Four actors, one line
Specline isn't one experience — it's four, connected, with a hard line running through them. The line is simple: a machine checks that the spec is complete; people and agents judge whether the work is right. Specline never judges meaning, because the moment a tool grades good instead of present, it's wrong in ways you can't predict. So judgment stays with the four who can carry it.
The product owner — writes the spec
Defines what the feature is for, what "done" means in checkable terms, and what's deliberately out. Brings product judgment; doesn't write code. This is who the assistant helps and who holds the two gates.
Specline — checks the spec is buildable
In the planning phase, confirms the spec folder has everything an agent needs. Deterministic, structural, no judgment. Guarantees the spec is answerable — not that it's good.
The implementer agent — builds it
Equipped with the codebase's standards (conventions/, technical/) and what already exists (the relations graph), it builds from the spec until it can establish the goal is met — then stops and hands to review.
The reviewer agent — checks the interpretation
A fresh, outside agent that judges how the implementer interpreted the spec against the goal and the standards — including the nuanced bars, like performance and security, the goal can't fully state.
And bracketing all of it: you, at the two gates — ratify the spec by merging it to main before the build, accept the result after. The whole point of the consistent shape is that it equips the agents in the middle; the whole point of the gates is that the irreducible judgment stays human. The rest of the handbook walks these four through one feature — but first, the thing they all read: the spec itself.
Reference: the seven boundaries that define the line.