ffi-capsule-protocol

First enumerate existing getters with grep over crates/ and examples to match the established signature shape. The getter takes the session it is installed on, returns a PyCapsule, and needs a corresponding extraction helper added in crates/util/src/lib.rs.

FFI_TaskContextProvider holds its provider weakly, so a SessionContext constructed inline in the getter is dropped before the capsule is used. Take the provider from the passed-in session via ffi_task_context_provider_from_pycapsule instead of building a new context.

No. A fresh SessionContext is the wrong registry, so UDFs the host registered are invisible during decode, and its weak handle dangles. Use the *_with_ffi_codec constructors with codecs extracted from the host session.

Yes. Extension libraries implement these methods, so a signature change breaks them with a bare TypeError. Add an upgrade-guide entry, apply the api change label, reuse call_capsule_getter for diagnostics, and update the Protocol hints in context.py and user_defined.py.

FFI codecs carry weak handles bound to one Arc<SessionContext> allocation. Replacing the allocation orphans every registered FFI provider and codec, so mutate state via state_ref().write() and preserve the session id across the rewrite.