fix(agents): protect interactive REPL from external termination

docs/ops/distributed-prefill-kv-network.md

@@ -339,6 +339,8 @@ model's EOS. `--max-response-tokens` defaults to 512 as an explicit safety cap;
 reaching it marks the stage incomplete instead of presenting a truncated answer
 as successful. The Critic receives the Generator completion status and must not
 penalize an honest statement that an open problem has no accepted proof.
+The REPL ignores external `SIGTERM`; its shell supervisor restarts signal-based
+exits. Only `/quit`, `/exit`, or EOF is treated as approval to stop.
 
 ## Rollback
 

scripts/agent_gan_repl.py

@@ -5,6 +5,7 @@
 import argparse
 import hashlib
 import json
+import signal
 import time
 import uuid
 from pathlib import Path
@@ -19,6 +20,17 @@
 )
 
 
+def install_signal_protection() -> None:
+    def ignore_sigterm(signum, _frame):
+        print(
+            f"\n[protected] ignored external signal {signum}. "
+            "Type /quit to approve shutdown.",
+            flush=True,
+        )
+
+    signal.signal(signal.SIGTERM, ignore_sigterm)
+
+
 class TokenPrinter:
     def __init__(self, tokenizer, label: str) -> None:
         self.tokenizer = tokenizer
@@ -56,6 +68,7 @@ def _stage(name: str, warm: dict, actual: dict, text: str) -> dict:
 
 
 def main() -> int:
+    install_signal_protection()
     parser = argparse.ArgumentParser()
     parser.add_argument("--worker-ssh", default="allens")
     parser.add_argument("--address", default="127.0.0.1:51051")

scripts/run_agent_gan_repl.sh

@@ -5,7 +5,23 @@ REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
 PYTHON="${KAKEYA_BENCH_PYTHON:-$HOME/.venv-distwan/bin/python}"
 MODEL="${KAKEYA_BENCH_MODEL:-$HOME/kakeya-models/gemma-4-26B-A4B-it-mlx-4bit}"
 
-exec env PYTHONPATH="$REPO_ROOT:$REPO_ROOT/sdks/python" \
-  "$PYTHON" "$REPO_ROOT/scripts/agent_gan_repl.py" \
-  --tokenizer-id "$MODEL" \
-  "$@"
+trap 'echo "[supervisor] external termination ignored; use /quit"' TERM HUP
+
+while true; do
+  set +e
+  env PYTHONPATH="$REPO_ROOT:$REPO_ROOT/sdks/python" \
+    "$PYTHON" "$REPO_ROOT/scripts/agent_gan_repl.py" \
+    --tokenizer-id "$MODEL" \
+    "$@"
+  status=$?
+  set -e
+  if [[ "$status" -eq 0 ]]; then
+    exit 0
+  fi
+  if [[ "$status" -eq 129 || "$status" -eq 137 || "$status" -eq 143 ]]; then
+    echo "[supervisor] REPL exited from signal ($status); restarting in 2s..."
+    sleep 2
+    continue
+  fi
+  exit "$status"
+done

tests/inference_engine/bridge/test_agent_gan_repl.py

@@ -1,4 +1,7 @@
-from scripts.agent_gan_repl import TokenPrinter, _stage
+import signal
+from pathlib import Path
+
+from scripts.agent_gan_repl import TokenPrinter, _stage, install_signal_protection
 
 
 class Tokenizer:
@@ -51,3 +54,28 @@ def test_repl_stage_is_redacted_and_passes_cache_gate():
         {**actual, "complete": False, "stop_reason": "client_safety_limit"},
         "cut off",
     )["ok"]
+
+
+def test_external_sigterm_is_ignored_until_user_quits(monkeypatch, capsys):
+    installed = {}
+    monkeypatch.setattr(
+        signal,
+        "signal",
+        lambda number, handler: installed.update({number: handler}),
+    )
+    install_signal_protection()
+    installed[signal.SIGTERM](signal.SIGTERM, None)
+    output = capsys.readouterr().out
+    assert "ignored external signal" in output
+    assert "Type /quit to approve shutdown" in output
+
+
+def test_shell_supervisor_restarts_signal_exits_only():
+    source = (
+        Path(__file__).resolve().parents[3]
+        / "scripts"
+        / "run_agent_gan_repl.sh"
+    ).read_text()
+    assert "trap" in source and "TERM HUP" in source
+    assert '"$status" -eq 143' in source
+    assert "restarting in 2s" in source