Code review (HIGH): a hardcoded 'timeout 600 agy' fails with rc 127 on stock
macOS (no GNU timeout/gtimeout), silently losing the agy reviewer. Probe for
'timeout'/'gtimeout' via command -v and fall back to agy's native --print-timeout
alone when neither exists (mirrors scripts/base64-scan.sh). External cap (600s)
stays >= --print-timeout (540s) so it only backstops a pre-session stall. Factor
the prompt into _AGY_PROMPT to avoid duplicating the long -p string across both
branches. Update the agy + #687 tests to assert the probe + bound + fallback,
regen the 17 goldens + size baseline, refresh the maintainer-note version stamp
to 1.0.16.
The agy block in /gsd-review overflows the exec arg list (inline "$(cat)"),
has no external timeout (pre-session stall hangs past --print-timeout), no
--model escape hatch for a 404'd pinned model, a generic empty-output stub,
and a stale 'no --model flag' note. These tests pin the corrected shape in
gsd-core/workflows/review.md; they fail on next.
