Split the single container-automation webhook URL into two independently
optional URLs — UpdateWebhookURL (fired on update/rollback/update-failed) and
HealWebhookURL (fired on auto-heal restart). The notifier routes each event to
its mechanism's URL by kind; an empty URL silences only that mechanism, so a
user can enable notifications for updates without heal (or vice-versa).
Settings gain both fields (each validated http/https, {{message}} allowed), the
NotificationPanel exposes two labeled inputs, and the golden migration output is
updated. Delivery path (goroutine/recover/timeout, {{message}} GET vs POST,
per-container stack message format) is unchanged.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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