Function lumen_signal_get_str 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn lumen_signal_get_str(
    name: *const c_char,
    buf: *mut c_char,
    buf_len: usize,
    out_len: *mut usize,
) -> LumenStatus

Read a scalar signal as a UTF-8 string into a caller-provided buffer.

On success copies the value plus a trailing NUL into buf and, when out_len is non-null, sets *out_len to the byte length (excluding the NUL). When buf is null or buf_len is too small, sets *out_len to the required capacity (byte length + 1) and returns LumenStatus::ErrBufferTooSmall without writing buf; call once with a null/zero buffer to size it, then again to fill.

Returns LumenStatus::ErrBadArg when name is null / non-UTF-8, or when the signal holds no string.

Scope: this reads back the string the embedder last pushed through the FFI (a clear leaves an empty string). A string written inside the running app lands in PropertyStore, which the cross-thread mirror keeps for numbers, bools, and colors only, so it is not visible here.