Knowledge that lives in people's heads leaves when they do
A small senior team runs on shared understanding, and shared understanding rots fast if it is never written down. The discipline that keeps a team fast as it grows is turning decisions into documents and documents into tickets, in one place, so that the reasoning behind the work is recoverable months later by someone who was not in the room.
Spec first, then ticket
The cheapest bug is the one argued out of existence before any code is written. Write a short spec for anything non trivial: what we are building, why, what is explicitly out of scope, and how we will know it works. Only once that is settled do you break it into tickets. The spec is the source; the tickets are derived from it, not the other way around.
A good spec is short and decisive. It names the constraints, records the alternatives considered, and commits to one approach. That record is what stops the team relitigating the same decision every time someone new asks why it was done this way.
One hub, linked to the work
Keep the docs and the project tracking in the same workspace, and link the ticket back to the spec and the spec forward to the tickets. When a question comes up during the build, the answer is one click away in the document that decided it, instead of lost in a scroll of chat messages.
Capture decisions as they happen
The knowledge worth keeping is not just the spec, it is the small decisions made along the way: why a library was chosen, why a shortcut was taken, what the known gap is. Writing those down as they happen, in the doc next to the work, is what turns a project's history into something a new team member can read rather than reconstruct.
Why it compounds
Documentation feels like overhead in the moment and pays back every time someone avoids redoing settled work, onboards without a week of hand holding, or answers a buyer's question by pulling up the decision record. The observability layer surfaces what is breaking now; the documentation layer makes sure what the team learned does not have to be learned twice.