Module note 

What a protocol says about a decision it took.

The simulator’s trace records what happened to a protocol — what it sent, what was delivered, what it wrote. It cannot record what the protocol decided, and it is completely silent about a decision whose outcome was to do nothing. That is the case that has cost this project the most: a leader trusted by everyone that announced nothing left no trace event at all, and finding it meant bisecting the whole stack by hand.

A note earns its place only where the trace cannot say it

The rule, and it is the one that keeps narration from decaying. A note beside cx.indicate(Ind::StartEpoch { ts, leader }) restating the same thing adds nothing a reader could not already see, and the two can now disagree — which is exactly how the docstring that quoted a deadlocking resend clause its own comment said a test had replaced went wrong.

Three things qualify:

• a decision that produced no effect at all — a message refused, a candidate already passed;
• why an effect was produced, where the effect alone is ambiguous — epoch_change sends the same NACK on the wire whether it is refusing an announcement or volunteering how far it has reached, and a reader of the trace cannot tell those apart;
• nothing else, yet. The vocabulary grows one narrated module at a time.

One vocabulary per run

A note’s type belongs to the run rather than to a layer, exactly as a TimerId does: a composed stack narrates in one vocabulary, and a note passes through composition untouched, with no mapper and nothing for a parent to re-wrap. A parent letting a child’s note through is not endorsing it — the decision was the child’s.

That is why every protocol in this crate declares type Note = Note, including the twenty-five that narrate nothing. The alternative — each layer naming its own vocabulary and parents converting — was built and discarded: it put a where clause relating two type parameters on every layer generic over a port, to express something no layer actually wanted to do.

Enums

Note

A decision a protocol took, in the vocabulary this stack narrates in.

Refusal

Why something was refused or ignored.