Preserve darrow-ticket-pipeline under the Python + uv rollout #188

Parent: #168

Outcome

Preserve darrow-ticket-pipeline as a faithful deprecated benchmark reference under the final Python + uv rollout, choosing migration only where it improves platform support without changing the baseline being measured.

Priority

14 of 14 remaining plugins. It is deliberately deprecated and must not consume migration capacity before supported capabilities and orchestration are complete.

Scope

Audit bin/ticket-pipeline, its tests, and benchmark fixtures after darrow-adaptive-delivery migration. Keep the plugin frozen as a reference; do not revive it as the preferred delivery path or general runtime.

Done criteria

• Decide from benchmark fidelity whether to migrate the existing facade or record an explicit retained POSIX compatibility boundary.
• If migrated, preserve every phase/result record, recovery/refinement behavior, exit code, and benchmark-observable behavior with matched evidence.
• Do not add new orchestration features, queues, daemons, or capabilities.
• If Python is introduced, use a contained locked package and satisfy every Establish and enforce repository-wide Python quality standards #172 quality gate; otherwise document the justified exception.
• Validate the retained reference on its declared platforms and keep comparative eval/benchmark fixtures reproducible.
• Update the deprecated README/spec language and matching manifest versions without changing its status.

Migration blueprint

Use the implementation merged in PR #173 as the default blueprint for Python + uv plugin mechanics. Reuse its self-contained package layout, committed uv lock, runtime/development dependency separation, python-packages.txt inventory, Ruff and strict mypy gates, separate 95% line and branch coverage gates, and fresh copied-artifact validation. Extend that pattern with native-Windows fresh-artifact validation where this rollout requires Windows support. Document any plugin-specific deviation explicitly instead of introducing a competing convention.