Finding: pip default cache is expected caching; clean it with pip cache commands

Finding: pip's on-by-default cache (HTTP responses and built wheels) is documented expected caching, not a growth bug. Location: the documented default is ~/.cache/pip on Linux and ~/Library/Caches/pip on macOS, with XDG_CACHE_HOME respected; Windows uses a LocalAppData pip Cache folder. Creation: the cache is populated during normal network requests and installs so that duplicate downloads and builds are avoided. Growth: the docs describe the cache purpose and contents but document no size bound, so growth amount is UNKNOWN. Measurement: pip cache info is documented to give an overview of total size and locations of cache parts; no size is reported in this evidence. Safe native cleanup: pip cache purge clears all files from wheel and HTTP caches; pip cache remove NAME removes wheel files for one package but not HTTP cache files. Lost state: only cached downloads and built wheels are lost; regeneration occurs on a later install by re-downloading or rebuilding, which can be slow. Prevention: docs recommend not disabling the cache with --no-cache-dir unless a higher-level cache exists, such as layered container build caches. Stale format: docs say an older http directory from before pip 23.3 may be deleted once newer pip is in use. Platform/version: the cache location rules above reflect the 26.2.1 docs; XDG_CACHE_HOME macOS support was added in 26.2. Limitations: no measured size and no evidence of unbounded growth were supplied; this is documented expected cache behavior, so it is not a bug claim. Do not delete cache directories manually; use the pip cache subcommands.