[+] Force push detection & sync

Updated installation instructions and demo generation details in README.

.mailmap

@@ -0,0 +1 @@
+Azalea <noreply@aza.moe> <22280294+hykilpikonna@users.noreply.github.com>

Cargo.lock

@@ -1118,7 +1118,7 @@ dependencies = [
 
 [[package]]
 name = "refray"
-version = "0.1.0"
+version = "0.1.1"
 dependencies = [
  "anyhow",
  "clap",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "refray"
-version = "0.1.0"
+version = "0.1.1"
 edition = "2024"
 authors = ["Azalea"]
 description = "∞-way read-write git mirroring tool"

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Azalea
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -240,6 +240,8 @@ Conflict resolution strategies are configured per mirror group:
 
 When a previously opened conflict pull request is merged, the next sync sees the merged branch as the winning tip, pushes it to the other endpoints, and closes stale `refray/conflicts/...` pull requests for that branch.
 
+Force-pushes are propagated only when `refray` can infer intent from the previous successful sync state. If a branch previously matched everywhere, one endpoint rewrites that branch to a non-descendant tip, and the other endpoints still have the previous tip, `refray` writes local backup refs and a bundle under the work-dir `backups/` directory before force-pushing the rewritten tip to the other endpoints. If multiple endpoints rewrite the branch differently, or another endpoint also advances independently, the branch is treated as a conflict and skipped.
+
 Repository and branch deletion are propagated only when it is safe to infer intent, and `refray` writes local backup refs and bundle files under the work-dir `backups/` directory before propagating those deletions. If a repository existed on every endpoint in the previous successful sync, then disappears from one endpoint while the remaining endpoints still have the previous synced refs, `refray` deletes it from the remaining endpoints instead of recreating it when `delete_missing = true`. If `delete_missing = false`, that missing repository is not treated as a deletion and normal missing-repository handling applies. If the repository was deleted everywhere, `refray` removes its saved sync state after creating a local backup from the mirror cache. If the repository was deleted on one endpoint but changed elsewhere, it is treated as a conflict and skipped.
 
 Branch deletion follows the same rule at branch scope: if a branch existed on every endpoint in the previous successful sync, then disappears from one endpoint while the remaining endpoints still have the previous tip, `refray` deletes it from the remaining endpoints instead of recreating it. If the branch was deleted on one endpoint but changed elsewhere, it is treated as a conflict and skipped.

src/git.rs

@@ -86,6 +86,12 @@ pub struct GitMirror {
     dry_run: bool,
 }
 
+struct CommitterIdentity {
+    name: String,
+    email: String,
+    date: String,
+}
+
 #[derive(Clone, Debug)]
 pub struct Redactor {
     secrets: Vec<String>,
@@ -582,6 +588,7 @@ impl GitMirror {
             return Ok(format!("dry-run-rebased-{}", short_sha(tip)));
         }
 
+        let commits = self.replay_commits(base, tip)?;
         let worktree = tempfile::TempDir::new().context("failed to create temporary worktree")?;
         let worktree_path = worktree.path().to_path_buf();
         self.run([
@@ -589,12 +596,13 @@ impl GitMirror {
             "add",
             "--detach",
             worktree_path.to_str().unwrap(),
-            tip,
+            onto,
         ])?;
 
-        let rebase_result = self.worktree_git(&worktree_path, ["rebase", "--onto", onto, base]);
-        if let Err(error) = rebase_result {
-            let _ = self.worktree_git(&worktree_path, ["rebase", "--abort"]);
+        let replay_result = self.replay_commits_preserving_committer(&worktree_path, &commits);
+        if let Err(error) = replay_result {
+            let _ = self.worktree_git(&worktree_path, ["cherry-pick", "--abort"]);
+            let _ = self.worktree_git(&worktree_path, ["reset", "--hard"]);
             let _ = self.run([
                 "worktree",
                 "remove",
@@ -613,6 +621,66 @@ impl GitMirror {
         Ok(rebased.trim().to_string())
     }
 
