Add netem smoke fixture for benchmark simulation

test/bench-network/Dockerfile.netem

@@ -0,0 +1,8 @@
+FROM alpine:3.22
+
+RUN apk add --no-cache iproute2
+
+COPY test/bench-network/netem-smoke.sh /usr/local/bin/livesync-netem-smoke
+RUN chmod +x /usr/local/bin/livesync-netem-smoke
+
+CMD ["livesync-netem-smoke"]

test/bench-network/README.md

@@ -106,3 +106,27 @@ docker compose -f test/bench-network/compose.yml run --rm bench-runner
 This sweep is useful for finding where the remote CouchDB path falls behind the
 local direct P2P path in the current HTTP-proxy latency model. It should not be
 presented as a full smartphone/VPN model.
+
+## Network emulation smoke
+
+The optional `netem` profile checks whether a Linux runner can apply traffic
+shaping inside a Compose-managed container. This is a fixture smoke test for a
+second-tier simulation design; it does not produce synchronisation performance
+results by itself.
+
+```bash
+docker compose -f test/bench-network/compose.yml --profile netem run --rm netem-smoke
+```
+
+The smoke writes `tc qdisc`, route, and interface details under
+`test/bench-network/bench-results/`. Profile parameters can be overridden:
+
+```bash
+NETEM_PROFILE=tethering-vpn \
+NETEM_DELAY_MS=140 \
+NETEM_JITTER_MS=50 \
+NETEM_LOSS_PERCENT=1.0 \
+NETEM_BANDWIDTH_MBIT=10 \
+NETEM_MTU=1380 \
+docker compose -f test/bench-network/compose.yml --profile netem run --rm netem-smoke
+```

test/bench-network/compose.yml

@@ -97,3 +97,23 @@ services:
       BENCH_LIVESYNC_TEST_TEE: ${BENCH_LIVESYNC_TEST_TEE:-0}
     volumes:
       - ./bench-results:/workspace/src/apps/cli/testdeno/bench-results
+
+  netem-smoke:
+    build:
+      context: ../..
+      dockerfile: test/bench-network/Dockerfile.netem
+    profiles:
+      - netem
+    cap_add:
+      - NET_ADMIN
+    environment:
+      NETEM_PROFILE: ${NETEM_PROFILE:-home-wifi}
+      NETEM_INTERFACE: ${NETEM_INTERFACE:-eth0}
+      NETEM_DELAY_MS: ${NETEM_DELAY_MS:-20}
+      NETEM_JITTER_MS: ${NETEM_JITTER_MS:-5}
+      NETEM_LOSS_PERCENT: ${NETEM_LOSS_PERCENT:-0.1}
+      NETEM_BANDWIDTH_MBIT: ${NETEM_BANDWIDTH_MBIT:-100}
+      NETEM_MTU: ${NETEM_MTU:-1500}
+      NETEM_RESULT_ROOT: /bench-results
+    volumes:
+      - ./bench-results:/bench-results

test/bench-network/netem-smoke.sh

@@ -0,0 +1,71 @@
+#!/usr/bin/env sh
+set -eu
+
+profile="${NETEM_PROFILE:-home-wifi}"
+iface="${NETEM_INTERFACE:-eth0}"
+delay_ms="${NETEM_DELAY_MS:-20}"
+jitter_ms="${NETEM_JITTER_MS:-5}"
+loss_percent="${NETEM_LOSS_PERCENT:-0.1}"
+bandwidth_mbit="${NETEM_BANDWIDTH_MBIT:-100}"
+mtu="${NETEM_MTU:-1500}"
+out_root="${NETEM_RESULT_ROOT:-/bench-results}"
+timestamp="$(date -u +%Y%m%d-%H%M%S)"
+out_dir="${out_root}/netem-smoke-${timestamp}"
+out_file="${out_dir}/summary.json"
+
+mkdir -p "$out_dir"
+
+if ! ip link show "$iface" >/dev/null 2>&1; then
+    echo "Network interface '$iface' was not found" >&2
+    ip addr >&2
+    exit 2
+fi
+
+ip link set dev "$iface" mtu "$mtu"
+tc qdisc del dev "$iface" root >/dev/null 2>&1 || true
+tc qdisc add dev "$iface" root netem \
+    delay "${delay_ms}ms" "${jitter_ms}ms" \
+    loss "${loss_percent}%" \
+    rate "${bandwidth_mbit}mbit"
+
+json_lines() {
+    awk '
+        {
+            gsub(/\\/, "\\\\");
+            gsub(/"/, "\\\"");
+            printf "%s    \"%s\"", (NR == 1 ? "" : ",\n"), $0;
+        }
+    '
+}
+
+ip_addr="$(ip addr show "$iface" | json_lines)"
+ip_route="$(ip route | json_lines)"
+tc_qdisc="$(tc qdisc show dev "$iface" | json_lines)"
+
+cat > "$out_file" <<EOF
+{
+  "simulationTier": 2,
+  "mode": "netem-smoke",
+  "profile": "$profile",
+  "interface": "$iface",
+  "netem": {
+    "delayMs": $delay_ms,
+    "jitterMs": $jitter_ms,
+    "lossPercent": $loss_percent,
+    "bandwidthMbit": $bandwidth_mbit,
+    "mtu": $mtu
+  },
+  "ipAddr": [
+$ip_addr
+  ],
+  "ipRoute": [
+$ip_route
+  ],
+  "tcQdisc": [
+$tc_qdisc
+  ]
+}
+EOF
+
+cat "$out_file"
+echo "[netem-smoke] result file: $out_file"