test(uploads): jobSink forwards the tracker's timestamp to the store (#51)

The worker fake ignored the heartbeat time, so the store-boundary half of the app-clock
fix had no assertion. Found by the PR #58 review.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/uploads/jobsink_test.go

@@ -0,0 +1,48 @@
+package uploads
+
+// Observes what jobSink hands the store: the heartbeat's timestamp is the one the tracker
+// stamped (its application clock), not a second reading taken here (#51).
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"git.d-ma.be/mathias/tapir/internal/domain"
+)
+
+type atStore struct{ beatAt, saveAt time.Time }
+
+func (*atStore) StartTranscribing(context.Context, string, string) error { return nil }
+func (*atStore) CompleteUpload(context.Context, string, string, domain.Transcription) error {
+	return nil
+}
+func (*atStore) FailUpload(context.Context, string, string, domain.UploadErrorKind) error { return nil }
+func (s *atStore) SaveProgress(_ context.Context, _, _ string, _ []domain.ProgressStep, at time.Time) error {
+	s.saveAt = at
+	return nil
+}
+func (s *atStore) Heartbeat(_ context.Context, _, _ string, at time.Time) error {
+	s.beatAt = at
+	return nil
+}
+
+func TestJobSink_ForwardsTheTrackersTimestampToTheStoreUnchanged(t *testing.T) {
+	st := &atStore{}
+	sink := jobSink{st: st, userID: "u", id: "i"}
+	stamp := time.Date(2020, 1, 2, 3, 4, 5, 0, time.UTC)
+
+	if err := sink.Beat(context.Background(), stamp); err != nil {
+		t.Fatal(err)
+	}
+	if err := sink.SaveProgress(context.Background(), nil, stamp); err != nil {
+		t.Fatal(err)
+	}
+
+	if !st.beatAt.Equal(stamp) {
+		t.Errorf("heartbeat reached the store stamped %v, want the tracker's %v", st.beatAt, stamp)
+	}
+	if !st.saveAt.Equal(stamp) {
+		t.Errorf("progress save reached the store stamped %v, want the tracker's %v", st.saveAt, stamp)
+	}
+}