Nocturne

Nocturne is a Claude Code skill. A design-layer Claude reads the target repo, derives a quality gate from it, writes a harness tailored to that repo, and launches a headless loop against a checkbox backlog. The loop takes one task at a time, in an isolated git worktree on its own branch, and the harness is what decides whether an attempt counted. It is Python and the standard library with nothing else in it, 867 tests, and a CI matrix that runs all of them on Windows, Linux and macOS.

The two facts a harness can observe cheaply are that HEAD moved and that the gate is green, and neither one means anything. A commit made with the allow-empty flag moves HEAD, and the gate was proven green before the task started, so an agent that did nothing at all produces both. Every check after those two exists because that is not hypothetical: an agent that did nothing passed the whole verification surface, and the run reported the backlog complete.

The loop model has write and shell access inside the repo it is working on, and the harness's own control directory is invisible to every diff-based guard, so the harness has to defend its controls from the thing it is running. Setting the gate to an empty list would make every check pass. So the config is sealed by digest at launch and re-verified at every task boundary, and the state, the lock and the stop sentinel live outside the repo entirely.

The backlog gets the same treatment, because it is the harness's worklist rather than part of any task. An attempt that edits it is rejected and the file restored, and the harness ticks the box itself. The one escape hatch, a title tag that lets a task legitimately edit tests, is anchored to the end of the line: an earlier version matched the tag anywhere in the title, so a task could mention it in passing and switch the guard off for every task after it.

The gate is not re-run after the harness amends the ticked checkbox in, so the commit that actually lands is the one thing never verified in its final form. The test-count ratchet fails open: if its probe times out it returns nothing and that check is silently skipped for the attempt. There is no denylist on destructive shell commands, which is an accepted risk rather than an oversight, and it is written down as one. And parallel lanes get their own worktree and their own branch but not their own files, so two lanes editing the same code collide at merge time, and nothing in the harness merges.