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.

Deferred conditions signal on R’s main thread before return (or panic conversion). Use this boundary on the main thread. Any SEXP held in the generic result must be rooted, e.g. by returning OwnedProtect.

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.