+    fn replay_commits(&self, base: &str, tip: &str) -> Result<Vec<String>> {
+        let range = format!("{base}..{tip}");
+        Ok(self
+            .output([
+                "rev-list",
+                "--reverse",
+                "--topo-order",
+                "--no-merges",
+                &range,
+            ])?
+            .lines()
+            .map(str::trim)
+            .filter(|line| !line.is_empty())
+            .map(ToOwned::to_owned)
+            .collect())
+    }
+
+    fn replay_commits_preserving_committer(
+        &self,
+        worktree: &Path,
+        commits: &[String],
+    ) -> Result<()> {
+        for commit in commits {
+            let committer = self.committer_identity(commit)?;
+            self.worktree_git(worktree, ["cherry-pick", "--no-commit", commit])?;
+            self.worktree_git_with_committer(
+                worktree,
+                ["commit", "--no-gpg-sign", "-C", commit],
+                &committer,
+            )?;
+        }
+        Ok(())
+    }
+
+    fn committer_identity(&self, commit: &str) -> Result<CommitterIdentity> {
+        let output = self.output(["show", "-s", "--format=%cn%x00%ce%x00%cI", commit])?;
+        let output = output.trim_end_matches('\n');
+        let mut parts = output.split('\0');
+        let name = parts
+            .next()
+            .filter(|value| !value.is_empty())
+            .ok_or_else(|| anyhow::anyhow!("commit {commit} has no committer name"))?;
+        let email = parts
+            .next()
+            .filter(|value| !value.is_empty())
+            .ok_or_else(|| anyhow::anyhow!("commit {commit} has no committer email"))?;
+        let date = parts
+            .next()
+            .filter(|value| !value.is_empty())
+            .ok_or_else(|| anyhow::anyhow!("commit {commit} has no committer date"))?;
+        if parts.next().is_some() {
+            bail!("commit {commit} has unexpected committer metadata");
+        }
+        Ok(CommitterIdentity {
+            name: name.to_string(),
+            email: email.to_string(),
+            date: date.to_string(),
+        })
+    }
+
     pub fn is_ancestor(&self, ancestor: &str, descendant: &str) -> Result<bool> {
         let status = self
             .command()
@@ -709,6 +777,35 @@ impl GitMirror {
             .into())
         }
     }
+
+    fn worktree_git_with_committer<const N: usize>(
+        &self,
+        worktree: &Path,
+        args: [&str; N],
+        committer: &CommitterIdentity,
+    ) -> Result<()> {
+        let output = Command::new("git")
+            .arg("-C")
+            .arg(worktree)
+            .args(args)
+            .env("GIT_COMMITTER_NAME", &committer.name)
+            .env("GIT_COMMITTER_EMAIL", &committer.email)
+            .env("GIT_COMMITTER_DATE", &committer.date)
+            .output()
+            .with_context(|| "failed to run git")?;
+        if output.status.success() {
+            Ok(())
+        } else {
+            Err(GitCommandError::new(
+                "git",
+                self.redactor
+                    .redact(&String::from_utf8_lossy(&output.stdout)),
+                self.redactor
+                    .redact(&String::from_utf8_lossy(&output.stderr)),
+            )
+            .into())
+        }
+    }
 }
 
 fn short_sha(sha: &str) -> &str {

src/sync.rs

@@ -1399,6 +1399,27 @@ fn push_repo_refs(
         fail_on_unresolved_conflict(context, "branch deletion conflict")?;
     }
 
+    let (force_pushes, force_push_conflicts, force_push_branches) =
+        branch_force_push_decisions(mirror_repo, remotes, previous_refs, current_refs)?;
+    let had_force_push_conflicts = !force_push_conflicts.is_empty();
+    for conflict in &force_push_conflicts {
+        crate::logln!(
+            "  {} branch {} has conflicting force-push changes on {} ({}, {})",
+            style("conflict").yellow().bold(),
+            style(&conflict.branch).cyan(),
+            conflict.remotes.join("+"),
+            conflict.reason,
+            style("skipped").dim()
+        );
+    }
+    if had_force_push_conflicts {
+        fail_on_unresolved_conflict(context, "branch force-push conflict")?;
+    }
+    let blocked_branches = blocked_branches
+        .union(&force_push_branches)
+        .cloned()
+        .collect::<BTreeSet<_>>();
+
     let (branches, conflicts) = mirror_repo.branch_decisions(remotes)?;
     let branches_to_push = branches
         .into_iter()
@@ -1423,6 +1444,7 @@ fn push_repo_refs(
         }
     }
     let had_branch_conflicts = !unresolved_branch_conflicts.is_empty();
+    let force_push_updates = force_push_updates(&force_pushes);
     let unresolved_branch_names = unresolved_branch_conflicts
         .iter()
         .map(|conflict| conflict.branch.clone())
@@ -1463,13 +1485,17 @@ fn push_repo_refs(
 
     let pushed_branch_names = branch_names(&branches_to_push);
     let rebased_branch_names = branch_names_from_updates(&rebased_branch_updates);
+    let force_pushed_branch_names = branch_names_from_updates(&force_push_updates);
     let mut cleanup_branches = stale_conflict_branches;
     cleanup_branches.retain(|branch| {
-        !pushed_branch_names.contains(branch) && !rebased_branch_names.contains(branch)
+        !pushed_branch_names.contains(branch)
+            && !rebased_branch_names.contains(branch)
+            && !force_pushed_branch_names.contains(branch)
     });
 
