most subagent tool have in the tool the sub agent calls to notify completion the message to return and a good documentation about how to return things, so the orchesrtator can orchestrate.

the harness that don't have that mechanism can have it augmented by prompt

roo code has a good harness for that (but terrible default prompts for the agents), kiro does that well too, gemini has a few misses as it just send off things without really caring of returns by default (albeit very model dependent), meanwhile jules using the same models has a good harness with a good feedback loop.