There is a neat trick buried in this thread explaining how to turn off the status LED except for exceptions: Disabling Status LED - General - Particle
There remains undocumented (and perhaps unimplemented) the effect of the TTL param in Spark.publish()
Meaning of ttl parameter in Spark.publish() - Firmware - Particle - There are other questions too: Publish & subscribe semantics & documentation - Firmware - Particle
It has recently become clear TTL is unimplemented.
There is uncertainty as to how much of the gcc build environment one can rely on when compiling in the cloud or even locally. E.G. Is UINT_MAX reliably the max unsigned int on the Spark Core? Which of the Posix/ANSI/Standard C functions can be used? (Unix manual ch 2) Which libc functions? (Unix manual ch 3). Which #defines can be relied on? Which #defines are additionally defined?
Related is the definition of the language itself, and portability issues, and the fact that not even all the functions available are listed in the Spark docs: