Diagnosis is not accountability

When a seam fails, two questions arrive at once. What actually happened, and who is answerable. Asking them in the same conversation guarantees you get a poor answer to the first.

The reason is not that people are dishonest. It is that an accurate account of a failure almost always includes something the speaker did, and a person who believes the answer will be used to assign blame will produce an account that is true, complete in every particular, and shaped.

So separate them, explicitly and out loud. The diagnosis conversation establishes what happened and what in the design allowed it. Nobody is assigned anything. The accountability conversation, if it is needed at all, happens afterwards and with the diagnosis already fixed in writing.

Saying this at the start of the first meeting does most of the work. "We are not deciding whose fault this is today, we are deciding what the process permitted" changes what people are willing to say, immediately.

The failure mode to watch for is a leader who says this and then acts on it anyway. You get one violation before the instrument is dead, and it does not come back.