Add Linear Channel

Adds Linear support via the Chat SDK bridge. The agent participates in issue comment threads. Every comment on a Linear issue triggers the agent — no @-mention needed. NanoClaw doesn't ship channels in trunk — this skill copies the Linear adapter in from the channels branch.

The mechanical steps under Apply carry nc: directive fences: an agent reads the prose and applies them, and a parser can apply them deterministically from the same document. Every directive is idempotent, so the whole skill is safe to re-run; anything a parser can't apply falls back to the prose beside it.

Prerequisites

Recommended: Create a Linear OAuth application so the agent posts as an app identity, not as you. This prevents the adapter from filtering your own comments as self-messages.