feat: run-cell-exposek recipe (cross-mechanism arm)

Same none/erase/route matrix on the expose-K (M2) env, v_hack still the M1
basis -> tests whether an M1-derived direction suppresses the M2 hardcode hack
with no oracle. Teacher-free (M2 emerges on-policy). steps=60, grad_clip=10 by
default now.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

justfile

@@ -118,6 +118,19 @@ run-cell INTERVENTION SEED REFRESH='0':
         --eval-ablate-every=5 \
         --out-tag=_cell_{{ INTERVENTION }}{{ if REFRESH == "0" { "" } else { "_online" } }}_s{{ SEED }}
 
+# CROSS-MECHANISM cell: same matrix but on the expose-K env (M2 = hardcode the
+# visible tests). v_hack is STILL the M1 (run_tests) basis -- the no-oracle
+# generalization test: does an M1-derived direction suppress M2? Teacher-free
+# (M2 emerges on-policy: 64.6% on base in T0), so no pool / no mix. Defaults:
+# steps=60, grad_clip=10. Logs ..._exposek_{intervention}_s{seed}.log.
+run-cell-exposek INTERVENTION SEED K='2':
+    {{ TRAIN }} fast --intervention={{ INTERVENTION }} \
+        --expose-k={{ K }} \
+        --v-hack-path=out/vhack/v_hack_21pairs.safetensors \
+        --seed={{ SEED }} \
+        --eval-ablate-every=5 \
+        --out-tag=_exposek_{{ INTERVENTION }}_s{{ SEED }}
+
 # Regenerate both dynamics plots from the cell logs (default: all cells; pass a
 # narrower glob like 'logs/*_cell_*_s41.log' for the seed-41-only checkpoint).
 regen-dynamics GLOB='logs/*_cell_*.log':