Custom process: Issue-branch worktree, Claim and Delivery #1388

Parent

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

What to build

A Process can declare one worktree with kind = "issue-branch", and the delivery catalogue Step. The Issue branch is created and named as a Ticket run's (Continuation rules unchanged). The issue holds a Claim from start to end. delivery is the existing Delivery: publish, the Repair loop, and a pull request left ready for review. Validation refuses anything that would lose work: an Issue-branch worktree when no issue is given, or with no delivery after the last Step that uses it. A failed Process keeps its Issue-branch work, as a Failed ticket run does, and names it in the failure.

Acceptance criteria

• A Process with an Issue-branch worktree, two session Steps and delivery ends with a ready-for-review pull request from the Issue branch, and the Claim is removed.
• The issue carries the Claim while the Process runs.
• Starting it without an issue, or with no delivery after the editing Steps, is refused before any session, naming the rule and line.
• A Step that fails before Delivery leaves the work kept, and the failure says where, as for a Failed ticket run.
• Delivery's Repairs run on the Command's Harness, Model and Effort.
• docs/guide.md covers Issue-branch Processes.