fix(core,fuse): back failed uploads off properly and spread their retries

A reconnect made every failed op due at once, quota and access refusals
included, and ops that failed together retried in the same second. The
doubling also stopped at 128 s, short of the 300 s maximum. Reconnects
now move up only unrefused ops, and the backoff reaches its maximum with
a per-op spread of up to a fifth (B237).

crates/pdfs-core/src/db/tests.rs

@@ -7531,6 +7531,32 @@ fn a_refused_change_names_its_node_by_local_id() {
     );
 }
 
+/// A reconnect moves up the ops that failed for want of a link. One Drive
+/// refused, for quota or access, keeps its backoff: the link coming back
+/// changes nothing about it. "Retry all" still moves both.
+#[test]
+fn a_reconnect_leaves_refused_ops_to_their_backoff() {
+    let db = Db::open_in_memory().unwrap();
+    let offline = queued_op(&db, "vol~a", 2, 90_000);
+    let refused = queued_op(&db, "vol~b", 2, 90_000);
+    db.set_op_issue(refused, Some("quota")).unwrap();
+
+    assert_eq!(db.retry_unrefused_ops_now(5_000).unwrap(), 1);
+    let due = |id: i64| {
+        db.pending_ops()
+            .unwrap()
+            .into_iter()
+            .find(|op| op.id == id)
+            .unwrap()
+            .next_attempt_at
+    };
+    assert_eq!(due(offline), 5_000);
+    assert_eq!(due(refused), 90_000);
+
+    assert_eq!(db.retry_failed_ops_now(5_000).unwrap(), 1);
+    assert_eq!(due(refused), 5_000);
+}
+
 #[test]
 fn retry_all_touches_only_ops_that_have_failed() {
     let db = Db::open_in_memory().unwrap();