     if branches_to_push.is_empty()
         && rebased_branch_updates.is_empty()
+        && force_push_updates.is_empty()
         && tags_to_push.is_empty()
         && unresolved_branch_conflicts.is_empty()
     {
@@ -1499,7 +1525,10 @@ fn push_repo_refs(
         );
         return Ok(RepoRefSyncResult {
             pushed: false,
-            had_conflicts: had_branch_conflicts || had_tag_conflicts || had_deletion_conflicts,
+            had_conflicts: had_branch_conflicts
+                || had_tag_conflicts
+                || had_deletion_conflicts
+                || had_force_push_conflicts,
         });
     }
     if !branch_deletions.is_empty() {
@@ -1522,6 +1551,18 @@ fn push_repo_refs(
         mirror_repo.push_branch_updates(remotes, &rebased_branch_updates)?;
         close_resolved_pull_requests(context, mirror_repo, remotes, repos, &rebased_branch_names)?;
     }
+    if !force_push_updates.is_empty() {
+        print_branch_force_pushes(&force_pushes);
+        backup_force_pushed_branches(context, mirror_repo, repo_name, &force_pushes, current_refs)?;
+        mirror_repo.push_branch_updates(remotes, &force_push_updates)?;
+        close_resolved_pull_requests(
+            context,
+            mirror_repo,
+            remotes,
+            repos,
+            &force_pushed_branch_names,
+        )?;
+    }
     if !tags_to_push.is_empty() {
         print_tag_decisions(&tags_to_push);
         mirror_repo.push_tags(remotes, &tags_to_push)?;
@@ -1541,10 +1582,14 @@ fn push_repo_refs(
     Ok(RepoRefSyncResult {
         pushed: !branches_to_push.is_empty()
             || !rebased_branch_updates.is_empty()
+            || !force_push_updates.is_empty()
             || !tags_to_push.is_empty()
             || !branch_deletions.is_empty()
             || !cleanup_branches.is_empty(),
-        had_conflicts: had_branch_conflicts || had_tag_conflicts || had_deletion_conflicts,
+        had_conflicts: had_branch_conflicts
+            || had_tag_conflicts
+            || had_deletion_conflicts
+            || had_force_push_conflicts,
     })
 }
 
@@ -1576,6 +1621,34 @@ fn backup_deleted_branches(
     Ok(())
 }
 
+fn backup_force_pushed_branches(
+    context: &RepoSyncContext<'_>,
+    mirror_repo: &GitMirror,
+    repo_name: &str,
+    force_pushes: &[BranchForcePush],
+    current_refs: &BTreeMap<String, RemoteRefState>,
+) -> Result<()> {
+    if context.dry_run {
+        crate::logln!(
+            "  {} {} force-push backup{}",
+            style("dry-run").yellow().bold(),
+            style("would create").dim(),
+            if force_pushes.len() == 1 { "" } else { "s" }
+        );
+        return Ok(());
+    }
+
+    let stamp = backup_stamp()?;
+    let backups = force_push_ref_backups(force_pushes, current_refs, &stamp);
+    if backups.is_empty() {
+        bail!("cannot back up force-push because no target branch refs were available");
+    }
+    let refs = mirror_repo.backup_refs(&backups)?;
+    let bundle_path = backup_dir(context, repo_name).join(format!("force-push-{stamp}.bundle"));
+    mirror_repo.create_bundle(&bundle_path, &refs)?;
+    Ok(())
+}
+
 fn backup_branches_deleted_everywhere(
     context: &RepoSyncContext<'_>,
     mirror_repo: &GitMirror,
@@ -1698,6 +1771,35 @@ fn log_rebase_decision(branch: &str, sha: &str, updates: &[BranchUpdate]) {
     );
 }
 
+fn print_branch_force_pushes(force_pushes: &[BranchForcePush]) {
+    for force_push in force_pushes {
+        crate::logln!(
+            "  {} branch {} {} -> {}",
+            style("force-push detected").green().bold(),
+            style(&force_push.branch).cyan(),
+            force_push.source_remotes.join("+"),
+            force_push.target_remotes.join("+")
+        );
+    }
+}
+
+fn force_push_updates(force_pushes: &[BranchForcePush]) -> Vec<BranchUpdate> {
+    force_pushes
+        .iter()
+        .flat_map(|force_push| {
+            force_push
+                .target_remotes
+                .iter()
+                .map(|target_remote| BranchUpdate {
+                    branch: force_push.branch.clone(),
+                    sha: force_push.sha.clone(),
+                    target_remote: target_remote.clone(),
+                    force: true,
+                })
+        })
+        .collect()
+}
+
 fn open_conflict_pull_requests(
     context: &RepoSyncContext<'_>,
     mirror_repo: &GitMirror,
@@ -1968,6 +2070,38 @@ fn branch_ref_backups(
     backups
 }
 
+fn force_push_ref_backups(
+    force_pushes: &[BranchForcePush],
+    current_refs: &BTreeMap<String, RemoteRefState>,
+    stamp: &str,
+) -> Vec<RefBackup> {
+    let mut backups = Vec::new();
+    for force_push in force_pushes {
+        for remote in &force_push.target_remotes {
+            let Some(sha) = current_refs
+                .get(remote)
+                .and_then(|refs| refs.branches.get(&force_push.branch))
+            else {
+                continue;
+            };
+            backups.push(RefBackup {
+                refname: format!(
+                    "refs/refray-backups/force-pushes/{}/{}/{}",
+                    hex_component(&force_push.branch),
+                    stamp,
+                    hex_component(remote)
+                ),
+                sha: sha.clone(),
+                description: format!(
+                    "branch {} from {} before propagated force-push",
+                    force_push.branch, remote
+                ),
+            });
+        }
+    }
+    backups
+}
+
 fn branches_deleted_everywhere_backups(
     previous_refs: &BTreeMap<String, RemoteRefState>,
     current_refs: &BTreeMap<String, RemoteRefState>,
@@ -2094,6 +2228,146 @@ fn safe_ref_component(value: &str) -> String {
     output.trim_matches('-').to_string()
 }
 
