Use vsock.sock_3 filename for Firecracker

Author: richiemcilroy

crates/sandchest-node/src/jailer.rs

@@ -107,8 +107,11 @@ impl JailerConfig {
     }
 
     /// Host-visible vsock socket path for a jailed VM.
+    ///
+    /// Firecracker creates the host-side UDS at `{uds_path}_{guest_cid}`.
+    /// Guest CID is always 3, so the actual file is `vsock.sock_3`.
     pub fn host_vsock_path(&self, sandbox_id: &str) -> PathBuf {
-        self.chroot_root(sandbox_id).join("vsock.sock")
+        self.chroot_root(sandbox_id).join("vsock.sock_3")
     }
 
     /// Convert a host-absolute path to a chroot-relative path.
@@ -401,7 +404,7 @@ mod tests {
         let path = config.host_vsock_path("sb_test123");
         assert_eq!(
             path,
-            PathBuf::from("/var/sandchest/jailer/firecracker/sb_test123/root/vsock.sock")
+            PathBuf::from("/var/sandchest/jailer/firecracker/sb_test123/root/vsock.sock_3")
         );
     }
 

crates/sandchest-node/src/sandbox.rs

@@ -124,7 +124,7 @@ impl SandboxManager {
             let dir = format!("{}/sandboxes/{}", self.node_config.data_dir, sandbox_id);
             SandboxPaths {
                 api_socket: format!("{}/api.sock", dir),
-                vsock: format!("{}/vsock.sock", dir),
+                vsock: format!("{}/vsock.sock_3", dir),
                 chroot_root: None,
                 data_dir: dir.clone(),
                 dir,