Artifact: Which Change Earns an ADR

ex-32 · exercises co-18 · three changes, only one hard-to-reverse enough to record.

Change	Hard to reverse?	Architecturally significant?	Earns an ADR?
Rename a local variable d to delta inside restock()	No -- a single-file, single-commit revert	No -- purely cosmetic, zero external impact	No
Add one logger.info(...) line inside the redemption handler	No -- trivially removable	No -- observability detail, not a structural choice	No
Swap the primary datastore from PostgreSQL to a document store for the card-balance table	Yes -- touches every read/write path, a data-migration project to undo	Yes -- changes the system's own storage/consistency model	Yes

Verify: only the database swap earns an ADR -- both other changes fail BOTH tests (hard to reverse, architecturally significant), while the database swap passes both, satisfying co-18's rule that a routine change does not earn one.

Key takeaway: an ADR-worthy decision fails to reverse cheaply AND changes the system's own structure -- either property alone is not enough (a hard-to-reverse but purely cosmetic rename does not exist in practice; an easily-reversible architectural experiment behind a flag might not need one yet either).

Why It Matters: writing an ADR for every commit drowns the genuinely significant decisions in noise, defeating the entire point of having a searchable decision record; the two-question test (reversibility, architectural significance) keeps the ADR log small enough that someone six months later will actually read the one that matters.