diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9a417bfc5..a6dd84d9d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -69,6 +69,17 @@ jobs:
       - name: Run tests
         run: npm test -- --run
 
+  shell-lint:
+    name: Shell script lint
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: shellcheck deploy scripts
+        # shellcheck ships preinstalled on ubuntu-latest.
+        run: shellcheck api/deploy/backup/*.sh
+
   test-backend:
     name: Backend tests
     runs-on: ubuntu-latest
diff --git a/api/deploy/backup/cercol-db-backup.sh b/api/deploy/backup/cercol-db-backup.sh
new file mode 100755
index 000000000..55baacc07
--- /dev/null
+++ b/api/deploy/backup/cercol-db-backup.sh
@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+# Nightly two-leg backup of the cercol PostgreSQL database.
+# Spec: docs/decisions/0017-database-backups-two-leg.md
+#
+# Leg 1: pg_dump -Fc of the cercol database only, kept on-box under
+#        /var/backups/cercol/ (7 most recent dumps).
+# Leg 2: the same dump, gpg-encrypted (AES256, symmetric), pushed to
+#        Google Drive via rclone (30-day retention on the remote).
+#
+# Runs as root from /etc/cron.d/cercol-db-backup (see that file for the
+# one-time install steps). The dump itself runs as postgres via runuser
+# (peer auth); root owns the passphrase file, the backup directory and
+# the rclone config.
+#
+# Failure contract: exits non-zero on ANY failure, appends a
+# "BACKUP FAILED" line to the log (the cron line redirects output to
+# /home/cercol/logs/db-backup.log) and leaves a FAILED marker file that
+# the next successful run removes. No silent deaths.
+
+set -euo pipefail
+
+BACKUP_DIR="/var/backups/cercol"
+PASSPHRASE_FILE="/root/.cercol-backup-passphrase"
+RCLONE_REMOTE="gdrive:cercol-db-backups"
+LOCAL_KEEP=7
+REMOTE_KEEP_DAYS=30
+LOG_DIR="/home/cercol/logs"
+FAIL_MARKER="$LOG_DIR/db-backup.FAILED"
+
+ts() { date -u +"%Y-%m-%dT%H:%M:%SZ"; }
+
+fail() {
+    echo "$(ts) BACKUP FAILED: $1" >&2
+    mkdir -p "$LOG_DIR"
+    echo "$(ts) $1" > "$FAIL_MARKER"
+    exit 1
+}
+trap 'fail "command on line $LINENO exited non-zero"' ERR
+
+# postgres cannot read root's cwd; avoid the noisy "could not change
+# directory" warning from runuser/pg_dump.
+cd /
+
+[ "$(id -u)" -eq 0 ] || fail "must run as root"
+[ -r "$PASSPHRASE_FILE" ] || fail "passphrase file $PASSPHRASE_FILE missing or unreadable"
+command -v rclone > /dev/null || fail "rclone not installed"
+rclone listremotes | grep -q '^gdrive:$' || fail "rclone remote 'gdrive' not configured"
+
+# Backup dir: root-owned, postgres can read (needed for the restore
+# test in the runbook, which runs pg_restore as postgres).
+install -d -m 0750 -o root -g postgres "$BACKUP_DIR"
+
+stamp=$(date -u +%Y%m%dT%H%M%SZ)
+dump="$BACKUP_DIR/cercol-$stamp.dump"
+
+# Leg 1: local dump. -Fc is already zlib-compressed; no extra gzip.
+runuser -u postgres -- pg_dump -Fc --dbname=cercol > "$dump"
+chown root:postgres "$dump"
+chmod 0640 "$dump"
+[ -s "$dump" ] || fail "dump file is empty"
+
+# Integrity check: a corrupt archive fails to list.
+runuser -u postgres -- pg_restore --list "$dump" > /dev/null
+
+# Local rotation: keep the LOCAL_KEEP most recent dumps. Filenames
+# embed a UTC timestamp (cercol-YYYYMMDDTHHMMSSZ.dump), so reverse
+# lexical order IS reverse chronological order.
+shopt -s nullglob
+printf '%s\n' "$BACKUP_DIR"/cercol-*.dump | sort -r | tail -n +$((LOCAL_KEEP + 1)) | xargs -r rm --
+shopt -u nullglob
+
+# Leg 2: encrypt and push off-box, then drop the local ciphertext.
