Macro define_extension_runtime 

define_extension_runtime!() { /* proc-macro */ }

Generate a standard extension module, preparation engine, and prepared operation.

Exactly one execution route must be supplied.

• execute_reads runs the operation inside the runtime-formed context and has this signature: fn<B: Engine + ?Sized>(&OpType, &[TensorRead<'_>], &mut ExtensionExecutionContext<'_, B>). The generated owner entry opens the backend session and the context borrows it (B is dyn Engine), so the callback never runs on the owner. Prefer the session route below for new extensions.
• the session route (execute_in_session + session_supported) is the preferred one: session_supported has signature fn<B: BackendBound + 'static>(&OpType) -> bool and execute_in_session has signature fn(&OpType, &mut dyn Engine, &mut ExtensionCacheStore, &[TensorRead<'_>]). With it, the generated owner entry forms the session itself and hands the extension only a session, so no operation ever runs on the owner.

The removed legacy execute argument is rejected, not silently ignored.