Per-project agent switching and approval continuation policy

Provenance stamp: This issue was triaged on June 13, 2026 as part of the older-than-two-month GitHub issue triage exercise.

Source issues: #113, #120

## Summary

Agent switching controls should be visible, project-aware, and predictable. Users should not have to repeatedly correct a global agent selection when each repository has its own agent setup. Approval behavior should also support returning to the previous planning agent when that matches the user's workflow.

## What the source issues requested

- #113 requested that agent selection be remembered per repository, shown near the approve button, and validated before submit so users do not approve into a missing or wrong agent.
- #120 requested an option where approving a plan switches to an implementation agent, then returns to the previous planning agent afterward.

## Triage determination

Both issues are about the same approval handoff contract. Recent work made agent selection more visible for OpenCode, but the remaining backlog is about persistence scope and continuation policy across projects and runtimes.

## Acceptance criteria

- Agent switching preference is stored per project or repository, not only as one global setting.
- The approve action clearly shows whether it will switch agents, switch to a specific agent, or avoid switching.
- Invalid or missing target agents are surfaced before approval.
- A supported runtime can opt into "switch back to previous agent after implementation."
- Runtime limitations are documented for OpenCode, Pi, and other providers.
- The old source issues can be closed once the per-project and return-to-agent requirements are tracked here.