milestone-runner

# 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 i...