The maintenance toggle lived in a package-level `bool` inside
`middleware/maintenance.go`. Flipping it via `PUT /admin/maintenance`
only updated the pod handling that request — the other N-1 pods stayed
open for traffic. In practice this meant deploys-in-progress or
incident playbooks silently failed to put the fleet into maintenance.
New storage:
* Migration `976_platform_settings.sql` adds a typed key/value table
(`value_bool` / `value_text` to avoid string parsing in the hot
path) and seeds `maintenance_mode=false`. Idempotent on re-run.
* `middleware/maintenance.go` rewritten around a `maintenanceState`
with a 10s TTL cache. `InitMaintenanceMode(db, logger)` primes the
cache at boot; `MaintenanceModeEnabled()` refreshes lazily when the
next request lands after the TTL. Startup `MAINTENANCE_MODE` env is
still honoured for fresh pods.
* `router.go` calls `InitMaintenanceMode` before applying the
`MaintenanceGin()` middleware so the first request sees DB truth.
* `PUT /api/v1/admin/maintenance` in `routes_core.go` now does an
`INSERT ... ON CONFLICT DO UPDATE` on the table *before* the
in-memory setter, so the flip survives restarts and propagates to
every pod within ~10s (one TTL window).
Tests: `TestMaintenanceGin_DBBacked` flips the DB row, waits past a
shrunk-for-test TTL, and asserts the cache picked up the change. All
four pre-existing tests preserved (`Disabled`, `Enabled_Returns503`,
`HealthExempt`, `AdminExempt`).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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