# checkpoint resume: simplify picker and prefix gate

`c6659c5`→[main](/content/gh/entireio/cli/commits/main/index.html)·

Rely on store.List's documented newest-first ordering instead of re-sorting, move the checkpoint-prefix shape gate into the id package next to the patterns it must not drift from, reuse the existing picker cancel sentinel, and share the repeated test repo setup.

## Sessions

01KX48VMKTYXYNTAGAK3B2BCQNView transcript

## Changes

4

- cmd/entire/cli

- checkpoint/id

- Mid.go+14

- Mid_test.go+24

- Mcheckpoint_resume.go+11/-26

- Mcheckpoint_resume_test.go+15/-48

```go
43 unmodified lines

// a loose shape, not authoritative validation).
const CheckpointPattern = `(?:` + Pattern + `|` + ulidPattern + `)`

// prefixShapeRegex matches strings shaped like a checkpoint ID or a prefix of
// one: 1-12 lowercase hex characters (legacy) or 1-26 Crockford base32
// characters (ULID). Kept next to Pattern/ulidPattern so the alphabet and
// width bounds cannot drift from the full-ID patterns above.
var prefixShapeRegex = regexp.MustCompile(`^(?:[0-9a-f]{1,12}|[0-9ABCDEFGHJKMNPQRSTVWXYZ]{1,26})$`)

// CouldBePrefix reports whether s is shaped like a checkpoint ID or a prefix
// of one. It is a cheap gate for callers deciding whether a free-form target
// could name a checkpoint before paying for a store lookup; it is not
// validation (see Validate).
func CouldBePrefix(s string) bool {
	return prefixShapeRegex.MatchString(s)
}

// ShortIDLength is the standard length for truncating IDs for display purposes.
// Used for tool use IDs, session IDs, and commit hashes in logs and messages.
const ShortIDLength = 12
```

```go
func TestCouldBePrefix(t *testing.T) {
	t.Parallel()
	tests := []struct {
		input string
		want  bool
	}{
		{"abc123", true},
		{"abc123def456", true},
		{"01HZXW5J8KQ2M3N4P5Q6R7S8T9", true},
		{"01HZXW", true},
		{"HEAD", true},
		{"", false},
		{"abc123def4567", false},
		{"feature/foo", false},
		{"abcdefI", false},
		{"01hzxw5j8kq2m3n4p5q6r7s8t9x", false},
	}
	for _, tt := range tests {
		if got := CouldBePrefix(tt.input); got != tt.want {
			t.Errorf("CouldBePrefix(%q) = %v, want %v", tt.input, got, tt.want)
		}
	}
}
```

```go
func TestRecentCheckpoints_SortsNewestFirstAndCaps(t *testing.T) {
	t.Parallel()
	base := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
	var infos []checkpoint.CheckpointInfo
	for i := range 25 {
		infos = append(infos, checkpoint.CheckpointInfo{
			CheckpointID: id.MustCheckpointID(fmt.Sprintf("%012x", i)),
			CreatedAt:    base.Add(time.Duration(i) * time.Hour),
		})
	}
	got := recentCheckpoints(infos, 20)
	if len(got) != 20 {
		t.Fatalf("len = %d, want 20", len(got))
	}
	if !got[0].CreatedAt.After(got[19].CreatedAt) {
		t.Errorf("not sorted newest first: got[0]=%v got[19]=%v", got[0].CreatedAt, got[19].CreatedAt)
	}
	if got[0].CreatedAt != base.Add(24*time.Hour) {
		t.Errorf("newest = %v, want %v", got[0].CreatedAt, base.Add(24*time.Hour))
	}
}
```

Jaeger's test repo setup for various test cases involving checkpoints and their management is also studied thoroughly.