feat: federated learning demo on the actor framework

- supervisor: ignore stale death messages (OneForAll restart storm),
  drop normally-exited children instead of respawning, add a
  restart-rate limit
- register actors before their thread starts so UUID dispatch and
  getSelf cannot race the spawn
- killActor now kills the thread so links see Killed
- fulfill connection promises with the pool winner on simultaneous
  connects
- clamp the PaySim test split on small datasets and split shared
  transaction types across trainers in non-IID partitioning

scripts/demo-p2p.sh

@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+#
+# Demo: federated learning in P2P mode (full mesh, no central coordinator).
+# Starts N peer nodes as separate processes; each trains locally, gossips
+# updates via PeerSync (CRDT-gated rounds), and aggregates independently.
+# At the end every peer must hold the SAME model — the script verifies the
+# saved model files are byte-identical.
+#
+# Usage:
+#   scripts/demo-p2p.sh [ROUNDS] [PEERS] [EPOCHS] [/path/to/paysim.csv]
+#
+# Without a CSV path, nodes fall back to synthetic data (fast; the metrics are
+# meaningless, but the gossip protocol and aggregation are fully exercised).
+set -euo pipefail
+
+ROUNDS="${1:-3}"
+PEERS="${2:-3}"
+EPOCHS="${3:-2}"
+DATA="${4:-}"
+
+BASE_PORT=9600
+OUT="demo-out/p2p"
+
+cd "$(dirname "$0")/.."
+echo "==> Building..."
+cabal build exe:fl-actors >/dev/null
+BIN="$(cabal list-bin fl-actors)"
+
+mkdir -p "$OUT"
+rm -f "$OUT"/*.log fl_model_peer-*.bin
+
+DATA_ARGS=()
+[ -n "$DATA" ] && DATA_ARGS=(--data "$DATA")
+
+PIDS=()
+cleanup() { kill "${PIDS[@]}" 2>/dev/null || true; wait 2>/dev/null || true; }
+trap cleanup EXIT INT TERM
+
+for i in $(seq 0 $((PEERS - 1))); do
+  PORT=$((BASE_PORT + i))
+  ARGS=(--mode p2p --role peer --id "$i" --port "$PORT"
+        --rounds "$ROUNDS" --trainers "$PEERS" --epochs "$EPOCHS")
+  for j in $(seq 0 $((PEERS - 1))); do
+    [ "$j" = "$i" ] && continue
+    ARGS+=(--peer "localhost:$((BASE_PORT + j))")
+  done
+  echo "==> Starting peer-$i on port $PORT"
+  "$BIN" "${ARGS[@]}" "${DATA_ARGS[@]}" > "$OUT/peer$i.log" 2>&1 &
+  PIDS+=($!)
+done
+
+echo "==> Federation running; waiting for all $PEERS peers to finish..."
+echo "    (live log: tail -f $OUT/peer0.log)"
+FAIL=0
+for pid in "${PIDS[@]}"; do
+  wait "$pid" || FAIL=1
+done
+PIDS=()
+if [ "$FAIL" -ne 0 ]; then
+  echo "!!  A peer exited abnormally; check $OUT/ logs"
+  exit 1
+fi
+
+echo
+echo "==> Evaluation results (peer-0's view):"
+grep "Eval round=" "$OUT/peer0.log" || true
+echo
+
+MODELS=(fl_model_peer-*.bin)
+if [ "${#MODELS[@]}" -ne "$PEERS" ]; then
+  echo "!!  Expected $PEERS model files, found ${#MODELS[@]}; check $OUT/ logs"
+  exit 1
+fi
+
+FIRST="${MODELS[0]}"
+for m in "${MODELS[@]:1}"; do
+  if ! cmp -s "$FIRST" "$m"; then
+    echo "!!  Divergence: $m differs from $FIRST"
+    md5sum "${MODELS[@]}"
+    exit 1
+  fi
+done
+echo "==> Success: all $PEERS peers converged to a byte-identical model:"
+ls -la "${MODELS[@]}"
+echo "    Full logs in $OUT/"