Function guarded_ffi_call 

pub fn guarded_ffi_call<F, R>(f: F, mode: GuardMode, source: PanicSource) -> R
where
    F: FnOnce() -> R,

Execute f inside an FFI guard selected by mode.

On panic:

• Extracts the panic message from the payload.
• Fires crate::panic_telemetry with source.
• For GuardMode::CatchUnwind: raises R error via Rf_error (diverges — never returns).
• For GuardMode::RUnwind: delegates to with_r_unwind_protect_sourced.

Parameters

• f: The closure to execute.
• mode: Which guard strategy to use.
• source: Attribution for telemetry if a panic occurs.

Note on fallback

GuardMode::CatchUnwind diverges on panic (Rf_error never returns), so no fallback value is needed. If you need a fallback (e.g. connection trampolines that must return a value on panic without calling R), use guarded_ffi_call_with_fallback instead.