When Does a One-Time Yes Become an Ongoing Commitment?

You agree to help with one small thing. A few weeks later, it has quietly become part of the routine—and neither person remembers agreeing to that version of the arrangement.

How do you make the boundary between a one-time yes and ongoing availability clear without making collaboration feel cold? Is it easier to name the limit when you first agree, or to check in once the pattern starts to change?