Add selective pipeline stage retry

[anishharness]

Summary

• Add docs-backed retry_stages pipeline execution action that reuses original input YAML and supports explicit or derived retry stages.
• Add fallback from matrix/child retry stage IDs to parent retry targets with runAllStages=true when Harness rejects child IDs.
• Restore the confirmation guardrail for selective retry while keeping the new retry functionality.

Test plan

• pnpm test -- tests/tools/tool-handlers.test.ts
• pnpm typecheck

Made with Cursor