New top-level stack/ for devops reference. stack-poster.tex (+ built PDF) is an arxiv-style tikzposter mapping the whole system: compute hosts (lith, session-server, oven, dp1-feed), data stores, Cloudflare edge, the Mac fleet, an architecture graph, projects/runtimes, dependency versions + what's outdated, and vendors with a cost column (only the $24/mo lith droplet is documented in-repo; everything else marked needs-input / usage — no invented figures). Builds with `tectonic stack-poster.tex` (or latexmk on neo). session-server-db-upgrade-plan.md captures the redis 4->6 / mongodb 6->7 redo after the bump regressed prod: bind :8889 before loading chat history + make redis connect non-blocking (would have prevented the outage), add pingInterval / backoff reconnect, bump node to >=20.19 for mongodb 7, roll out via the health-gated pipeline. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>