Read Action Files or Name the Cause When UV_NO_CACHE Removes the Resolved PyYAML Interpreter #2358

Problem

When in-process PyYAML is missing, the repo gate's composite-actions check resolves a PyYAML interpreter once per run through uvx --with pyyaml python, then runs its reader under that interpreter directly (#2348). Under UV_NO_CACHE=1, or uv's no-cache = true configuration, uv builds that environment in a temporary cache and deletes it when uvx exits, so the resolved interpreter is already gone when the reader launches.

The check then reports one host finding, the interpreter uvx provided could not start: [Errno 2] No such file or directory: '<temporary path>'. The shell half never runs on such a host. The finding names a vanished temporary path rather than the cause or the remedy (unset UV_NO_CACHE, or make PyYAML importable), and scripts/README.md says uvx alone is enough.

Done When

On a host with UV_NO_CACHE set and no in-process PyYAML, either the shell half still reads the action files, for example by falling back to running the reader inside uvx per file on this error, or the single host finding names the no-cache setting and the remedy. A test with a stub probe pins whichever behavior is chosen.

Found by the final strict review pass on #2348, which was at its review-round cap, so the finding was filed rather than fixed.