[Feature Request] Plans as first-class, replayable artifacts

[cagdasyurekli]

Problem

Plan mode produces a plan via propose_plan (coworker/tools/plan.py) and then effectively discards it — the plan is ephemeral, tied to the session, and cannot be re-run, shared, or traced back to the audit trail. The project\x27s headline is "finished work, not chat," yet the plan — the roadmap to that work — is not itself a deliverable.

Proposed Solution

1. Persist approved plans as durable artifacts (alongside session artifacts) with a stable reference.
2. Add a "re-run this plan" action that starts a new session from the stored plan.
3. Link the plan artifact to its execution in the audit trail ("this deliverable came from plan X"), so a finished deliverable can be traced back to the plan that produced it.

Implementation Scope & Alignment

• Scope: ~150-200 lines (persistence in conversations.py/artifacts + a plan_replay action + a GUI affordance).
• Zero New Dependencies.
• Alignment: Delivers on the "finished work" promise and strengthens the governance story by making plans durable, replayable, and auditable.