Bound WordPress Playground custom archive cache growth

[chubes4]

Problem

WP Codebox/Homeboy sandbox runs have grown ~/.wordpress-playground to 8.2 GiB by retaining hundreds of content-addressed custom-*.zip archives indefinitely.

Observed on the Extra Chill VPS:

• cache total: 8.2G
• ordinary version archives: a handful at roughly 25-62 MiB
• hundreds of unique custom-<hash>.zip files at roughly 30-62 MiB each
• filesystem reached 95% usage after sustained Codebox/Homeboy test activity

packages/runtime-playground/src/playground-cli-runner.ts owns WP_CODEBOX_PLAYGROUND_WORDPRESS_CACHE_DIR, cache validation, and archive locking, but only deletes invalid archives. No size/age/count retention policy exists for valid custom archives.

Expected

• distinguish reusable release archives from ephemeral/content-addressed custom archives
• clean custom archives when no active runtime/lock references them, or enforce bounded age/size/count retention
• never delete active archives or lock holders
• expose diagnose/cleanup evidence with candidate count, bytes, active protection, removed count, and verified bytes reclaimed
• use the configured WP Codebox cache directory rather than requiring operator cron against a hard-coded home path
• cover concurrent runtimes sharing an archive and stale custom cache accumulation

Acceptance

A workload generating many distinct custom runtime archives converges to a bounded cache after teardown/retention while stable WordPress release archives remain reusable.