feat(s3/lifecycle): enable scheduler by default (#9492)

S3 lifecycle is a standard bucket feature — operators set
PutBucketLifecycleConfiguration through the S3 API expecting the
configured expirations to actually fire. With the prior default
(scheduler enabled=false), buckets with lifecycle XML silently
retained data past their declared expiration until an operator
noticed and turned the scheduler on.

The failure mode of enabled-by-default is "worker runs every day
and fast-exits on buckets with no lifecycle rules" — cheap.
The failure mode of disabled-by-default is "data lingers, looks
like it expired, doesn't" — bad. Enabled-by-default matches both
the AWS S3 default behavior and the operator's natural mental
model.

Operators who want the worker off can still disable it via the
admin UI; once a persisted config exists, this descriptor default
no longer applies (the persisted Enabled state wins).

Test pins the choice so a future flip to false fails loud.

weed/worker/tasks/s3_lifecycle/handler.go

@@ -143,6 +143,15 @@ func (h *Handler) Descriptor() *plugin_pb.JobTypeDescriptor {
 			},
 		},
 		AdminRuntimeDefaults: &plugin_pb.AdminRuntimeDefaults{
+			// On by default: S3 lifecycle is a standard bucket feature
+			// (PutBucketLifecycleConfiguration is part of the S3 API),
+			// and a bucket with rules set but no worker running silently
+			// retains data past its declared expiration. Operators who
+			// want the worker off can still disable it in the admin UI;
+			// the default error is "data lingers" not "worker burns CPU
+			// on empty rule sets" (the worker fast-exits with no
+			// configured rules).
+			Enabled:                  true,
 			DetectionIntervalMinutes: 24 * 60, // daily
 			DetectionTimeoutSeconds:  60,
 			MaxJobsPerDetection:      1,

weed/worker/tasks/s3_lifecycle/handler_test.go

@@ -348,6 +348,20 @@ func TestDescriptor_AdminRuntimeDefaultsDailyCadence(t *testing.T) {
 	assert.Equal(t, int32(1), d.AdminRuntimeDefaults.MaxJobsPerDetection)
 }
 
+func TestDescriptor_AdminRuntimeDefaultsEnabledByDefault(t *testing.T) {
+	// S3 lifecycle is a standard bucket feature — operators set
+	// PutBucketLifecycleConfiguration expecting it to actually fire.
+	// Default-off would silently retain data past declared expiration
+	// until an operator notices and flips it on. Document the choice
+	// here so a future change to disabled-by-default fails the test
+	// and surfaces a conscious revisit.
+	h := NewHandler(nil)
+	d := h.Descriptor()
+	require.NotNil(t, d.AdminRuntimeDefaults)
+	assert.True(t, d.AdminRuntimeDefaults.Enabled,
+		"s3_lifecycle defaults must enable the scheduler so configured rules fire without operator opt-in")
+}
+
 // ---------- Execute ----------
 
 // recordingExecSender captures Execute-side messages. The Execute path