Phase 8: Production deployment (Debian 13, Nginx Proxy Manager)

Deployment artifacts for the two-server architecture from ARCHITECTURE.md
§9, grounded in verified Debian 13 (trixie) package facts (Python 3.13,
PostgreSQL 17, Node.js 20, redis-server 8.0, certbot 4.0, ufw --
confirmed rather than guessed) rather than a generic "modern Linux" guide:
deploy/systemd/chatapp.service, deploy/chatapp.env.example,
deploy/backup-postgres.sh, deploy/upgrade.sh, and DEPLOYMENT.md as the
actual numbered runbook.

Revised mid-implementation once the user clarified the app sits behind an
existing, separate Nginx Proxy Manager rather than local Nginx+certbot:
dropped the local Nginx config entirely, gunicorn now binds a TCP port
instead of a Unix socket, and app/main.py gained a static-file mount + SPA
fallback route so gunicorn alone serves the built frontend, /api, and /ws
on one port -- what lets NPM's simple one-upstream-per-domain mode work
with zero custom path routing. Path-traversal-guarded (full_path comes
straight from the URL) and cache-header-differentiated (far-future
immutable on Vite's content-hashed assets, no-cache on index.html/sw.js/
manifest so a deploy actually propagates instead of leaving clients on a
stale service worker) -- verified locally against a real gunicorn process
serving a real frontend build, not just eyeballed.

Two real gaps found and fixed alongside the docs, not just noted: gunicorn
wasn't a dependency anywhere despite being the whole app-server design, and
there was no WebSocket reconnect logic on the client -- a reverse proxy's
idle-connection timeout (NPM's or otherwise) would have silently killed a
quiet chat connection with nothing to recover it. Added exponential-backoff
reconnect to useChatSocket.ts, verified by hand (killed and restarted the
local dev backend mid-session, confirmed auto-reconnect and that a message
sends successfully afterward with no page reload).

Every command in DEPLOYMENT.md that could be verified locally, was: the
exact systemd ExecStart line run against local dev Postgres/Redis with
clean SIGTERM shutdown, the static-file serving behavior against a real
build, both shell scripts syntax-checked. What couldn't be verified from
this sandbox (actual Debian 13 hardware, Nginx Proxy Manager itself) is
flagged explicitly in the plan rather than claimed.

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

deploy/upgrade.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+# Day-2 deploy/upgrade script for the KeepItTalking app server. Run by hand
+# over SSH as the `chatapp` user (or via sudo -u chatapp):
+#
+#   sudo -u chatapp /srv/chatapp/deploy/upgrade.sh
+#
+# Fails loudly and stops before touching the running service if any step
+# fails -- the previous deploy keeps running rather than being torn down
+# mid-upgrade. See ../DEPLOYMENT.md for what each step assumes is already
+# in place (venv, /etc/chatapp/env, the systemd unit, Node.js).
+
+set -euo pipefail
+
+REPO_DIR="/srv/chatapp"
+BACKEND_DIR="${REPO_DIR}/backend"
+FRONTEND_DIR="${REPO_DIR}/frontend"
+ENV_FILE="/etc/chatapp/env"
+
+echo "==> Pulling latest code"
+cd "$REPO_DIR"
+git pull --ff-only
+
+echo "==> Installing backend dependencies"
+cd "$BACKEND_DIR"
+.venv/bin/pip install -e . --quiet
+
+echo "==> Running database migrations"
+# alembic reads DATABASE_URL from the environment (backend/alembic/env.py),
+# so the env file has to actually be sourced into this shell first -- it's
+# not read automatically just because systemd's EnvironmentFile= points at
+# it (that only applies to the chatapp.service process, not this script).
+set -a
+# shellcheck disable=SC1090
+source "$ENV_FILE"
+set +a
+.venv/bin/alembic upgrade head
+
+echo "==> Building frontend"
+cd "$FRONTEND_DIR"
+npm ci --silent
+npm run build --silent
+
+echo "==> Restarting chatapp"
+# Active WebSocket connections drop here and reconnect automatically within
+# a few seconds (frontend/src/ws/useChatSocket.ts's exponential-backoff
+# reconnect) -- expected, not a bug, and not worth a blue-green setup for.
+sudo systemctl restart chatapp
+
+echo "==> Verifying"
+sleep 2
+if curl -sf http://127.0.0.1:8000/api/health >/dev/null; then
+  echo "Health check OK"
+else
+  echo "Health check FAILED -- check: sudo journalctl -u chatapp -n 50" >&2
+  exit 1
+fi
+sudo systemctl status chatapp --no-pager -l | head -10
+
+echo "==> Done. journalctl -u chatapp -f to watch logs."