+gpg --batch --yes --pinentry-mode loopback \
+    --symmetric --cipher-algo AES256 \
+    --passphrase-file "$PASSPHRASE_FILE" \
+    -o "$dump.gpg" "$dump"
+rclone copy "$dump.gpg" "$RCLONE_REMOTE"
+rclone delete --min-age "${REMOTE_KEEP_DAYS}d" "$RCLONE_REMOTE"
+rm -f "$dump.gpg"
+
+rm -f "$FAIL_MARKER"
+echo "$(ts) BACKUP OK: $(basename "$dump") ($(du -h "$dump" | cut -f1)) local, encrypted copy pushed to $RCLONE_REMOTE"
diff --git a/api/deploy/cron/cercol-db-backup b/api/deploy/cron/cercol-db-backup
new file mode 100644
index 000000000..fc67226a6
--- /dev/null
+++ b/api/deploy/cron/cercol-db-backup
@@ -0,0 +1,24 @@
+# Cercol - nightly two-leg backup of the cercol PostgreSQL database.
+# Runs api/deploy/backup/cercol-db-backup.sh as root: local pg_dump
+# rotation plus gpg-encrypted rclone push to Google Drive.
+# Spec: docs/decisions/0017-database-backups-two-leg.md
+#
+# Install: see the "Database backups" section of docs/ops/runbook.md
+# for the full one-time block (passphrase file, rclone OAuth config,
+# log directory, cron install, first run, restore test).
+#
+# Verify after install:
+#   ls -la /etc/cron.d/cercol-db-backup
+#   tail -2 /home/cercol/logs/db-backup.log        # after 03:15 UTC
+#   ls -la /home/cercol/logs/db-backup.FAILED      # must NOT exist
+#
+# Output is redirected to the log file on purpose: the script owns its
+# failure signalling (FAILED marker + non-zero exit), unlike the
+# MAILTO="" pattern of the older crons that swallows errors.
+
+SHELL=/bin/bash
+PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+
+# Daily at 03:15 UTC: offset from the 02:00 crawl parser, the 03:00
+# Sunday Bing ingest and the 04:00 token purge.
+15 3 * * * root /home/cercol/api/api/deploy/backup/cercol-db-backup.sh >> /home/cercol/logs/db-backup.log 2>&1
diff --git a/docs/decisions/0017-database-backups-two-leg.md b/docs/decisions/0017-database-backups-two-leg.md
new file mode 100644
index 000000000..729a6785e
--- /dev/null
+++ b/docs/decisions/0017-database-backups-two-leg.md
@@ -0,0 +1,124 @@
+# ADR 0017: Database backups, two-leg strategy
+
+- **Number**: 0017
+- **Title**: Two-leg backup strategy for the cercol PostgreSQL database
+- **Status**: Accepted
+- **Date**: 2026-07-05 (proposed and accepted same day; design signed
+  off by the operator before implementation)
+
+## Context
+
+The cercol PostgreSQL database (~20 MB) holds everything the project
+cannot regenerate: profiles, auth tables, results (the raw material for
+the Phase 4+ team instrument), witness sessions, groups, blog posts and
+funnel events. Until now it had no logical backup at all: the July 2026
+reliability audit confirmed no `pg_dump` anywhere on the server, and
+`docs/ops/runbook.md` carried the TODO "Backups are the operator's
+responsibility (`pg_dump`). Frequency and offsite copy procedure: TODO
+document." This ADR closes that TODO.
+
+Hetzner Cloud machine-level backups ARE enabled on the VPS (billed as
+"Backup (20% of instance price)" on the invoice): whole-VM,
+crash-consistent, 7-day retention, stored with the same provider under
+the same account. They are the coarse fallback, not a substitute:
+
+- no granular restore (whole-VM rollback also rolls back topquaranta,
+  which shares the box),
+- no off-provider copy (a lost account or provider incident loses both
+  the VM and its backups),
+- crash-consistent only, no application-consistent guarantee for
+  PostgreSQL.
+
+## Decision
+
+Two legs, proportionate to actual risk on a shared VPS:
+
+- **Leg 1, logical-error recovery**: nightly `pg_dump` of the cercol
+  database only (never topquaranta's), custom format (`-Fc`), stored
+  on-box under `/var/backups/cercol/` with local rotation keeping the
+  7 most recent dumps. Covers accidental deletes, bad migrations and
+  application bugs, restorable table by table with `pg_restore`.
+- **Leg 2, disk/box-loss recovery**: the same dump encrypted and pushed
+  off-box to Google Drive via rclone, with its own retention (30 days).
+  Google Drive is chosen because it is free, already in use by the
+  operator, and decoupled from the pending Cloudflare Pages migration
+  (ADR 0013).
