Milestone Runner

Run milestone prompts produced by plan-prompts. The runner coordinates mandatory design reconciliation, dependency-safe execution, verification, CI, review, merge/cleanup, and release preparation.

The runner executes existing prompts; it does not author a new product plan. It may require a docs-only reconciliation PR when the current plan no longer matches repository evidence. It invokes stacked-prs for stack topology and ship-workflow only after a complete release train requires preparation.

Core model

A milestone has two independent gates:

1. Design gate. Before implementation, inspect the authoritative plan/prompt, current codebase, merged predecessor diffs, predecessor verification, CI, and local history. Require DESIGN GO or stop on DESIGN NO-GO.
2. Merge gate. After implementation, require release-aware GO plus external PR, CI, verification, and review evidence.

An ignored history ledger is reconstructible local evidence, not authoritative state. .docs/DEVELOPMENT_PLAN.md and .docs/EXECUTION_PROMPTS.md, merged PRs, CI, and current code remain authoritative.

Every terminal milestone result must print the literal heading NEXT STEPS: followed by concrete, ordered actions: the current milestone action, release-preparation state, and the next runnable milestone. A NO-GO must name remediation and either an independent milestone that can proceed or the reason no milestone can. A prose follow-up or JSON next_steps key is insufficient.