fix(fuse): keep inode stable across rename

relocate() called forget(), dropping the node's by_uid mapping, so
the re-enumeration assigned a fresh inode. The kernel had already
carried the renamed dentry onto the old one and holds it for the
entry TTL, so lookup/getattr/opendir resolved to an inode entries
no longer held and returned ENOENT — while readdir walked children
and reported the new inode. A renamed directory listed in its
parent but could not be entered until the TTL expired.

Rewrite the node in place and invalidate both parents' listings
instead. Also stops the moved node's DB row being deleted and
recreated on every move, which the B1 data-loss fix worked around

crates/pdfs-core/src/config.rs

@@ -1,6 +1,6 @@
 //! Static client identity and per-user filesystem paths.
 
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 use directories::ProjectDirs;
 use serde::{Deserialize, Serialize};
@@ -165,18 +165,104 @@ impl AppDirs {
             .unwrap_or_else(|| self.default_mountpoint())
     }
 
-    /// Create state + cache dirs if missing.
+    /// Create state + cache dirs if missing, owner-only.
+    ///
+    /// The mode is set explicitly rather than left to the umask. These
+    /// directories hold decrypted file content, a plaintext index of every node
+    /// name in the Drive, and the control socket — and `create_dir_all` under a
+    /// typical umask makes them `0755`. Until this was fixed, the only thing
+    /// keeping another local user out was `~/.cache` and `~/.local/state`
+    /// happening to be `0700`, which is a convention of the user's system and
+    /// not something this client established (bugs.md B6).
+    ///
+    /// Applied on every start, not just at creation: a directory that already
+    /// exists with a permissive mode — restored from a backup that flattened
+    /// modes, or created by an older build — is tightened here.
     pub fn ensure(&self) -> Result<()> {
-        std::fs::create_dir_all(self.state_dir())?;
-        std::fs::create_dir_all(self.cache_dir())?;
-        let _ = std::fs::create_dir_all(self.dirs.config_dir());
+        for dir in [self.state_dir(), self.cache_dir()] {
+            std::fs::create_dir_all(&dir)?;
+            restrict_dir(&dir);
+        }
+        let config_dir = self.dirs.config_dir().to_path_buf();
+        if std::fs::create_dir_all(&config_dir).is_ok() {
+            restrict_dir(&config_dir);
+        }
         Ok(())
     }
 }
 
+/// Make `dir` owner-only (`0700`). Best effort: a mode we cannot set (an
+/// exotic filesystem, a directory we do not own) is not worth refusing to
+/// start over, and the caller has no better answer than continuing.
+fn restrict_dir(dir: &Path) {
+    use std::os::unix::fs::PermissionsExt;
+    if let Err(e) = std::fs::set_permissions(dir, std::fs::Permissions::from_mode(0o700)) {
+        tracing::warn!(path = %dir.display(), error = %e, "could not restrict directory to 0700");
+    }
+}
+
+/// Make a just-bound Unix socket owner-only (`0600`).
+///
+/// Connecting to the control socket drives the daemon with its authenticated
+/// session — enumerate, read, upload, trash, share — without presenting any
+/// credential, since the daemon already holds one. It is an authority boundary,
+/// not merely private data, and `UnixListener::bind` applies the umask like any
+/// other file (bugs.md B6).
+///
+/// There is a window between `bind` and this call during which the socket
+/// carries the umask's mode. It is closed in practice by the containing
+/// directory: [`Dirs::ensure`] has already made the state directory `0700`, so
+/// nothing else can reach the socket to exploit the window.
+pub fn restrict_socket(path: &Path) -> Result<()> {
+    use std::os::unix::fs::PermissionsExt;
+    std::fs::set_permissions(path, std::fs::Permissions::from_mode(0o600))?;
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::os::unix::fs::PermissionsExt;
+
+    fn mode_of(p: &Path) -> u32 {
+        std::fs::metadata(p).unwrap().permissions().mode() & 0o777
+    }
+
+    /// bugs.md B6. A permissive mode here is not a cosmetic problem: these
+    /// directories hold decrypted content, a plaintext index of every node name,
+    /// and the control socket that commands the daemon's session.
+    #[test]
+    fn restrict_dir_makes_a_directory_owner_only() {
+        let dir = std::env::temp_dir().join(format!("pdfs-cfg-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(&dir).unwrap();
+        // Start deliberately world-readable, as `create_dir_all` under a typical
+        // umask would leave it.
+        std::fs::set_permissions(&dir, std::fs::Permissions::from_mode(0o755)).unwrap();
+
+        restrict_dir(&dir);
+
+        assert_eq!(mode_of(&dir), 0o700, "group and other must have no access");
+        let _ = std::fs::remove_dir_all(&dir);
+    }
+
+    /// Connecting to the control socket confers the daemon's authenticated
+    /// session with no credential, so it is an authority boundary rather than
+    /// merely private data.
+    #[test]
+    fn restrict_socket_makes_a_socket_owner_only() {
+        let dir = std::env::temp_dir().join(format!("pdfs-sock-{}", std::process::id()));
+        let _ = std::fs::remove_dir_all(&dir);
+        std::fs::create_dir_all(&dir).unwrap();
+        let sock = dir.join("control.sock");
+        let listener = std::os::unix::net::UnixListener::bind(&sock).unwrap();
+
+        restrict_socket(&sock).unwrap();
+
+        assert_eq!(mode_of(&sock), 0o600, "no other local user may connect");
+        drop(listener);
+        let _ = std::fs::remove_dir_all(&dir);
+    }
 
     #[test]
     fn test_app_config_serialization() {