[LinuxBoy-96]

• Problem: the set_parent_of handler calls with_states(&child, …), which locks the child surface's state, and inside that closure calls is_valid_parent(child, parent). That function first calls is_toplevel_equivalent(parent) → get_role(parent), which locks the parent surface's state. When parent and child are the same surface (export a toplevel, import the handle, then set_parent_of the same surface), it re-locks the same non-reentrant mutex and deadlocks. The parent-loop guard (*child == parent) is meant to reject exactly this, but it runs only after the re-lock.
• When: any client binds zxdg_exporter_v2 + zxdg_importer_v2, exports one of its toplevels, imports the handle, and calls set_parent_of with that same surface. The global is unfiltered.
• Consequence: the compositor's main thread deadlocks (confirmed: 0% CPU, waiting on a futex); it stops serving every client — a full session freeze, never caught.
• Fix (smithay): resolve the parent's role and run is_valid_parent before taking with_states(&child), or special-case parent == child.

Checklist

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