Fix clipboard read-policy bypass and lock-held file checks

- copied_file: check the read policy on the real path when it is
  valid UTF-8; skip non-UTF-8 paths while automation roots are
  active instead of checking a lossy name (path traversal via
  symlink, CodeRabbit #3872 thread 1).
- full_bytes_cached: collect matching cache candidates under the
  FULL lock, then run the read checks after releasing it, so
  filesystem walks no longer stall other FULL users (thread 2).

apps/vectorcraft/src/clipboard.rs

@@ -144,7 +144,12 @@ fn copied_file(paths: Vec<PathBuf>, mimes: &[&'static str]) -> Option<Flavour> {
             _ => path,
         };
         // A paste sent by automation reads only what its roots allow.
-        vectorcraft_engine::file_access::check_read(&path.to_string_lossy()).ok()?;
+        match path.to_str() {
+            Some(p) => vectorcraft_engine::file_access::check_read(p).ok()?,
+            // A lossy name would check another file than the one opened.
+            None if vectorcraft_engine::file_access::current().is_none() => {}
+            None => return None,
+        }
         let mut head = Vec::with_capacity(FILE_HEAD);
         std::fs::File::open(&path).ok()?.take(FILE_HEAD as u64).read_to_end(&mut head).ok()?;
         let mime = file_flavour(&path.to_string_lossy(), &head, mimes)?;

crates/doc/src/placed_document.rs

@@ -320,7 +320,10 @@ pub fn full_bytes_cached(p: &PlacedDocument, blob: &ImageBlob) -> Option<Arc<Vec
         return Some(blob.bytes.clone());
     }
     let allowed = |path: &str| READ_CHECK.get().is_none_or(|ok| ok(path));
-    full().iter().rev().find(|(k, path, _)| *k == p.key && allowed(path)).map(|(_, _, b)| b.clone())
+    // Copy the candidates, newest first, so the filesystem checks run without the lock.
+    let candidates: Vec<(String, Arc<Vec<u8>>)> =
+        full().iter().rev().filter(|(k, _, _)| *k == p.key).map(|(_, path, b)| (path.clone(), b.clone())).collect();
+    candidates.into_iter().find(|(path, _)| allowed(path)).map(|(_, b)| b)
 }
 
 /// The file's bytes: stored, read again already, or read again now ([`set_file_reader`]). `None`