Execute and publish planning pull request phases

[rochecompaan]

Part of #180.

Blocked by: #185, #186, #187

Goal

Run specification and plan phases in isolated workspaces, publish their pull requests, and reconcile remote state safely.

Scope

• Run spec and plan agents inside the phase workspace.
• Validate artifacts before committing and pushing them.
• Create planning pull requests with durable side-effect checkpoints.
• Adopt one exact existing pull request after interruption.
• Distinguish review pending, merged, closed-unmerged, missing, and ambiguous states.
• Verify merged artifacts and merge commits on the saved base branch.

Out of scope

• Top-level run-once selection and locking.
• Implementation pull request enforcement.
• Compatibility migration and user documentation.

Acceptance criteria

• Every remote side effect has a durable checkpoint and recovery test.
• Planning pull request bodies contain an exact ownership marker.
• Human edits in merged planning pull requests are preserved.
• Non-not-found host failures stop without changing phase state.
• Closed-unmerged and ambiguous pull requests block advancement.

[rochecompaan]

This was generated by AI during triage.

Triage Notes

This issue is clear and suitable for agent implementation, but its publication workflow depends on the planning pull request adapters and durable planning workspace/state work tracked in the open issues below.

Blocked by: #185, #186, #187

Re-evaluate for agent-ready after all three blockers close.