remote cache logger - new plugin to help debug the remote cache

[kaplan-shaked]

Summary

Adds a new experimental backend pants.backend.experimental.tools.remote_cache_logger that logs remote cache speculation outcomes to a CSV file.

This is useful for debugging remote cache hit/miss behavior and identifying non-deterministic builds.

Features

• Logs remote_cache_read_speculation workunits with:
  • description - What action was being cached
  • action_digest - The cache key
  • outcome - Whether it was a hit or miss
  • request - Full request details
• Outputs to .pants.d/workdir/<run_id>.csv by default
• Controlled via [remote-cache-logger] options

Usage

pants.toml

[GLOBAL]
backend_packages.add = ["pants.backend.experimental.tools.remote_cache_logger"]

[remote-cache-logger]
enabled = true

[kaplan-shaked]

#21294
based om this PR