Add Files to the universal canvas rail and sidebar flow, with a reusable floating surface modal chrome that matches Browser/Desktop behavior.
Make the File Browser modal draggable/resizable with Focus mode, keep Editor on the same draggable modal helper, and preserve dock/undock handoff state.
Harden File Browser startup so empty paths resolve to the default workdir, restyle the Up control, compact New file/New folder actions, and hide Modified before Name/Size in narrow containers.
Update DOX contracts and focused regression coverage for the new Files surface, modal chrome, default-path fallback, and compact layout behavior.
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