+
+Implementation details (resolved during implementation, see
+`api/deploy/backup/cercol-db-backup.sh`):
+
+- **Encryption: gpg symmetric (AES256)** with a passphrase read from a
+  root-only file at `/root/.cercol-backup-passphrase`. gpg 2.2 is
+  already installed on the server; `age` is not, and installing a new
+  tool for one `gpg --symmetric` call fails the proportionality test.
+  The passphrase file is created by the operator at install time and is
+  NEVER committed to the repository.
+- **rclone auth: interactive OAuth token flow (user-owned quota)**, not
+  a service account. On a personal Google account, service-account
+  uploads can land in the service account's own 15 GB quota instead of
+  the user's Drive, and the SA identity would be one more secret to
+  manage. The OAuth token is created interactively by the operator
+  (`rclone config`) during the one-time manual install step; rclone
+  refreshes it automatically afterwards.
+- **Schedule: daily at 03:15 UTC**, offset from the existing crons
+  (02:00 crawl parser, 03:00 Sunday Bing ingest, 04:00 token purge,
+  05:00 daily jobs). Runs as root: the dump itself is executed via
+  `runuser -u postgres` (peer auth), while root owns the passphrase
+  file, the backup directory and the rclone config.
+- **No silent deaths**: the script exits non-zero on any failure, logs
+  every run to `/home/cercol/logs/db-backup.log` (the cron line
+  redirects stdout and stderr there), and maintains a
+  `/home/cercol/logs/db-backup.FAILED` marker file that is written on
+  failure and removed on the next success, so a human or a future
+  digest job can detect a broken backup without reading cron mail.
+  This deliberately breaks with the `MAILTO=""` pattern of the other
+  crons, which has let jobs die silently for weeks, twice.
+
+## Alternatives considered
+
+- **Hetzner Storage Box**: rejected on cost. Hard constraint for this
+  decision: no new spend.
+- **Cloudflare R2**: rejected to avoid coupling the backup path to an
+  incomplete migration (ADR 0013 is still Proposed); if that migration
+  is later accepted, moving Leg 2 to R2 is a one-line rclone remote
+  change.
+- **Backblaze B2**: rejected to avoid a new account and identity to
+  manage for a 20 MB payload.
+- **Committing encrypted dumps to Git**: rejected on security grounds
+  (user PII in a public repository, even encrypted, with no revocation
+  story) and repo hygiene (unbounded binary growth).
+
+## Consequences
+
+- One manual install step on the server, mirroring the existing cron
+  deployment pattern: files live in the repo
+  (`api/deploy/backup/cercol-db-backup.sh`,
+  `api/deploy/cron/cercol-db-backup`), the operator installs once. The
+  exact install block lives in `docs/ops/runbook.md`.
+- Restore procedures (on-box, off-box, and the Hetzner whole-VM last
+  resort) and a quarterly restore test are documented in
+  `docs/ops/runbook.md`, replacing the TODO.
+- Restore capability is only proven by restoring: the runbook documents
+  a scratch-database restore test to run once after install and then
+  quarterly.
+- Follow-up, out of scope here: standardise output redirection and
+  failure alerting across the other existing cron jobs; the current
+  `MAILTO=""` pattern lets crons die silently for weeks (proven twice:
+  crawl-parser since 2026-05-28, and the 2026-04-16 Caddy outage class
+  of silence).
+
+## Related
+
+- `docs/ops/runbook.md` "Database backups" section: install block,
+  restore procedures, quarterly restore test (replaces the old TODO).
+- `api/deploy/backup/cercol-db-backup.sh` and
+  `api/deploy/cron/cercol-db-backup`: the implementation this ADR
+  specifies.
+- ADR 0013 (Cloudflare front hosting, Proposed): rejected R2 coupling;
+  if 0013 is accepted later, Leg 2 can move to R2 with a one-line
+  remote change.
+- ADR 0006 (cron pattern for SEO ingest): the repo-ships-cron,
+  operator-installs-once pattern this decision reuses, minus its
+  silent-failure mode.
+- 2026-07-05 reliability audit: confirmed no pg_dump existed anywhere
+  on the server and that Hetzner machine-level backups are enabled.
diff --git a/docs/ops/runbook.md b/docs/ops/runbook.md
index 461fd4c2d..b306fd25e 100644
--- a/docs/ops/runbook.md
+++ b/docs/ops/runbook.md
@@ -350,8 +350,99 @@ read files under `/home/cercol/api`.
 cd /home/cercol/api && sudo -u postgres psql cercol < db/migrations/<NNN>-<name>.sql
 ```
 
-Backups are the operator's responsibility (`pg_dump`). Frequency
-and offsite copy procedure: TODO document.
