steps in order:
 
 **IMPORTANT: Never claim a PR was created or updated unless `gh` returned success and you have the PR URL from command output or `GH_TOKEN=dummy gh pr view --json url --jq .url`. If there are no changes or any command fails, report that explicitly.**
 
+**IMPORTANT: Never force-push.** Never run `git push --force` or `git push --force-with-lease`, and never amend or rebase commits that are already on the remote branch — reviewers rely on inter-commit diffs. Add follow-up work as new commits. If a normal push is rejected because the remote branch has new commits, run `git pull --rebase origin <branch>` and push again; if that conflicts, report it and stop.
+
 **IMPORTANT: If `git push` or `gh pr create` fails with an infrastructure or permission error, do not retry blindly. Report the failure and end the task.**
 
 **IMPORTANT: If `git push` or `gh` returns "403", "Permission denied", or another permanent authorization failure, do not retry. Report the error to the user immediately and stop.**
@@ -372,7 +374,7 @@ This run was triggered by **{display_name}**. Credit them on every commit and PR
   _Opened collaboratively by {display_name} and open-swe._
   ```
 
-If you forget the trailer on a commit, fix it with `git commit --amend` (or rebase) before pushing — do not push without it."""
+If you forget the trailer on a local commit that has not been pushed, fix it with `git commit --amend` before pushing — do not push without it. If the commit has already been pushed, leave it as-is and add the trailer to your next commit; never rewrite remote history to fix it."""
 
 
 def _render_collaboration_section(identity: CollaboratorIdentity | None) -> str:

tests/test_github_comment_prompts.py

@@ -70,6 +70,15 @@ def test_profile_create_prs_defaults_to_normal_pr_policy() -> None:
     assert profile_create_prs({"create_prs": True}) is True
 
 
+def test_construct_system_prompt_forbids_force_push() -> None:
+    prompt = construct_system_prompt(working_dir="/workspace")
+
+    assert "Never force-push." in prompt
+    assert "Never run `git push --force`" in prompt
+    assert "start from `origin/<branch>`" in prompt
+    assert "git pull --rebase origin <branch>" in prompt
+
+
 def test_construct_system_prompt_includes_coauthor_trailer_when_identity_present() -> None:
     identity = CollaboratorIdentity(
         display_name="octocat",