Constant FN_BOOL_FLAGS_HELP 

const FN_BOOL_FLAGS_HELP: &str = "invisible, visible, check_interrupt, worker, no_worker, coerce, no_coerce, \
     rng, unwrap_in_r, serialize, serde_error, strict, no_strict, \
     preconditions, no_preconditions, internal, noexport, export, call_arg";

Comma-separated list of all fn-level boolean flags, for error messages.

Kept as a single constant so the three “unknown option” error paths (Path, NameValue bool, parenthesized bool) all read from the same list and can’t drift.