test(s3/lifecycle): bundle reader + scheduler helper coverage (#9412)

* test(s3/lifecycle): bundle reader + scheduler helper coverage

Bundles direct tests for previously-uncovered helpers in two
packages. Bumps reader 73.2% → 79.2% and scheduler 71.6% → 73.6%.

Reader Event predicates (4):
- IsCreate: NewEntry-only event classifies as create
- IsDelete: OldEntry-only event classifies as delete
- both entries (update): neither IsCreate nor IsDelete (strict
  exclusivity so router routes updates through their own path)
- no entries (degenerate): neither (so a metadata-only filer event
  with no payload doesn't trigger spurious dispatches)

Reader LogStartup (4): exercises both shape branches (single-shard
ShardID vs ShardPredicate), the explicit-StartTsNs override path, and
the Cursor.MinTsNs fallback when StartTsNs=0. Side-effect-only
function; tests pin compile-time shape and visit each code path.

Scheduler pipelineFanout.InjectEvent (5):
- nil event silently absorbed (no follow-up panic in receiving
  pipeline)
- unknown shard returns nil (forward-compat for future shard-mapping
  gaps)
- known shard succeeds
- ctx cancellation propagates when underlying pipeline's buffer fills
- routes to the correct pipeline among multiple, with cross-pipeline
  isolation proven via per-pipeline buffer state

* test(s3/lifecycle): rename canceled to canceledCtx in fanout test

Per gemini review on #9412: a bare 'canceled' identifier reads like
a bool. Rename to canceledCtx so the type is obvious at the call site.

weed/s3api/s3lifecycle/reader/event_predicates_test.go

@@ -0,0 +1,47 @@
+package reader
+
+import (
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
+	"github.com/stretchr/testify/assert"
+)
+
+// IsCreate / IsDelete are the small but routing-critical predicates
+// the dispatcher uses to decide which match path applies. Both were
+// previously exercised only through end-to-end Tick/Match tests; pin
+// them directly here.
+
+func TestEventIsCreate_PopulatedNewEntryNoOldEntry(t *testing.T) {
+	e := &Event{NewEntry: &filer_pb.Entry{Name: "k"}}
+	assert.True(t, e.IsCreate())
+	assert.False(t, e.IsDelete())
+}
+
+func TestEventIsDelete_PopulatedOldEntryNoNewEntry(t *testing.T) {
+	e := &Event{OldEntry: &filer_pb.Entry{Name: "k"}}
+	assert.True(t, e.IsDelete())
+	assert.False(t, e.IsCreate())
+}
+
+func TestEventBothEntries_NeitherCreateNorDelete(t *testing.T) {
+	// An update event carries both old and new; the predicates are
+	// strict (one or the other, not both) so the router can route
+	// updates through the dedicated path rather than treating them
+	// as creates or deletes.
+	e := &Event{
+		OldEntry: &filer_pb.Entry{Name: "k"},
+		NewEntry: &filer_pb.Entry{Name: "k"},
+	}
+	assert.False(t, e.IsCreate(), "update event must not classify as create")
+	assert.False(t, e.IsDelete(), "update event must not classify as delete")
+}
+
+func TestEventNoEntries_NeitherCreateNorDelete(t *testing.T) {
+	// A degenerate event with neither side populated must not classify
+	// as either; otherwise a metadata-only filer event with no bucket
+	// payload could trigger spurious dispatches.
+	e := &Event{}
+	assert.False(t, e.IsCreate())
+	assert.False(t, e.IsDelete())
+}