Find the edge cases

The code below is supposed to {{description}}.

List the inputs and states where it does something other than that. Work through:
empty, one element, exactly at the boundary, one past it, duplicates, nil, wrong
order of operations, and concurrent access.

For each, say what actually happens and how a user would notice. Rank them by how
likely a real user is to hit it, not by how clever the case is.

{{code}}

What to fill in

{{description}}

What the code is supposed to do — e.g. cap free-tier history at 25 items

{{code}}

The code — e.g. Paste it

What it produces

1. Exactly 25 items, free tier — off-by-one: is the 25th kept
   or evicted? User sees 24 and assumes a bug.
2. Downgrade with 500 items — the cap is applied against the
   previous fetch, so nothing changes until relaunch.
3. All 25 pinned — pinned items bypass the cap, so the
   "last 25" promise silently becomes 50.