Exit 124 reached the string-signature branch before the timeout fail-open,
so a slow probe whose partial output happened to quote 'permission denied'
classified as MODEL_UNUSABLE_INSTALL — a deterministic-broken verdict from
a transient condition. 124 is now excluded from the signature branch, and
the detect/display greps share one hoisted _BROKEN_SIG regex (they had
already drifted: display dropped 'not executable').
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>