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 (experimental)
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. This role only exists in the unattended build's outer loop; attended, the builder raises a disagreement with you directly and the spec is amended by agreement.
And bracketing all of it: you, at the two gates — approve the spec (your go, recorded in git as the move to docs/specs/) 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 boundaries that define the line.