+#[derive(Clone, Debug)]
+struct BranchForcePush {
+    branch: String,
+    sha: String,
+    source_remotes: Vec<String>,
+    target_remotes: Vec<String>,
+}
+
+struct BranchForcePushConflict {
+    branch: String,
+    remotes: Vec<String>,
+    reason: String,
+}
+
+fn branch_force_push_decisions(
+    mirror_repo: &GitMirror,
+    remotes: &[RemoteSpec],
+    previous_refs: Option<&BTreeMap<String, RemoteRefState>>,
+    current_refs: &BTreeMap<String, RemoteRefState>,
+) -> Result<(
+    Vec<BranchForcePush>,
+    Vec<BranchForcePushConflict>,
+    BTreeSet<String>,
+)> {
+    let Some(previous_refs) = previous_refs else {
+        return Ok((Vec::new(), Vec::new(), BTreeSet::new()));
+    };
+    let remote_names = remotes
+        .iter()
+        .map(|remote| remote.name.clone())
+        .collect::<Vec<_>>();
+    let mut branches = BTreeSet::new();
+    for refs in previous_refs.values() {
+        branches.extend(
+            refs.branches
+                .keys()
+                .filter(|branch| !is_internal_conflict_branch(branch))
+                .cloned(),
+        );
+    }
+
+    let mut decisions = Vec::new();
+    let mut conflicts = Vec::new();
+    let mut blocked = BTreeSet::new();
+    for branch in branches {
+        let previous_by_remote = remote_names
+            .iter()
+            .filter_map(|remote| {
+                previous_refs
+                    .get(remote)
+                    .and_then(|refs| refs.branches.get(&branch))
+                    .map(|sha| (remote.clone(), sha.clone()))
+            })
+            .collect::<BTreeMap<_, _>>();
+        if previous_by_remote.len() != remote_names.len() {
+            continue;
+        }
+        let previous_tips = previous_by_remote
+            .values()
+            .cloned()
+            .collect::<BTreeSet<_>>();
+        if previous_tips.len() != 1 {
+            continue;
+        }
+
+        let current_by_remote = remote_names
+            .iter()
+            .filter_map(|remote| {
+                current_refs
+                    .get(remote)
+                    .and_then(|refs| refs.branches.get(&branch))
+                    .map(|sha| (remote.clone(), sha.clone()))
+            })
+            .collect::<BTreeMap<_, _>>();
+        if current_by_remote.len() != remote_names.len() {
+            continue;
+        }
+
+        let mut target_remotes = Vec::new();
+        let mut fast_forward_remotes = Vec::new();
+        let mut force_pushed_by_tip = BTreeMap::<String, Vec<String>>::new();
+        for remote in &remote_names {
+            let previous = &previous_by_remote[remote];
+            let current = &current_by_remote[remote];
+            if previous == current {
+                target_remotes.push(remote.clone());
+            } else if mirror_repo.is_ancestor(previous, current)? {
+                fast_forward_remotes.push(remote.clone());
+            } else {
+                force_pushed_by_tip
+                    .entry(current.clone())
+                    .or_default()
+                    .push(remote.clone());
+            }
+        }
+
+        if force_pushed_by_tip.is_empty() {
+            continue;
+        }
+
+        let force_pushed_remotes = force_pushed_by_tip
+            .values()
+            .flat_map(|remotes| remotes.iter().cloned())
+            .collect::<Vec<_>>();
+        if force_pushed_by_tip.len() == 1 && fast_forward_remotes.is_empty() {
+            let (sha, source_remotes) = force_pushed_by_tip.into_iter().next().unwrap();
+            if target_remotes.is_empty() {
+                continue;
+            }
+            blocked.insert(branch.clone());
+            decisions.push(BranchForcePush {
+                branch,
+                sha,
+                source_remotes,
+                target_remotes,
+            });
+            continue;
+        }
+
+        blocked.insert(branch.clone());
+        let reason = if force_pushed_by_tip.len() > 1 && !fast_forward_remotes.is_empty() {
+            format!(
+                "multiple rewritten tips and fast-forward changes on {}",
+                fast_forward_remotes.join("+")
+            )
+        } else if force_pushed_by_tip.len() > 1 {
+            "multiple rewritten tips".to_string()
+        } else {
+            format!("also fast-forwarded on {}", fast_forward_remotes.join("+"))
+        };
+        conflicts.push(BranchForcePushConflict {
+            branch,
+            remotes: force_pushed_remotes,
+            reason,
+        });
+    }
+
+    Ok((decisions, conflicts, blocked))
+}
+
 struct BranchDeletionConflict {
     branch: String,
     deleted_remotes: Vec<String>,

tests/e2e/sequential.rs

@@ -25,8 +25,7 @@ const WEBHOOK_SECRET: &str = "refray-e2e-secret";
 #[test]
 #[ignore = "destructive live-provider e2e test; run explicitly with --ignored"]
 fn sequential_live_e2e_all_supported_features() -> Result<()> {
-    let env = EnvFile::load(Path::new(".env"))?;
-    let settings = E2eSettings::from_env(&env)?;
+    let settings = load_e2e_settings()?;
     settings.require_destructive_guard()?;
 
     let mut run = E2eRun::new(settings)?;
@@ -59,6 +58,42 @@ fn sequential_live_e2e_all_supported_features() -> Result<()> {
     Ok(())
 }
 
