fix(fuse): a file landing while its folder is pinned stays available offline (B208)

A folder pin reads each file's modification time and size before it
downloads the file. If the file's create landed during the download, the
landing set Drive's time, and the pin then stored the blob under the old
time. The file showed as kept offline but read as stale.

After each download, the pin now compares the file's time and size with
the tree's. If they changed, it downloads the file again under the new
values, at most three times.

The simulation gains FakeClient::hold_next_download to force that order.

crates/pdfs-fuse/src/lib.rs

@@ -4290,7 +4290,7 @@ impl Core {
                         return;
                     }
                     job.detail(file.clone());
-                    if let Err(e) = self.fetch_content(&uid, &file, mtime, size) {
+                    if let Err(e) = self.fetch_pinned(&uid, &file, mtime, size) {
                         warn!(%uid, error = %e, "pin folder: download failed");
                         failed += 1;
                     }
@@ -4302,6 +4302,30 @@ impl Core {
         }
     }
 
+    /// Cache the file `uid` for a folder pin. Its `mtime` and `size` were read
+    /// before the download, and a create landing or a remote edit can change
+    /// them while it runs. The blob is then stored under the old ones and reads
+    /// as stale, so the file is listed as kept but not available offline. Fetch
+    /// it again under the new ones, a few times at most.
+    fn fetch_pinned(&self, uid: &NodeUid, name: &str, mtime: i64, size: u64) -> CoreResult<()> {
+        let mut fetched = (mtime, size);
+        for _ in 0..3 {
+            self.fetch_content(uid, name, fetched.0, fetched.1)?;
+            let current = {
+                let st = self.state();
+                st.by_uid
+                    .get(uid)
+                    .and_then(|ino| st.entries.get(ino))
+                    .map(|e| (e.node.modification_time, node_size(&e.node)))
+            };
+            match current {
+                Some(now) if now != fetched => fetched = now,
+                _ => break,
+            }
+        }
+        Ok(())
+    }
+
     /// Every file in the subtree rooted at folder `ino`.
     fn pin_subtree_files(&self, ino: u64) -> CoreResult<Vec<(NodeUid, String, i64, u64)>> {
         let mut files: Vec<(NodeUid, String, i64, u64)> = Vec::new();