feat(downloads): WiFi-only network-type-aware download gating

Add a metered/cellular network detector so downloads honour a "WiFi
only" preference. Android reports network type via NetworkTypeMonitor;
Rust exposes it through download/network.rs and holds the queue pump when
on a metered connection, emitting a queue-wide waitingForNetwork event.
The frontend surfaces this via the networkType service and a
waitingForNetwork store flag.

TRACES: UR-053 | DR-074

src/lib/stores/downloads.test.ts

@@ -309,6 +309,35 @@ describe("downloads store", () => {
       expect(state.stats.queuedCount).toBe(1); // 1 pending
     });
 
+    // The Transfers view shows only in-flight rows; a completed transfer must
+    // NOT appear there (it lives in Downloaded). Mirrors the /downloads page's
+    // `transfers` derivation: active + pending + failed.
+    // TRACES: UR-055 | DR-084 | UT-052
+    it("transfers set excludes completed downloads", async () => {
+      const { downloads, activeDownloads, pendingDownloads, failedDownloads } = await import(
+        "./downloads"
+      );
+
+      mockInvoke.mockResolvedValueOnce({
+        downloads: [
+          { id: 1, itemId: "a", userId: "u", filePath: "/a", status: "downloading", progress: 0.5, bytesDownloaded: 5, queuedAt: "t", retryCount: 0, priority: 0, mediaType: "audio", downloadSource: "user" },
+          { id: 2, itemId: "b", userId: "u", filePath: "/b", status: "pending", progress: 0, bytesDownloaded: 0, queuedAt: "t", retryCount: 0, priority: 0, mediaType: "audio", downloadSource: "user" },
+          { id: 3, itemId: "c", userId: "u", filePath: "/c", status: "completed", progress: 1, bytesDownloaded: 9, queuedAt: "t", retryCount: 0, priority: 0, mediaType: "audio", downloadSource: "user" },
+          { id: 4, itemId: "d", userId: "u", filePath: "/d", status: "failed", progress: 0, bytesDownloaded: 0, queuedAt: "t", retryCount: 1, priority: 0, mediaType: "audio", downloadSource: "user" },
+        ],
+        stats: { total: 4, activeCount: 1, queuedCount: 1, completedCount: 1, failedCount: 1, pausedCount: 0 },
+      });
+
+      await downloads.refresh("u");
+
+      const transfers = get(activeDownloads)
+        .concat(get(pendingDownloads))
+        .concat(get(failedDownloads));
+      const ids = transfers.map((d) => d.id).sort();
+      expect(ids).toEqual([1, 2, 4]);
+      expect(transfers.some((d) => d.status === "completed")).toBe(false);
+    });
+
     it("should support status filter", async () => {
       const { downloads } = await import("./downloads");
 

src/lib/stores/downloads.ts

@@ -40,7 +40,16 @@ export interface DownloadInfo {
 }
 
 export interface DownloadEvent {
-	type: 'queued' | 'started' | 'progress' | 'completed' | 'failed' | 'paused' | 'cancelled';
+	type:
+		| 'queued'
+		| 'started'
+		| 'progress'
+		| 'completed'
+		| 'failed'
+		| 'paused'
+		| 'cancelled'
+		| 'waitingForNetwork';
+	/** Absent on 'waitingForNetwork', which is queue-wide rather than per-download. */
 	downloadId: number;
 	itemId: string;
 	bytesDownloaded?: number;
@@ -64,6 +73,15 @@ interface DownloadsState {
 	stats: DownloadStats;
 }
 
+/**
+ * True when the download queue is held because "WiFi Only" is enabled and the
+ * device is on a metered/cellular network. Pending rows stay pending; the queue
+ * resumes automatically when an acceptable network appears.
+ *
+ * TRACES: UR-053 | DR-074
+ */
+export const waitingForNetwork = writable(false);
+
 function createDownloadsStore() {
 	const { subscribe, update, set } = writable<DownloadsState>({
 		downloads: {},
@@ -607,6 +625,17 @@ function handleDownloadEvent(payload: DownloadEvent): void {
 		case 'cancelled':
 			removeDownloadFromStore(payload.downloadId);
 			break;
+
+		case 'waitingForNetwork':
+			// Queue-wide, not tied to one download: the pump refused to start
+			// anything because WiFi-only is on and we're on a metered network.
+			waitingForNetwork.set(true);
+			break;
+	}
+
+	// Any per-download progress proves the gate isn't holding us any more.
+	if (payload.type === 'started' || payload.type === 'progress') {
+		waitingForNetwork.set(false);
 	}
 }