+#[test]
+#[ignore = "destructive live-provider e2e test; run explicitly with --ignored"]
+fn sequential_live_e2e_force_push_detection() -> Result<()> {
+    let settings = load_e2e_settings()?;
+    settings.require_destructive_guard()?;
+
+    let mut run = E2eRun::new(settings)?;
+    run.preflight()?;
+    run.clear_repositories()?;
+    run.write_config(ConflictMode::AutoRebasePullRequest, None, true)?;
+
+    eprintln!("e2e phase: force-push rewind");
+    run.rewind_force_push_propagates()?;
+    eprintln!("e2e phase: force-push rewrite");
+    run.rewrite_force_push_propagates()?;
+    eprintln!("e2e phase: force-push fast-forward guard");
+    run.normal_fast_forward_still_syncs()?;
+    eprintln!("e2e phase: force-push conflict");
+    run.conflicting_force_pushes_are_not_propagated()?;
+    eprintln!("e2e phase: force-push plus fast-forward conflict");
+    run.force_push_plus_fast_forward_is_not_propagated()?;
+    eprintln!("e2e phase: feature branch force-push");
+    run.feature_branch_force_push_propagates()?;
+
+    run.clear_e2e_repositories()?;
+    Ok(())
+}
+
+fn load_e2e_settings() -> Result<E2eSettings> {
+    let env_path = std::env::var_os("REFRAY_E2E_ENV_FILE")
+        .map(PathBuf::from)
+        .unwrap_or_else(|| PathBuf::from(".env"));
+    let env = EnvFile::load(&env_path)?;
+    E2eSettings::from_env(&env)
+}
+
 struct EnvFile {
     values: HashMap<String, String>,
 }
@@ -637,6 +672,218 @@ namespace = "{}"
         Ok(())
     }
 
