Implement resumable download queue (T-301)

core/application/download_event.go

@@ -0,0 +1,45 @@
+package application
+
+// DownloadStartedPayload begins one transfer attempt. A later attempt may
+// reset Done when a remote entity cannot be safely resumed.
+type DownloadStartedPayload struct {
+	Attempt    uint64
+	Done       int64
+	TotalKnown bool
+	Total      int64
+}
+
+// DownloadProgressPayload reports monotonic progress within one attempt.
+type DownloadProgressPayload struct {
+	Attempt       uint64
+	Done          int64
+	TotalKnown    bool
+	Total         int64
+	SpeedBytesSec int64
+}
+
+// DownloadPausedPayload maps to domain queued while preserving pause intent.
+type DownloadPausedPayload struct {
+	Attempt uint64
+	Done    int64
+}
+
+// DownloadCompletedPayload means bytes are durably downloaded but still
+// untrusted. T-302 must verify the signed Catalog identity, size and hashes.
+type DownloadCompletedPayload struct {
+	Attempt uint64
+	Done    int64
+	Path    string
+}
+
+// DownloadFailedPayload carries a stable low-level transfer/storage code.
+type DownloadFailedPayload struct {
+	Attempt   uint64
+	Done      int64
+	ErrorCode string
+}
+
+// DownloadCanceledPayload confirms cleanup and suppresses the old attempt.
+type DownloadCanceledPayload struct {
+	Attempt uint64
+}