docs: record Synapse 1.157.1 upgrade + add upgrade runbook

Upgraded LXC 151 from 1.156.0 to 1.157.1 (packages.matrix.org, Trixie).

The host was found on 1.156.0 despite this README recording 1.155.0 — an
intermediate upgrade had gone unlogged. Corrected the infra and Tech Stack
tables and noted the drift so future upgrades verify with dpkg rather than
trusting the docs.

Not a security release (no CVEs in range; the last were fixed in 1.152.1),
but 1.157.0 fixes an application-service ephemeral-events regression shipped
in 1.156.0, which affects hookshot. No schema-version bump (94 -> 94) and the
three new background updates completed immediately. Our experimental_features
block (MatrixRTC/Element Call MSCs) is unaffected by 1.157.0's removal of
msc3861, which we do not use; it was preserved via --force-confold.

Also adds a Synapse upgrade runbook — the repo had no documented procedure or
automation for this at all, so the two prior upgrades were done out-of-band.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -50,7 +50,7 @@ matrix/
 
 | Service | IP | LXC | RAM | Disk | Versions |
 |---------|----|-----|-----|------|----------|
-| Synapse | 10.10.10.29 | 151 | 8GB | 50GB | Synapse 1.155.0, LiveKit 1.9.11, hookshot 7.3.2, coturn latest |
+| Synapse | 10.10.10.29 | 151 | 8GB | 50GB | Synapse 1.157.1, LiveKit 1.9.11, hookshot 7.3.2, coturn latest |
 | PostgreSQL 17 | 10.10.10.44 | 109 | 6GB | 30GB | PostgreSQL 17.9 |
 | Cinny Web | 10.10.10.6 | 106 | 2GB | 8GB | Debian 12, nginx, Node 24, Lotus Cinny fork (custom, tracks `cinnyapp/cinny` main) |
 | Draupnir | 10.10.10.24 | 110 | 1GB | 10GB | Draupnir v2.9.0, Node.js v22 |
@@ -573,6 +573,7 @@ Periodic `TLS/TCP socket error: Connection reset by peer` in coturn logs. Normal
 
 ### Quality of Life
 - [x] **Upgrade Synapse to v1.155.0** — Done 2026-06-18. LXC 151 was already on Debian 13 Trixie; no OS migration needed.
+- [x] **Upgrade Synapse to v1.157.1** — Done 2026-07-23. Note: the host was found running **1.156.0**, not the 1.155.0 recorded here — an intermediate upgrade had happened without being logged, so always verify with `dpkg-query -W matrix-synapse-py3` rather than trusting this file. Not a security release (no CVEs between 1.155.0 and 1.157.1; the last advisories were fixed back in 1.152.1), but 1.157.0 fixes an application-service ephemeral-events regression that 1.156.0 shipped — which affects hookshot. No schema-version bump (94 → 94); the three new background updates finished immediately. `experimental_features` (MatrixRTC/Element Call MSCs) was preserved and is unaffected by the v1.157.0 removal of `msc3861`, which we do not use.
 - [x] Migrate from SQLite to PostgreSQL
 
 - [x] TURN/STUN server (coturn) for reliable voice/video
@@ -656,6 +657,63 @@ Periodic `TLS/TCP socket error: Connection reset by peer` in coturn logs. Normal
 
 ---
 
+## Synapse Upgrade Runbook
+
+Synapse is installed from the **matrix.org apt repo** (`matrix-synapse-py3`) on **LXC 151** — it is
+not containerized, and none of the auto-deploy scripts in `deploy/` touch it. Upgrades are manual.
+Access is via the Proxmox host: `ssh compute-storage-01`, then `pct exec 151 -- <cmd>`.
+
+**1. Verify the real current version** — this file has been wrong before:
+```bash
+pct exec 151 -- dpkg-query -W -f='${Version}\n' matrix-synapse-py3
+pct exec 151 -- bash -c 'apt-get update -qq && apt-cache policy matrix-synapse-py3'
+```
+
+**2. Read upstream upgrade notes** for every version in the gap:
+<https://element-hq.github.io/synapse/latest/upgrade.html>. Look for removed config keys, schema
+bumps, and minimum Python/PostgreSQL bumps. Then check ours against them:
+```bash
+pct exec 151 -- grep -nE 'experimental_features|msc[0-9]+|modules:' /etc/matrix-synapse/homeserver.yaml
+pct exec 151 -- python3 -V                       # needs >= 3.10
+pct exec 109 -- su postgres -c 'psql -tAc "select version()"'   # needs >= 14
+```
+
+**3. Confirm a backup exists.** Nightly `vzdump` snapshots *all* guests at 03:00 to `mediafs`
+(`keep-last=2`), plus a weekly run to `pbs`. Both LXC 151 (Synapse) and 109 (PostgreSQL) are
+covered — a rollback needs **both**, since they'd have to be restored to a consistent point:
+```bash
+pvesm list mediafs | grep -E '\-(151|109)\-'
+```
+Take an on-demand backup instead if the nightly one is stale: `vzdump 151 109 --storage mediafs --mode snapshot`.
+Note that Synapse does **not** support downgrading once new code has run against the database —
+treat every upgrade as one-way in practice, regardless of whether the schema version changed.
+
+**4. Upgrade.** `--force-confold` is essential: `homeserver.yaml` is a dpkg conffile and we have
+modified it heavily, so without this apt may prompt or overwrite it.
+```bash
+pct exec 151 -- bash -c 'DEBIAN_FRONTEND=noninteractive apt-get install -y \
+  -o Dpkg::Options::=--force-confold -o Dpkg::Options::=--force-confdef \
+  matrix-synapse-py3=<VERSION>+trixie1'
+```
+The package restarts `matrix-synapse` itself.
+
+**5. Verify:**
+```bash
+pct exec 151 -- systemctl is-active matrix-synapse
+pct exec 151 -- ls /etc/matrix-synapse/*.dpkg-*        # must be empty — config was preserved
+pct exec 151 -- curl -s http://localhost:8008/_matrix/federation/v1/version
+pct exec 151 -- journalctl -u matrix-synapse --since '5 min ago' -p err --no-pager
+```
+Then confirm background updates drain (empty result = done) before any *further* upgrade:
+```bash
+pct exec 109 -- su postgres -c "psql -d synapse -tAc 'select update_name from background_updates'"
+```
+
+**6. Record it** — update the version in the infra table, the Tech Stack table, and the Server
+Checklist in this file.
+
+---
+
 ## Monitoring & Observability
 
 ### Prometheus Scrape Jobs
@@ -786,7 +844,7 @@ All commands use the `!` prefix. Run `!help` in any room for the full list.
 
 | Component | Technology | Version |
 |-----------|-----------|---------|
-| Homeserver | Synapse | 1.155.0 |
+| Homeserver | Synapse | 1.157.1 |
 | Database | PostgreSQL | 17.9 |
 | TURN | coturn | latest |
 | Video/voice calls | LiveKit SFU | 1.9.11 |