pin gemma-4 model revisions (upstream 12B template regression: thought channel -> empty generations)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

LESSONS.md

@@ -76,3 +76,13 @@ reproduction: [`RESULTS.md`](RESULTS.md). Everything on `google/gemma-4-E2B-it`
 3. **Verify with the lens, gate with the labels**: the J-lens picks the band,
    measures whether loops compute, and diagnoses failures; STaR difficulty
    labels supervise both the curriculum and (next) the adaptive-depth gate.
+
+## 12. Pin model revisions on fresh nodes
+Upstream updated google/gemma-4-12B-it mid-project: the new chat template
+adds a `<|channel>thought` scaffold, and greedy generation closes the empty
+thought channel and stops — every generation decodes to "". Symptom:
+0/500 pass rates with rc=0 (looks like a harness bug, is a silent model
+swap). E2B was unaffected. Fix: `hf download --revision <hash>` + repoint
+`refs/main` in the cache; node_setup.sh now pins both models (12B
+0e2b1058…, E2B 9dbdf8a8…). Rule: any cross-node result assumes identical
+model revisions — pin them, don't trust "main".

scripts/node_setup.sh

@@ -10,11 +10,16 @@ rclone copy jspace:jspace/results-loop /dev/shm/jspace/results-loop/ --include "
 export HF_HUB_ENABLE_HF_TRANSFER=1
 # downloads can hang mid-transfer on some vast.ai networks (xet stall):
 # retry loop, resume is free
-for m in google/gemma-4-12B-it google/gemma-4-E2B-it; do
+# PIN revisions: upstream updated gemma-4-12B-it's chat template (added a
+# thought channel) mid-project; unpinned downloads silently change behavior.
+for spec in "google/gemma-4-12B-it 0e2b1058541244490925fbacf8972041435691ac" \
+            "google/gemma-4-E2B-it 9dbdf8a839e4e9e0eb56ed80cc8886661d3817cf"; do
+  set -- $spec
   for i in 1 2 3 4 5; do
-    timeout 900 hf download "$m" && break
-    echo "RETRY $i: $m"; sleep 5
+    timeout 900 hf download "$1" --revision "$2" && break
+    echo "RETRY $i: $1"; sleep 5
   done
+  echo "$2" > "$HF_HOME/hub/models--${1//\//--}/refs/main"
 done
 # probe gate: one verified generation before anything batch
 export HF_HUB_OFFLINE=1 JLENS_MODEL=google/gemma-4-12B-it