refactor(alerts): drop AlertWebhook model

[TerrifiedBug]

Summary

Removes the legacy AlertWebhook model and its env-scoped fan-out, consolidating all alert delivery onto NotificationChannel(type=webhook) which already has the necessary infrastructure:

• channel drivers in src/server/services/channels/ (slack / email / pagerduty / webhook)
• DeliveryAttempt tracking via trackChannelDelivery
• per-rule routing via AlertRuleChannel
• backoff + retries via RetryService

AlertWebhook had none of these — just prisma.alertWebhook.findMany({ where: { environmentId } }) followed by raw fetch() calls. The webhook driver in channels/webhook.ts already does the same thing (URL validation, custom headers, optional HMAC signature) inside the channel framework.

Why

• Plaintext hmacSecret on AlertWebhook rows — no encryption-at-rest.
• No DeliveryAttempt tracking — failures had no audit trail.
• No retries on transient failures.
• No per-rule routing — every webhook fired for every alert in the env.

All of those are subsumed by NotificationChannel. The shape parity is exact (WebhookPayload and ChannelPayload were structurally identical), so the migration is purely a deletion.

Breaking change

Warning

Existing AlertWebhook rows are dropped by this PR's migration. Each one must be re-created as NotificationChannel(type=webhook) before merge — manually copy url / headers / hmacSecret into the channel config JSON, and link via AlertRuleChannel if rule-scoped routing is desired.

User has confirmed they will migrate prod rows by hand prior to deploy.

Files changed

Schema / migration

• prisma/schema.prisma — drops model AlertWebhook, the Environment.alertWebhooks relation, and DeliveryAttempt.webhookId.
• prisma/migrations/20260428000000_drop_alert_webhook/migration.sql — DROP TABLE IF EXISTS \"AlertWebhook\" CASCADE plus ALTER TABLE \"DeliveryAttempt\" DROP COLUMN IF EXISTS \"webhookId\".

Service callers

• src/server/services/webhook-delivery.ts — DELETED. formatWebhookMessage moved to channels/webhook.ts (only place it's used now).
• src/server/services/event-alerts.ts — drop deliverWebhooks(...); channel delivery now passes event.id for tracking.
• src/server/services/fleet-alert-service.ts — drop the AlertWebhook fan-out block; channel delivery is the single path.
• src/server/services/cost-alert.ts — drop the AlertWebhook query + loop.
• src/server/services/retry-service.ts — drop retryWebhook and the if (attempt.webhookId) branch in processRetries. WebhookPayload replaced with ChannelPayload.
• src/server/services/delivery-tracking.ts — drop trackWebhookDelivery and the webhookId parameter on trackDelivery.

tRPC

• src/server/routers/alert-webhooks.ts — DELETED.
• src/server/routers/alert.ts — drop alertWebhooksRouter registration.
• src/server/routers/alert-deliveries.ts — drop the if (attempt.webhookId) retry path; channel-only retry now.

Middleware / audit / actions

• src/trpc/init.ts — drop the AlertWebhook lookup in withTeamAccess.
• src/server/middleware/audit.ts — drop AlertWebhook from ENTITY_LOADERS, resolveTeamId, and resolveEnvironmentId.
• src/lib/audit-actions.ts — drop the alertWebhook.* action labels.

UI

• src/app/(dashboard)/alerts/_components/webhooks-section.tsx — DELETED.
• src/app/(dashboard)/alerts/page.tsx — remove the WebhooksSection import and render call. Two sections remain: NotificationChannelsSection and OutboundWebhooksSection.
• src/app/(dashboard)/alerts/_components/{delivery-status-panel,failed-deliveries-section}.tsx — drop the legacy_webhook channel-icon entry.

Tests

• DELETED: src/server/routers/__tests__/alert-webhooks.test.ts, src/server/services/__tests__/webhook-delivery.test.ts.
• ADDED: src/server/services/channels/__tests__/webhook.test.ts — covers formatWebhookMessage and the webhook driver (success / error status / HMAC / custom headers / SSRF / fetch failure / missing-url cases).
• UPDATED: fleet-alert-service.test.ts, cost-alert.test.ts, retry-service.test.ts, alert-deliveries.test.ts, alert-retry-delivery.test.ts, delivery-tracking.test.ts, heartbeat-async.test.ts — strip AlertWebhook mocks / assertions.

Follow-up (out of scope)

Encrypting NotificationChannel.config secrets at rest is tracked separately. Today the webhook driver reads hmacSecret directly from the JSON config, which is plaintext-at-rest just like AlertWebhook.hmacSecret was — so this PR doesn't regress security, but it doesn't fix it either. The fix is a follow-up Notion ticket already filed.

Test plan

• pnpm install clean
• npx prisma generate succeeds
• pnpm lint — no new warnings/errors
• npx tsc --noEmit — clean
• pnpm test — 2509 tests pass (5 pre-existing skips)
• pnpm build — production build succeeds
• After merge: alerts page renders 2 sections (NotificationChannels + OutboundWebhooks)
• After merge: creating a NotificationChannel(type=webhook) still works
• After merge: alerts that fire deliver via NotificationChannel only
• After merge: failed channel deliveries get retried via RetryService

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve retryability of existing webhook delivery attempts

Dropping DeliveryAttempt.webhookId here makes pre-migration failed webhook attempts unrecoverable: historical rows created via trackWebhookDelivery only have webhookId (with channelId = null), but the new retry paths now require channelId (retryDelivery throws on missing channel and RetryService skips). After this migration, those existing failures can still appear in failed-delivery lists but cannot actually be retried. Please migrate or clean up legacy DeliveryAttempt rows (or backfill a retry target) before removing the column.

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