Fix: Enforce single default storage connection

Previously, `StorageService.saveConnection` allowed multiple connections to be marked as `defaultForUploads: true` because it did not unset the flag on existing connections. This caused `loadFromStorage` (which uses `find`) to potentially pick up an old, invalid connection instead of the newly configured one, leading to a loop where the user is asked to configure credentials again.

This change modifies `saveConnection` to iterate through existing connections and unset `defaultForUploads` if the new connection is being saved as the default. This ensures the "default" invariant is maintained.

Added a unit test case to verify this behavior.

js/services/storageService.js

@@ -418,6 +418,16 @@ export class StorageService {
       account.connections = {};
     }
 
+    // If this connection is being set as default, unset others
+    if (meta.defaultForUploads) {
+      for (const key in account.connections) {
+        const conn = account.connections[key];
+        if (conn.meta) {
+          conn.meta.defaultForUploads = false;
+        }
+      }
+    }
+
     account.connections[connectionId] = {
       id: connectionId,
       provider: payload.provider || meta.provider,

tests/storage-service.test.mjs

@@ -155,4 +155,21 @@ describe("StorageService", () => {
     assert.strictEqual(c1.meta.defaultForUploads, false);
     assert.strictEqual(c2.meta.defaultForUploads, true);
   });
+
+  test("saveConnection() with defaultForUploads=true clears other defaults", async () => {
+    await storageService.unlock(pubkey, { signer: mockSigner });
+
+    // Save first connection as default
+    await storageService.saveConnection(pubkey, "conn_1", { provider: PROVIDERS.R2 }, { defaultForUploads: true });
+
+    // Save second connection as default
+    await storageService.saveConnection(pubkey, "conn_2", { provider: PROVIDERS.S3 }, { defaultForUploads: true });
+
+    const conns = await storageService.listConnections(pubkey);
+    const c1 = conns.find(c => c.id === "conn_1");
+    const c2 = conns.find(c => c.id === "conn_2");
+
+    assert.strictEqual(c1.meta.defaultForUploads, false);
+    assert.strictEqual(c2.meta.defaultForUploads, true);
+  });
 });