[ovasylenko]

A native callback waiting for a physical thread could enter host code after its remote lease expired if the runtime and timer driver were stalled. Ready work could also advance before the delayed lease timer ran.

Publish read-only monotonic lease authority, revoke it before supervised futures are destroyed, and check it at physical mobile callback entry and result publication. Keep the existing local handler registration API and StepContext shape compatible.

Validation:

• Reproduced the real queued-callback failure on clean main at 8e23c25; the same regression passes with this fix.
• All 711 mobile tests passed on the isolated main-based checkout.
• All 16 lease, three registry and 27 executor tests passed.
• Strict all-target workspace Clippy, the actual WASM target and formatting passed.

Full CI and Mobile SDK workflow success are required before merge.