[kazinator]

My remark "if a program produces output with a well-defined syntax" was intended specifically to consider such cases, and set them aside.

I didn't communicate that clearly: syntax can be "well-defined" yet truncatable. I meant some kind of syntax that is invalid if any suffix is missing, including the entire message, or else an object of an unexpected type is produced.

(In the case of JSON, valid JSON could be output which is truncatable, like 3.14 versus 3.14159. If the output is documented and expected to be a dictionary, we declare failure if a number emerges.)

[Too]

When dealing with errors of integrating 100 different programs in a script, I don’t want to set aside special cases.

It should always behave the same. The exit code of a program is the agreed upon standard for this.