+    fn rewind_force_push_propagates(&self) -> Result<()> {
+        let repo = self.repo_name("force-rewind");
+        let source = self.primary_provider();
+        self.seed_all_main(&repo, "force rewind base", 1_700_001_701)?;
+        self.sync_repo(&repo, [])?;
+        let base = self.branch_sha(source, &repo, MAIN_BRANCH)?;
+        let old = self.commit_to_provider_branch(
+            source,
+            &repo,
+            MAIN_BRANCH,
+            "old.txt",
+            "old\n",
+            "force rewind old",
+            1_700_001_702,
+        )?;
+        self.sync_repo(&repo, [])?;
+        self.assert_branch_all_at(&repo, MAIN_BRANCH, &old)?;
+        self.unprotect_main_all(&repo)?;
+
+        self.force_push_provider_branch_to_sha(source, &repo, MAIN_BRANCH, &base)?;
+        self.sync_repo(&repo, [])?;
+        self.assert_branch_all_at(&repo, MAIN_BRANCH, &base)?;
+        self.assert_backup_bundle_contains(&repo, &old)?;
+        Ok(())
+    }
+
+    fn rewrite_force_push_propagates(&self) -> Result<()> {
+        let repo = self.repo_name("force-rewrite");
+        let source = self.primary_provider();
+        self.seed_all_main(&repo, "force rewrite base", 1_700_001_711)?;
+        self.sync_repo(&repo, [])?;
+        let base = self.branch_sha(source, &repo, MAIN_BRANCH)?;
+        let old = self.commit_to_provider_branch(
+            source,
+            &repo,
+            MAIN_BRANCH,
+            "old.txt",
+            "old\n",
+            "force rewrite old",
+            1_700_001_712,
+        )?;
+        self.sync_repo(&repo, [])?;
+        self.assert_branch_all_at(&repo, MAIN_BRANCH, &old)?;
+        self.unprotect_main_all(&repo)?;
+
+        let rewritten = self.force_rewrite_provider_branch_from(
+            source,
+            &repo,
+            MAIN_BRANCH,
+            &base,
+            "rewritten.txt",
+            "rewritten\n",
+            "force rewrite new",
+            1_700_001_713,
+        )?;
+        self.sync_repo(&repo, [])?;
+        self.assert_branch_all_at(&repo, MAIN_BRANCH, &rewritten)?;
+        self.assert_backup_bundle_contains(&repo, &old)?;
+        Ok(())
+    }
+
+    fn normal_fast_forward_still_syncs(&self) -> Result<()> {
+        let repo = self.repo_name("force-fast-forward");
+        let source = self.primary_provider();
+        self.seed_all_main(&repo, "force fast-forward base", 1_700_001_721)?;
+        self.sync_repo(&repo, [])?;
+
+        let newer = self.commit_to_provider_branch(
+            source,
+            &repo,
+            MAIN_BRANCH,
+            "newer.txt",
+            "newer\n",
+            "normal fast-forward",
+            1_700_001_722,
+        )?;
+        self.sync_repo(&repo, [])?;
+        self.assert_branch_all_at(&repo, MAIN_BRANCH, &newer)
+    }
+
+    fn conflicting_force_pushes_are_not_propagated(&self) -> Result<()> {
+        let repo = self.repo_name("force-conflict");
+        let (source, peer) = self.provider_pair();
+        self.seed_all_main(&repo, "force conflict base", 1_700_001_731)?;
+        self.sync_repo(&repo, [])?;
+        let base = self.branch_sha(source, &repo, MAIN_BRANCH)?;
+        let old = self.commit_to_provider_branch(
+            source,
+            &repo,
+            MAIN_BRANCH,
+            "old.txt",
+            "old\n",
+            "force conflict old",
+            1_700_001_732,
+        )?;
+        self.sync_repo(&repo, [])?;
+        self.assert_branch_all_at(&repo, MAIN_BRANCH, &old)?;
+        self.unprotect_main_all(&repo)?;
+
+        self.force_rewrite_provider_branch_from(
+            source,
+            &repo,
+            MAIN_BRANCH,
+            &base,
+            "source.txt",
+            "source\n",
+            "source force rewrite",
+            1_700_001_733,
+        )?;
+        self.force_rewrite_provider_branch_from(
+            peer,
+            &repo,
+            MAIN_BRANCH,
+            &base,
+            "peer.txt",
+            "peer\n",
+            "peer force rewrite",
+            1_700_001_734,
+        )?;
+        let expected_refs = self.branch_refs_by_provider(&repo, MAIN_BRANCH)?;
+
+        self.write_config(ConflictMode::Fail, Some(&exact_pattern(&repo)), true)?;
+        self.sync_repo_expect_failure(&repo, [])?;
+        self.assert_branch_refs_match(&repo, MAIN_BRANCH, &expected_refs)?;
+        self.write_config(ConflictMode::AutoRebasePullRequest, None, true)?;
+        Ok(())
+    }
+
+    fn force_push_plus_fast_forward_is_not_propagated(&self) -> Result<()> {
+        let repo = self.repo_name("force-plus-fast-forward");
+        let (source, peer) = self.provider_pair();
+        self.seed_all_main(&repo, "force plus fast-forward base", 1_700_001_741)?;
+        self.sync_repo(&repo, [])?;
+        let base = self.branch_sha(source, &repo, MAIN_BRANCH)?;
+        let old = self.commit_to_provider_branch(
+            source,
+            &repo,
+            MAIN_BRANCH,
+            "old.txt",
+            "old\n",
+            "force plus fast-forward old",
+            1_700_001_742,
+        )?;
+        self.sync_repo(&repo, [])?;
+        self.assert_branch_all_at(&repo, MAIN_BRANCH, &old)?;
+        self.unprotect_main_all(&repo)?;
+
+        self.force_rewrite_provider_branch_from(
+            source,
+            &repo,
+            MAIN_BRANCH,
+            &base,
+            "rewritten.txt",
+            "rewritten\n",
+            "force plus fast-forward rewrite",
+            1_700_001_743,
+        )?;
+        self.commit_to_provider_branch(
+            peer,
+            &repo,
+            MAIN_BRANCH,
+            "peer-fast-forward.txt",
+            "peer fast-forward\n",
+            "peer fast-forward",
+            1_700_001_744,
+        )?;
+        let expected_refs = self.branch_refs_by_provider(&repo, MAIN_BRANCH)?;
+
+        self.write_config(ConflictMode::Fail, Some(&exact_pattern(&repo)), true)?;
+        self.sync_repo_expect_failure(&repo, [])?;
+        self.assert_branch_refs_match(&repo, MAIN_BRANCH, &expected_refs)?;
+        self.write_config(ConflictMode::AutoRebasePullRequest, None, true)?;
+        Ok(())
+    }
+
+    fn feature_branch_force_push_propagates(&self) -> Result<()> {
+        let repo = self.repo_name("force-feature");
+        let source = self.primary_provider();
+        let branch = "feature/force-push";
+        self.seed_all_main(&repo, "force feature base", 1_700_001_751)?;
+        self.sync_repo(&repo, [])?;
+        let main = self.branch_sha(source, &repo, MAIN_BRANCH)?;
+        let old_feature = self.create_provider_branch(
+            source,
+            &repo,
+            MAIN_BRANCH,
+            branch,
+            "feature.txt",
+            "feature\n",
+            "feature branch old",
+            1_700_001_752,
+        )?;
+        self.sync_repo(&repo, [])?;
+        self.assert_branch_all_at(&repo, branch, &old_feature)?;
+
+        let rewritten_feature = self.force_rewrite_provider_branch_from(
+            source,
+            &repo,
+            branch,
+            &main,
+            "feature-rewritten.txt",
+            "feature rewritten\n",
+            "feature branch rewrite",
+            1_700_001_753,
+        )?;
+        self.sync_repo(&repo, [])?;
+        self.assert_branch_all_at(&repo, branch, &rewritten_feature)?;
+        self.assert_branch_all_at(&repo, MAIN_BRANCH, &main)?;
+        self.assert_backup_bundle_contains(&repo, &old_feature)?;
+        Ok(())
+    }
+
     fn webhook_commands_and_receiver_work(&self) -> Result<()> {
         let repo = self.repo_name("webhook");
         let source = self.primary_provider();
@@ -765,6 +1012,129 @@ namespace = "{}"
         Ok(())
     }
 
