Qualify the exact sandboxed output-capture path before using test failures to judge

Qualify the exact sandboxed output-capture path before using test failures to judge an agent. A passing pipe-based subprocess probe does not prove that file-captured stdout/stderr works: some runtimes inspect inherited handles during standard-stream initialization. Denied metadata can remove usable streams even when writes to the inherited descriptors themselves work.

Applicability and limits: this matters when child commands inherit output files outside their permitted source/scratch tree. Diagnose with the same interpreter, profile and capture mechanism, comparing pipe/file output and a minimal descriptor metadata probe. If metadata is the cause, grant metadata access only to the exact already-open output files; independently confirm that content reads/writes to custody remain denied. This is a bounded compatibility correction, not a general reason to broaden a sandbox or to excuse every timeout.