Unit 04.00: What actually needs to travel between steps

State is what survives from one step to the next. Deciding what goes in it is a design decision, not an accumulation.

Two questions per field

Could it be written down and read back? And would resuming be wrong without it?

The table below sorts seven candidates.

CANDIDATE                        CARRY?  WHY
the original request             yes     needed to resume
invoice id and contract id       yes     small, and they re-fetch the rest
full text of both documents      no      large; the ids retrieve it again
the decision so far              yes     resuming is wrong without it
every intermediate draft         no      only the current one matters
the API credential               no      a secret; not state
attempts, already-acted flags    yes     resuming is wrong without them

4 of 7 travel

The credential fails both tests in the way that matters: it could technically be serialised and must not be, because state gets written to a store and a store is a place secrets then live.

The document text is the interesting case. It serialises fine and resuming works without it, because the ids re-fetch it. Carrying it anyway is the most common way a state object becomes large enough to be a problem.

The mistake this prevents

The mistake is putting the whole response of every step into state because it might be useful. State is passed to every subsequent step and written at every checkpoint, so "might be useful" is paid for repeatedly.

Takeaway

Carry what resuming requires and nothing else: ids over contents, never credentials, nothing that cannot be written down.

Mark complete