+    #[allow(clippy::too_many_arguments)]
+    fn commit_to_provider_branch(
+        &self,
+        provider: &ProviderAccount,
+        repo: &str,
+        branch: &str,
+        path: &str,
+        contents: &str,
+        message: &str,
+        timestamp: i64,
+    ) -> Result<String> {
+        let work = self.clone_repo(
+            provider,
+            repo,
+            &format!(
+                "commit-{}-{}-{repo}",
+                provider.site_name,
+                sanitize_path(branch)
+            ),
+        )?;
+        self.checkout_remote_branch(&work, branch)?;
+        write_commit(&work, path, contents, message, timestamp)?;
+        let sha = git_output(&work, ["rev-parse", "HEAD"])?;
+        let refspec = format!("HEAD:{branch}");
+        self.git(&work, ["push", "origin", &refspec])?;
+        provider.wait_branch(repo, branch, &sha)?;
+        provider.wait_repo_listed(repo)?;
+        Ok(sha)
+    }
+
+    #[allow(clippy::too_many_arguments)]
+    fn create_provider_branch(
+        &self,
+        provider: &ProviderAccount,
+        repo: &str,
+        base_branch: &str,
+        branch: &str,
+        path: &str,
+        contents: &str,
+        message: &str,
+        timestamp: i64,
+    ) -> Result<String> {
+        let work = self.clone_repo(
+            provider,
+            repo,
+            &format!(
+                "branch-{}-{}-{repo}",
+                provider.site_name,
+                sanitize_path(branch)
+            ),
+        )?;
+        let base_ref = format!("origin/{base_branch}");
+        self.git(&work, ["checkout", "-B", branch, &base_ref])?;
+        write_commit(&work, path, contents, message, timestamp)?;
+        let sha = git_output(&work, ["rev-parse", "HEAD"])?;
+        let refspec = format!("HEAD:{branch}");
+        self.git(&work, ["push", "origin", &refspec])?;
+        provider.wait_branch(repo, branch, &sha)?;
+        provider.wait_repo_listed(repo)?;
+        Ok(sha)
+    }
+
+    fn force_push_provider_branch_to_sha(
+        &self,
+        provider: &ProviderAccount,
+        repo: &str,
+        branch: &str,
+        sha: &str,
+    ) -> Result<()> {
+        let work = self.clone_repo(
+            provider,
+            repo,
+            &format!(
+                "force-to-{}-{}-{repo}",
+                provider.site_name,
+                sanitize_path(branch)
+            ),
+        )?;
+        self.checkout_remote_branch(&work, branch)?;
+        self.git(&work, ["reset", "--hard", sha])?;
+        let refspec = format!("HEAD:{branch}");
+        self.git(&work, ["push", "--force", "origin", &refspec])?;
+        provider.wait_branch(repo, branch, sha)?;
+        provider.wait_repo_listed(repo)
+    }
+
+    #[allow(clippy::too_many_arguments)]
+    fn force_rewrite_provider_branch_from(
+        &self,
+        provider: &ProviderAccount,
+        repo: &str,
+        branch: &str,
+        base_sha: &str,
+        path: &str,
+        contents: &str,
+        message: &str,
+        timestamp: i64,
+    ) -> Result<String> {
+        let work = self.clone_repo(
+            provider,
+            repo,
+            &format!(
+                "force-rewrite-{}-{}-{repo}",
+                provider.site_name,
+                sanitize_path(branch)
+            ),
+        )?;
+        self.checkout_remote_branch(&work, branch)?;
+        self.git(&work, ["reset", "--hard", base_sha])?;
+        write_commit(&work, path, contents, message, timestamp)?;
+        let sha = git_output(&work, ["rev-parse", "HEAD"])?;
+        let refspec = format!("HEAD:{branch}");
+        self.git(&work, ["push", "--force", "origin", &refspec])?;
+        provider.wait_branch(repo, branch, &sha)?;
+        provider.wait_repo_listed(repo)?;
+        Ok(sha)
+    }
+
+    fn checkout_remote_branch(&self, work: &Path, branch: &str) -> Result<()> {
+        let remote_branch = format!("origin/{branch}");
+        self.git(work, ["checkout", "-B", branch, &remote_branch])
+    }
+
     fn clone_repo(&self, provider: &ProviderAccount, repo: &str, label: &str) -> Result<PathBuf> {
         let path = self.git_worktree(label)?;
         let remote_url = provider.authenticated_repo_url(repo)?;
@@ -1058,6 +1428,34 @@ namespace = "{}"
         })
     }
 
