Macro debug_trace 

macro_rules! debug_trace {
    ($($arg:tt)*) => { ... };
}

Conditionally print debug trace output to stderr.

When FTUI_DEBUG_TRACE=1 is set, prints timestamped debug messages. When disabled, compiles to a single bool check (effectively zero cost).

Example

debug_trace!("subscription started: id={}", sub_id);
debug_trace!("main loop heartbeat: frame={}", frame_count);