#3513 issue-lifecycle: an approved plan cannot be sent back to planning

Description

Once a plan is approved in the @swamp/issue-lifecycle model, there is no way to move the lifecycle back to planning. If, after approval, it turns out the plan is wrong or incomplete (new information, a reviewer asks for changes, implementation reveals a flaw before any code lands), the only way out of approved is forward (implement) or a full restart (start), which goes back to triage and discards the plan-iteration context.

The transition table in extensions/models/_lib/schemas.ts (TRANSITIONS) has:

• iterate: ["plan_generated"]
• approve: ["plan_generated"]
• adversarial_review: ["plan_generated"]
• resolve_findings: ["plan_generated", "approved"]
• implement: ["approved", "pr_failed"]

Nothing accepts approved and returns the phase to plan_generated, so iterate is refused by the valid-transition check as soon as the plan is approved.

approve also moves the swamp-club issue status to in_progress, and swamp-club has no backward status transitions, so any fix needs to decide what the Lab status should be when an approved plan is reopened.

Steps to Reproduce

1. Run the issue lifecycle on an issue through triage → plan → approve.
2. Decide the plan needs changes and try iterate with feedback.
3. The method is refused: iterate is only allowed from plan_generated, and the lifecycle is in approved.

Expected

An approved plan can be sent back to planning (e.g. iterate allowed from approved, or a dedicated unapprove/reopen_plan method), returning the phase to plan_generated while keeping the existing plan, its version history, and review findings, so the plan can be revised and re-approved.

Actual

The lifecycle is stuck in approved; the only options are implementing the approved plan or restarting the whole lifecycle from triage.

Environment

• swamp repo, extensions/models/issue_lifecycle.ts
• swamp 20261015.155234.0-sha.fd2cc7ca