feat(ops): daily DB backup schedule, idempotent install via session-start hook

[metazen11]

Daily pg_dump schedule. Pre-existing scripts/backup.sh (with rotation logic) was already in the repo; this PR wires it into a macOS launchd job that fires at 03:14 daily, AND adds idempotent auto-install via the session-start hook.

Not tied to a particular issue — surfaced while taking a manual safety backup before #28 work and noticing that the backup script existed but had never been scheduled.

Summary

• scripts/install_backup_schedule.sh — installer with --check + --uninstall. Renders the launchd plist with absolute paths; bootstraps the job.
• scripts/com.metazen.agent-memory-backup.plist — launchd template (StartCalendarInterval = 03:14 daily; Hour: 3 / Minute: 14 — off the :00 mark per scheduling guidance).
• hooks/ensure-services.js — new ensureBackupSchedule() runs at end of Main. Idempotent: re-installs only when the template is newer than the installed plist OR the target is missing. macOS-only. Failures debug-logged and swallowed — never blocks session start.
• scripts/backup.sh — bug fixes (see below).
• docs/backups.md — operator reference.

scripts/backup.sh bug fixes

The pre-existing script hard-coded user=agentmem and didn't carry a password, which silently failed against the real dev setup (which uses DATABASE_URL from .env).

Auth resolution order is now:

1. DATABASE_URL (preferred — matches the running FastAPI server's DSN).
2. POSTGRES_USER + PGPASSWORD env var fallback.
3. Defaults: agentmem / agent_memory / 5432.

Plus a min-size guard: if the produced file is < 1 KB the script deletes it and exits 1. Catches silent auth-failure cases that would otherwise leave a useless 20-byte .gz in data/backups/.

Test plan

• bash scripts/install_backup_schedule.sh installs the plist and bootstraps the job.
• bash scripts/install_backup_schedule.sh --check reports plist installed + job loaded.
• launchctl list | grep com.metazen.agent-memory-backup shows the loaded job.
• bash scripts/backup.sh produces a valid 319 MB gzipped dump.
• Rotation keeps only the 3 most recent daily_*.sql.gz files; manual snapshots with other prefixes are preserved.
• Min-size guard removes a 20-byte failed-auth file from earlier testing.
• hooks/ensure-services.js runs through node -c parse (already in production every session).
• Cannot test in CI: the launchd 03:14 daily fire happens out-of-process. Will be verified by checking data/backups/ after tomorrow's run.

Verification commands

bash scripts/install_backup_schedule.sh --check
ls -lht data/backups/
launchctl list | grep com.metazen.agent-memory-backup
tail -f ~/Library/Logs/agent-memory-backup.log

Rollback

bash scripts/install_backup_schedule.sh --uninstall

Reverting the commit also reverts the ensure-services.js hook, so subsequent sessions won't re-install the job. Existing dumps in data/backups/ stay; data is never destroyed.

Out of scope

• Linux cron path is sketched in the installer (crontab -e fallback) but not exercised on a real Linux host — needs verification when the second-Mac / Linux deploy lands (issue ops: move agentMemory off Dropbox to local SSD #14).
• Off-machine backup destination (S3/B2) — out of scope. Local-only.
• Encryption of dumps at rest — out of scope. Dumps may contain redacted-but-not-encrypted data.

Why not in #28 instead

This is operational infra, independent of the v2 fine-tune pipeline. Wanted a safety backup before #28's bulk import (which it now has — see data/backups/pre_v2_backfill_20260513_211653.sql.gz), and discovered the schedule was missing. Decoupling so the backup fix can ship independently.