Current OpenCode and Superpowers compatibility revalidation

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

Source issues: #112, #190, #408, #479

## Summary

Several older issues were filed while the OpenCode integration and planning flow were changing quickly. Some of the original complaints appear to be addressed by newer workflow modes, plan storage changes, and submit-plan changes, but the backlog still needs one place to verify the current behavior and capture any remaining compatibility gaps.

## What the source issues requested

- #112 requested compatibility with Superpowers workflows, including cases where Superpowers writes plans to files instead of using the native plan path.
- #190 reported that starting a new OpenCode session with `/new` could show a diff from the previous session.
- #408 reported that OpenCode plan content could flash briefly, then collapse into only the path to the plan file.
- #479 requested a clearer OpenCode workflow split so Plannotator does not eagerly expose `submit_plan` to the wrong agents or interrupt native planning workflows.

## Triage determination

These should not stay as four stale OpenCode issues. The right next step is a current compatibility pass against the shipped workflow modes and plan-storage behavior. If current releases no longer reproduce the old problems, close the source issues with the replacement issue as the historical record. If something still reproduces, keep the new issue focused on the current failure mode.

## Acceptance criteria

- Verify Superpowers or OpenSpec workflows with current manual, plan-agent, user-managed, and all-agents modes where applicable.
- Verify that `/new` or equivalent OpenCode session reset no longer carries stale plan or diff state into the next session.
- Verify that plan-file submissions render content, not just a path, across supported OpenCode hosts.
- Verify that default OpenCode behavior no longer pushes non-planning agents toward `submit_plan`.
- Document which source issues are fully resolved by current releases and which have current reproduction steps.
- The old source issues can be closed once the current compatibility result is recorded here.