+    fn assert_branch_all_at(&self, repo: &str, branch: &str, expected: &str) -> Result<()> {
+        retry("branch convergence to expected tip", || {
+            for (provider, actual) in self.branch_refs_by_provider(repo, branch)? {
+                if actual != expected {
+                    bail!("branch {branch} on {provider} is at {actual}, expected {expected}");
+                }
+            }
+            Ok(())
+        })
+    }
+
+    fn assert_branch_refs_match(
+        &self,
+        repo: &str,
+        branch: &str,
+        expected: &BTreeMap<String, String>,
+    ) -> Result<()> {
+        retry("branch refs unchanged", || {
+            let actual = self.branch_refs_by_provider(repo, branch)?;
+            if &actual != expected {
+                bail!(
+                    "branch {branch} refs changed unexpectedly for {repo}: expected {expected:?}, got {actual:?}"
+                );
+            }
+            Ok(())
+        })
+    }
+
     fn assert_branch_all_equal_after_optional_resync(
         &self,
         repo: &str,
@@ -1224,6 +1622,36 @@ namespace = "{}"
         Ok(output)
     }
 
+    fn branch_refs_by_provider(
+        &self,
+        repo: &str,
+        branch: &str,
+    ) -> Result<BTreeMap<String, String>> {
+        let mut output = BTreeMap::new();
+        for (provider, refs) in self.refs_by_provider(repo)? {
+            let sha =
+                refs.branches.get(branch).cloned().ok_or_else(|| {
+                    anyhow!("branch {branch} missing on {provider} for repo {repo}")
+                })?;
+            output.insert(provider, sha);
+        }
+        Ok(output)
+    }
+
+    fn branch_sha(&self, provider: &ProviderAccount, repo: &str, branch: &str) -> Result<String> {
+        provider
+            .ls_remote(repo)?
+            .branches
+            .get(branch)
+            .cloned()
+            .ok_or_else(|| {
+                anyhow!(
+                    "branch {branch} missing on {} for repo {repo}",
+                    provider.site_name
+                )
+            })
+    }
+
     fn unprotect_main_all(&self, repo: &str) -> Result<()> {
         for provider in &self.settings.providers {
             provider.unprotect_branch(repo, MAIN_BRANCH)?;

tests/unit/git.rs

@@ -178,7 +178,15 @@ fn auto_rebase_branch_conflict_replays_later_tip_and_marks_force_targets() {
     let a_tip = fixture.commit_file("a", "a.txt", "a\n", 1_700_000_100);
     fixture.push_head(&fixture.remote_a, "main");
     fixture.reset_hard(&base);
-    let b_tip = fixture.commit_file("b", "b.txt", "b\n", 1_700_000_200);
+    let b_tip = fixture.commit_file_with_committer(
+        "b",
+        "b.txt",
+        "b\n",
+        1_700_000_200,
+        "Original Committer",
+        "original-committer@example.test",
+        1_700_000_250,
+    );
     fixture.push_head(&fixture.remote_b, "main");
 
     let mirror = fixture.mirror();
@@ -205,6 +213,10 @@ fn auto_rebase_branch_conflict_replays_later_tip_and_marks_force_targets() {
         .find(|update| update.target_remote == "b")
         .unwrap();
     assert!(b_update.force);
+    assert_eq!(
+        fixture.mirror_committer(&decision.sha),
+        fixture.mirror_committer(&b_tip)
+    );
 
     mirror
         .push_branch_updates(&fixture.remotes(), &decision.updates)
@@ -495,6 +507,35 @@ impl GitFixture {
         self.head()
     }
 
+    fn commit_file_with_committer(
+        &self,
+        message: &str,
+        file_name: &str,
+        contents: &str,
+        author_timestamp: i64,
+        committer_name: &str,
+        committer_email: &str,
+        committer_timestamp: i64,
+    ) -> String {
+        let path = self.work.join(file_name);
+        fs::write(path, contents).unwrap();
+        git(Some(&self.work), ["add", file_name]);
+
+        let author_date = format!("@{author_timestamp} +0000");
+        let committer_date = format!("@{committer_timestamp} +0000");
+        let output = Command::new("git")
+            .current_dir(&self.work)
+            .env("GIT_AUTHOR_DATE", &author_date)
+            .env("GIT_COMMITTER_NAME", committer_name)
+            .env("GIT_COMMITTER_EMAIL", committer_email)
+            .env("GIT_COMMITTER_DATE", &committer_date)
+            .args(["commit", "-m", message])
+            .output()
+            .unwrap();
+        assert_success(&output, "git commit");
+        self.head()
+    }
+
     fn head(&self) -> String {
         git_output(Some(&self.work), ["rev-parse", "HEAD"])
     }
@@ -559,6 +600,20 @@ impl GitFixture {
         .status
         .success()
     }
+
+    fn mirror_committer(&self, reference: &str) -> String {
+        git_output(
+            None,
+            [
+                "--git-dir",
+                self.mirror_path.to_str().unwrap(),
+                "show",
+                "-s",
+                "--format=%cn <%ce> %cI",
+                reference,
+            ],
+        )
+    }
 }
 
 fn git<const N: usize>(current_dir: Option<&Path>, args: [&str; N]) {