+### Database backups (ADR 0017)
+
+Two legs, both driven by `api/deploy/backup/cercol-db-backup.sh`
+(root cron, daily 03:15 UTC, `/etc/cron.d/cercol-db-backup`):
+
+- **Leg 1 (on-box)**: `pg_dump -Fc` of the cercol database only, under
+  `/var/backups/cercol/`, 7 most recent dumps kept.
+- **Leg 2 (off-box)**: the same dump gpg-encrypted (AES256 symmetric,
+  passphrase in root-only `/root/.cercol-backup-passphrase`) and pushed
+  via rclone to the `gdrive:cercol-db-backups` Drive folder, 30-day
+  retention.
+
+Health check: `tail /home/cercol/logs/db-backup.log` and confirm
+`/home/cercol/logs/db-backup.FAILED` does NOT exist. The marker is
+written on any failure and removed on the next success.
+
+#### One-time install (as root on the server)
+
+```
+# 1. Passphrase file (fill in a strong passphrase; ALSO store it in the
+#    operator's password manager: without it the off-box copies are
+#    unrecoverable after box loss).
+[ -f /root/.cercol-backup-passphrase ] || \
+    printf '%s' 'REPLACE-WITH-STRONG-PASSPHRASE' > /root/.cercol-backup-passphrase
+chmod 0600 /root/.cercol-backup-passphrase
+
+# 2. rclone + Drive remote named exactly "gdrive" (interactive OAuth:
+#    pick "drive", scope "drive.file" is enough, follow the browser flow).
+command -v rclone > /dev/null || apt-get install -y rclone
+rclone listremotes | grep -q '^gdrive:$' || rclone config
+
+# 3. Log directory.
+install -d -o cercol -g cercol /home/cercol/logs
+
+# 4. Cron.
+install -m 0644 /home/cercol/api/api/deploy/cron/cercol-db-backup /etc/cron.d/
+
+# 5. First run by hand + restore test (next section).
+chmod +x /home/cercol/api/api/deploy/backup/cercol-db-backup.sh
+/home/cercol/api/api/deploy/backup/cercol-db-backup.sh
+tail -1 /home/cercol/logs/db-backup.log   # expect "BACKUP OK: ..."
+```
+
+#### Restore: from an on-box dump (logical errors, bad migration)
+
+```
+# as root
+latest=$(ls -1t /var/backups/cercol/cercol-*.dump | head -1)
+runuser -u postgres -- pg_restore --list "$latest" | head   # sanity: archive readable
+# Full restore into the live database (DESTRUCTIVE, think first;
+# prefer the scratch restore below to inspect data):
+runuser -u postgres -- pg_restore --clean --if-exists --no-owner \
+    --dbname=cercol "$latest"
+```
+
+For a single table, restore into a scratch database (next section) and
+copy the rows across with `psql` instead of touching the live database.
+
+#### Restore: from the off-box copy (box loss)
+
+```
+# on any machine with rclone configured for the same Drive account
+rclone ls gdrive:cercol-db-backups            # pick the newest .dump.gpg
+rclone copy gdrive:cercol-db-backups/cercol-<STAMP>.dump.gpg /tmp/
+gpg --batch --pinentry-mode loopback \
+    --passphrase-file /root/.cercol-backup-passphrase \
+    -o /tmp/cercol-restore.dump -d /tmp/cercol-<STAMP>.dump.gpg
+# then restore as in the on-box section, pointing at /tmp/cercol-restore.dump
+```
+
+The passphrase is NOT in the repo and NOT in Drive. If the box is lost
+the passphrase must come from the operator's password manager; storing
+it there is part of the install step above.
+
+#### Restore test (run once after install, then quarterly)
+
+```
+# as root; restores the newest dump into a scratch DB, checks a core
+# table, drops the scratch DB. Safe to run on the live server.
+latest=$(ls -1t /var/backups/cercol/cercol-*.dump | head -1)
+runuser -u postgres -- createdb cercol_restore_test
+runuser -u postgres -- pg_restore --no-owner --dbname=cercol_restore_test "$latest"
+runuser -u postgres -- psql -d cercol_restore_test -tc "SELECT COUNT(*) FROM results;"
+# expect a plausible row count (compare: same query against cercol)
+runuser -u postgres -- dropdb cercol_restore_test
+```
+
+#### Last resort: Hetzner machine-level backups
+
+Hetzner Cloud automatic backups are enabled on the VPS (whole-VM,
+crash-consistent, 7-day retention, restore from the Hetzner console).
+They roll back the ENTIRE machine including topquaranta, so they are
+the last resort for total box loss, never for cercol-only recovery.
 
 ### Blog slug redirects (Phase 17.10)