Optional hook invoked right before FCQRS kills the process on a fatal
 error. FailFast skips finalizers and ProcessExit handlers, so without
 this everything still sitting in a batch exporter or buffered log sink
 is silently dropped — including the span and log entry of the fatal
 flow itself (every fatal site logs before invoking this hook). Flush
 your whole pipeline here, e.g.
   Telemetry.FatalFlush <- Action(fun () ->
       tracerProvider.ForceFlush(3000) |> ignore
       loggerProvider.ForceFlush(3000) |> ignore) // or Serilog's Log.CloseAndFlush()
 It runs on a background thread with a 5-second cap so a hung exporter
 cannot block the kill.

Process-wide switch for including rendered message *payloads* in diagnostics. Default: on. Span *names* are always low-cardinality case names (e.g. "Command:Register") regardless of this switch — payload values never appear there, so per-operation tracing rules and trace-viewer grouping always work, and nothing sensitive leaks into the indexed span name. This switch governs the *detail*: the payload rendered into span tags (command.type / event.type) and into the message-flow log lines. Turn it off (Telemetry.IncludePayloads <- false, or FcqrsBuilder.WithPayloadDiagnostics(false)) for sensitive domains — tags and log lines then carry the case name only, matching the span name.

Process-wide switch for the message-flow narrative logs. Default: on.