test(s3/lifecycle): integration coverage for empty bucket sweep no-op

A bucket carrying lifecycle config but no objects must produce a
successful sweep — no hangs, no errors, no dispatches. Pinned
because the bootstrap walker iterates bucket directories, and an
empty directory is a corner of that traversal that's easy to break
(slice-bounds bug on the first listing returning zero entries).

Asserts: worker logs "loaded lifecycle for" and "shards 0-15
complete", no FATAL output, bucket still exists after the sweep.

test/s3/lifecycle/s3_lifecycle_empty_bucket_test.go

@@ -0,0 +1,46 @@
+// Empty bucket sweep — no-op safety integration scenario.
+package lifecycle
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/aws"
+	"github.com/aws/aws-sdk-go-v2/service/s3"
+	"github.com/stretchr/testify/require"
+)
+
+// TestLifecycleEmptyBucketSweepIsNoOp: a bucket carrying lifecycle
+// config but no objects must produce a successful sweep — no hangs,
+// no errors, no dispatches. Pinned because the bootstrap walker
+// iterates bucket directories, and an empty directory is a corner of
+// that traversal that's easy to break (e.g. a slice-bounds bug on
+// the first listing returning zero entries).
+func TestLifecycleEmptyBucketSweepIsNoOp(t *testing.T) {
+	c := s3Client(t)
+	_, fcClose := filerClient(t)
+	defer fcClose()
+
+	bucket := uniqueBucket("empty")
+	mustCreateBucket(t, c, bucket)
+	putExpirationLifecycle(t, c, bucket, "anywhere/", 1)
+
+	// No PUTs. The bucket is empty.
+
+	out := runLifecycleShard(t)
+	t.Logf("sweep output:\n%s", out)
+
+	// Sanity: the worker must report it loaded the bucket's config and
+	// completed without errors. The runLifecycleShard helper already
+	// fails on FATAL; pin the success markers here too so a regression
+	// that produces a half-shaped output (no completion) is caught.
+	require.Contains(t, out, "loaded lifecycle for", "worker must report config load")
+	require.Contains(t, out, "shards 0-15 complete", "worker must complete all shards")
+	require.False(t, strings.Contains(out, "FATAL"), "worker must not produce FATAL output")
+
+	// Bucket still exists after the sweep — the worker doesn't drop
+	// empty buckets as a side effect.
+	_, err := c.HeadBucket(context.Background(), &s3.HeadBucketInput{Bucket: aws.String(bucket)})
+	require.NoError(t, err, "empty bucket must still exist after sweep")
+}