fix(stress): port harnesses to v1.2 single-session API + remove WS-batch hang

Local API stress (lib.mjs / api_stress.mjs):
- setupSession now does login -> /admin/api/reset and returns sid="main".
  Drops the dead /admin/api/quizzes + /admin/api/sessions calls left over
  from the multi-quiz codex era.
- bootServer writes the fixture pool (STRESS_POOL by default) to a tmp
  file and passes QUIZ_POOL_PATH so the v1.2 server has a session at
  startup.
- happyPath: drop the post-connect lobby_update wait (race with snapshot
  dispatch) and stop double-driving the lifecycle (next() already opens
  the next question, an explicit open() afterwards is a no-op).
- cross_session: rewritten as "cookie not honored on a non-existent sid"
  since v1.2 hosts a single canonical session.

Live accuracy stress (live_accuracy.mjs):
- Per-student lobby-snapshot timeout (12s) with WS error/close rejection,
  so a stalled handshake no longer hangs Promise.all until the outer
  shell timeout (which produced the exit=124 cycles).
- Open all student WSs in parallel (mirrors what real students do); the
  batch-of-8 throttle was masking the question we wanted answered.
- Instructor WS open also bounded by a 15s race so any failure surfaces
  as actionable error text instead of a silent stall.

Bootstrap (deploy/bootstrap.sh):
- Stage 1 provisions a 2GB swap file (idempotent) with vm.swappiness=10.
  1GB-RAM ECS instances OOM-kill uvicorn under WS-burst start-of-class
  pressure; swap absorbs the spike without affecting steady state.
- Pool seeding prefers examples/demo10_pool.json over the 2-question
  example so a fresh deploy boots with a usable demo.

Pool fixture (examples/demo10_pool.json):
- 10-question generic-knowledge demo pool, gitignore exception added.

deploy/bootstrap.sh

@@ -25,14 +25,29 @@ fi
 
 stage() { printf '\n==> Stage %s\n' "$*"; }
 
-stage "1/9: apt update + base packages"
+stage "1/10: provision 2GB swap (skip if /swapfile already present)"
+# 1GB-RAM ECS instances OOM-kill uvicorn during ws-burst peaks (50+
+# simultaneous WS handshakes during class start). 2GB swap absorbs
+# transient pressure without touching steady-state behavior.
+if [ ! -f /swapfile ]; then
+    fallocate -l 2G /swapfile
+    chmod 600 /swapfile
+    mkswap /swapfile >/dev/null
+    swapon /swapfile
+    grep -q '^/swapfile ' /etc/fstab || echo '/swapfile none swap sw 0 0' >> /etc/fstab
+fi
+# vm.swappiness=10 keeps active pages in RAM, only swap under real pressure.
+echo 'vm.swappiness=10' > /etc/sysctl.d/99-quiz.conf
+sysctl -p /etc/sysctl.d/99-quiz.conf >/dev/null
+
+stage "2/10: apt update + base packages"
 apt-get update -q
 DEBIAN_FRONTEND=noninteractive apt-get install -y -q \
     git curl ca-certificates gnupg \
     python3 python3-venv python3-pip \
     debian-keyring debian-archive-keyring apt-transport-https
 
-stage "2/9: install Caddy (skip if present)"
+stage "3/10: install Caddy (skip if present)"
 if ! command -v caddy >/dev/null 2>&1; then
     curl -1sLf 'https://dl.cloudsmith.io/public/caddy/stable/gpg.key' \
         | gpg --dearmor -o /usr/share/keyrings/caddy-stable-archive-keyring.gpg
@@ -42,12 +57,12 @@ if ! command -v caddy >/dev/null 2>&1; then
     apt-get install -y -q caddy
 fi
 
-stage "3/9: create $APP_USER system user (skip if present)"
+stage "4/10: create $APP_USER system user (skip if present)"
 if ! id "$APP_USER" >/dev/null 2>&1; then
     useradd --system --shell /usr/sbin/nologin --home-dir "$APP_DIR" "$APP_USER"
 fi
 
-stage "4/9: clone or update repo into $APP_DIR"
+stage "5/10: clone or update repo into $APP_DIR"
 if [ -d "$APP_DIR/.git" ]; then
     git -C "$APP_DIR" fetch origin
     git -C "$APP_DIR" reset --hard "origin/$BRANCH"
@@ -57,12 +72,12 @@ else
 fi
 chown -R "$APP_USER":"$APP_USER" "$APP_DIR"
 
-stage "5/9: build venv + install dependencies"
+stage "6/10: build venv + install dependencies"
 sudo -u "$APP_USER" -H python3 -m venv "$APP_DIR/.venv"
 sudo -u "$APP_USER" -H "$APP_DIR/.venv/bin/pip" install --quiet --upgrade pip
 sudo -u "$APP_USER" -H "$APP_DIR/.venv/bin/pip" install --quiet -e "$APP_DIR"
 
-stage "6/9: configure environment (.env)"
+stage "7/10: configure environment (.env)"
 ENV_FILE="$APP_DIR/.env"
 if [ ! -f "$ENV_FILE" ]; then
     if [ -f /root/.quiz.env ]; then
@@ -98,21 +113,23 @@ EOF
     chmod 600 "$ENV_FILE"
 fi
 
-stage "7/9: seed pool.json (if not already present)"
+stage "8/10: seed pool.json (if not already present)"
 POOL_FILE="$APP_DIR/pool.json"
 if [ ! -f "$POOL_FILE" ]; then
-    cp "$APP_DIR/examples/pool_example.json" "$POOL_FILE"
+    SEED_POOL="$APP_DIR/examples/demo10_pool.json"
+    [ -f "$SEED_POOL" ] || SEED_POOL="$APP_DIR/examples/pool_example.json"
+    cp "$SEED_POOL" "$POOL_FILE"
     chown "$APP_USER":"$APP_USER" "$POOL_FILE"
-    echo "Seeded $POOL_FILE from examples/pool_example.json — replace with your real pool when ready."
+    echo "Seeded $POOL_FILE from $(basename "$SEED_POOL"). Replace with your real pool when ready."
 fi
 
-stage "8/9: install systemd unit"
+stage "9/10: install systemd unit"
 install -m 644 "$APP_DIR/deploy/quiz.service" /etc/systemd/system/quiz.service
 systemctl daemon-reload
 systemctl enable quiz.service
 systemctl restart quiz.service
 
-stage "9/9: configure Caddy"
+stage "10/10: configure Caddy"
 sed "s/__DOMAIN__/$DOMAIN/g" "$APP_DIR/deploy/Caddyfile.tpl" > /etc/caddy/Caddyfile
 systemctl reload caddy