cairn: Skill for Claude Code

Scope one loop unit

Loaded by cairn-dev loop mode at its Scope step. Inputs: the selected unit (slug or finding code), its resolved node, its validated todo body when it has one, and the bound $CAIRN.

Declared exits, exactly one, as the last line you return to loop mode:

• SCOPED: a success criterion is written and implementation may begin.
• REROUTED: a prerequisite must land first; the tracker edits you made ARE this iteration, and loop mode goes straight to Land.
• LOOP HALTED: the unit cannot be scoped without a maintainer.

1. Orient

$CAIRN neighbourhood <node> --include-todos --include-changes
$CAIRN rationale <node>
$CAIRN deps <node> --direction in --transitive

Read all three before deciding anything. The first shows what already claims this area, including an active change you must not collide with. The second is the accepted authority over the node. The third is the blast radius.

If the unit has a todo body, its Scope, Depends on, and Acceptance sections bind here. Where the body and your orientation disagree, the body is the contract and the disagreement is worth reporting in the summary.

2. Respect accepted decisions

An accepted decision covering the node constrains the implementation. You may not contradict one inside this iteration. If the unit cannot be done without contradicting an accepted decision, that is not a coding problem:

• If the superseding decision is knowable, the gap IS the unit. Investigate, stress-test two to four options, persist a justified recommendation as a meta/ artefact, create a blocked tracker item, and return REROUTED so the package lands.
• If it needs a ruling only the maintainer can give, do the same and say so plainly in the artefact. Never self-ratify a binding decision. A local-tier decision may be accepted only through the receipt protocol: two independent lens receipts bound to the subject hash and a ratified_by: machine marker when the loop signs (todo.decision-ratification-tiers).