Custom process: Processes on an issue #1385

Parent

#877 (Spec: Custom processes). Design record: docs/grill-with-docs/877-composable-by-file.md, ADR-0024.

What to build

thirdshift process <name> issue <issue> gives the Process an issue: a number or an Issue URL, resolved as thirdshift skill resolves it, origin-mismatch rule included. Every session Step gets the issue from thirdshift as .thirdshift-issue.md in its worktree, with only Trusted account comments, and its Session prompt names the issue. Before each session on the issue, a Resume included, its issue is checked again, as in a Ticket run: an edit by an account that is not a Trusted account fails the Step instead of starting the session.

Acceptance criteria

• An issue number and an Issue URL both work. An Issue URL from another repository stops before any work.
• Each session Step's worktree has .thirdshift-issue.md with the title, the body and only Trusted-account comments.
• An untrusted edit to the issue fails the next Step before its session starts, with the cause in the Command log.
• Command Steps get the issue URL in their environment, if that Ticket has landed. Otherwise this Ticket adds it.