# Merge pull request #86 from entireio/fix/already-exists-create-race

`4991b7b`→[main](/content/gh/entireio/git-sync/commits/main/index.html)·

nodo·1mo ago·3 files·+27 added/-3 removed

gitproto: classify create-side CAS races (already exists) as ErrTargetRefMoved

## Changes

3

- MCHANGELOG.md+6

- internal/gitproto

- Mpush.go+17/-3

- Mpush_test.go+4

```
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The format is based on [Keep a Changelog](https://keepachangelog.com/),
and this project adheres to [Semantic Versioning](https://semver.org/).

## [Unreleased]

### Fixed

- Concurrent **create** races on the target are now classified as `ErrTargetRefMoved`, matching the existing concurrent-update handling. entire-server rejects a create command (old = zero hash) for a ref that already exists with `already exists`; git-sync only plans a create for a ref it found absent at plan time, so that rejection is an unambiguous benign race — a second sync of the same repo created the ref first — exactly like the update-side `remote ref has changed`. Previously only the update reason was in `concurrentMoveMarkers`, so a create race fell through as a generic push failure and `errors.Is(err, ErrTargetRefMoved)` returned false; embedders that key redelivery/alerting off the sentinel (e.g. mirror-pipeline's worker) misclassified it as a hard sync failure. Both the create and update CAS rejections now satisfy `errors.Is(err, ErrTargetRefMoved)`.

## [0.7.0] - 2026-06-16

### Added
```

MCHANGELOG.md+6

```

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// concurrentMoveMarkers are receive-pack ng reasons that UNAMBIGUOUSLY mean the
// target ref changed under us between plan and push — a clean compare-and-swap /
// lease miss that a plain retry resolves. Deliberately NARROWER than
// lease miss that a plain retry resolves. "Changed" covers both an existing ref
// moving to a new tip AND a planned-absent ref appearing: each is a concurrent
// push of the same repo winning the race, and each self-heals on the next run
// (re-plan against the new state usually no-ops). Deliberately NARROWER than
// leaseFailureMarkers: "non-fast-forward" / "fetch first" are excluded because an
// update that is legitimately non-fast-forward and wasn't force-pushed looks
// identical to a race, and treating it as a benign move would mask a real
// "needs --force" failure.
//
// This set is server-specific by design. "remote ref has changed" is
// entire-server's compare-and-swap rejection (storage.ErrReferenceHasChanged) —
// the one git-sync's own targets emit, and the case that matters in practice.
// entire-server's update-side compare-and-swap rejection
// (storage.ErrReferenceHasChanged): the planned old hash no longer matches the
// target tip. "already exists" is the same CAS on the create side — git-sync
// only emits a create command (old = zero hash) for a ref it found ABSENT at
// plan time, so the server reporting it present at push time can only mean a
// concurrent sync created it first. That makes "already exists" exactly as
// unambiguous a race as "remote ref has changed", just for the create rather
// than the update path; both are the rejections git-sync's own targets emit, and
// the cases that matter in practice. (entire-server's bootstrap-mode planner has
// a separate "target ref ... already exists" *planning* error, but that never
// reaches receive-pack report-status, so it can't surface here.)
//
// "stale info" is git's force-with-lease lease-miss phrasing, kept for
// consistency with leaseFailureMarkers and defence-in-depth; note it is
// primarily a client-side status, so it may not arrive as a server ng reason on
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// RefRejectedError).
var concurrentMoveMarkers = []string{
	"remote ref has changed",
	"already exists",
	"stale info",
}
```

Minternal/gitproto/push.go+17/-3

```

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}{
		{"entire-server CAS rejection", "remote ref has changed", true},
		{"CAS rejection with surrounding detail", "command error on refs/heads/main: remote ref has changed", true},
		{"entire-server create-side CAS rejection", "already exists", true},
		{"create-side CAS with surrounding detail", "command error on refs/heads/PIE-11736: already exists", true},
		{"already exists case-insensitive", "Already Exists", true},
		{"force-with-lease stale info", "stale info", true},
		{"stale info case-insensitive", "Stale Info", true},
		// Deliberately NOT moves: a plain non-fast-forward that wasn't force-pushed
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Moved  bool
	}{
		{"concurrent move (remote ref has changed)", "remote ref has changed", true},
		{"concurrent create (already exists)", "already exists", true},
		{"lease miss (stale info)", "stale info", true},
		{"ambiguous non-fast-forward is not a move", "non-fast-forward", false},
		{"policy rejection is not a move", "deny updating a hidden ref", false},