Completes #1774. The prior fix redirected the AST cache dir to CWD but
file_hash still called _ensure_stat_index(root) without the cache
location, so the hash fastpath's stat-index.json kept anchoring on the
key-root (the analyzed corpus) — leaving a stray graphify-out/cache/
stat-index.json inside a writable foreign corpus even though the AST
cache itself had moved to CWD.
Thread cache_root through file_hash -> _ensure_stat_index (which already
accepts it, #1747). Surfaced by an out-of-CWD parallel-extract edge case:
the leak was masked in the in-process test suite because _stat_index_root
is a set-once module global that an earlier test had already pinned. The
regression test resets that global to simulate a fresh process and
asserts the corpus stays clean while the stat index lands under CWD.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
safishamsi
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