It seems that the definition of "direct participation" was already very much subject to precedent and complicated. https://www.icrc.org/en/doc/resources/documents/faq/direct-participation-ihl-faq-020609.htm provides some interesting nonobvious examples
Interestingly, if one reads the interpretation provided in https://www.icrc.org/en/doc/assets/files/other/icrc-002-0990.pdf (specifically pp. 52-54), it seems to imply that setting up automatic observation posts that will report enemy movement should be considered to be _in_direct participation.