Function export_once 

pub fn export_once() -> bool

Idempotent export: writes HTML and/or JSON to the configured output path. Called by the on-demand path (trigger_export_now, periodic flusher).

Equivalent to export_for_reason(ExportReason::OnDemand). The exit paths (Drop, panic, signal) call export_for_reason directly so their per-path enable flags (on_exit, on_panic) are consulted.

Returns true if THIS call performed the export; false if a prior call already exported, or if no tracker/cfg is installed.

Re-entrancy safety

[EXPORTED] is set to true via swap BEFORE the export work begins. If the export itself panics, the re-entrant panic-hook invocation sees [EXPORTED] already true and returns false — no infinite recursion.