Tell someone when the engine breaks

Everything that goes wrong already travelled the event bus, but the only
subscriber was the editor's websocket — so a flow quarantined at three in
the morning was invisible until someone opened the browser.

An alert manager now watches the same bus and forwards failures to ntfy,
email or a webhook. Most of what it does is decline to send: the same
node failing every second is one alert with a count of what followed, a
connection flapping up and down is muted until it settles, and nothing
gets past ten notifications an hour. Verified against a live instance —
six identical failures produced one alert carrying the real traceback
message.

Channels and rules are configured through the API, with a test send so a
channel can be proven before anything depends on it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011LF61rxW1FG5YCD2J9YqjY

frontend/src/client/schemas.gen.ts

@@ -1,5 +1,32 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
+export const AlertsConfigSchema = {
+    properties: {
+        enabled: {
+            type: 'boolean',
+            title: 'Enabled',
+            default: true
+        },
+        channels: {
+            items: {
+                '$ref': '#/components/schemas/Channel'
+            },
+            type: 'array',
+            title: 'Channels'
+        },
+        rules: {
+            items: {
+                '$ref': '#/components/schemas/Rule'
+            },
+            type: 'array',
+            title: 'Rules'
+        }
+    },
+    type: 'object',
+    title: 'AlertsConfig',
+    description: 'The whole alerting setup, as stored and as the API sees it.'
+} as const;
+
 export const Body_login_login_access_tokenSchema = {
     properties: {
         grant_type: {
@@ -135,6 +162,34 @@ export const Body_oauth_tokenSchema = {
     title: 'Body_oauth-token'
 } as const;
 
+export const ChannelSchema = {
+    properties: {
+        name: {
+            type: 'string',
+            title: 'Name'
+        },
+        kind: {
+            type: 'string',
+            enum: ['ntfy', 'smtp', 'webhook'],
+            title: 'Kind'
+        },
+        enabled: {
+            type: 'boolean',
+            title: 'Enabled',
+            default: true
+        },
+        config: {
+            additionalProperties: true,
+            type: 'object',
+            title: 'Config'
+        }
+    },
+    type: 'object',
+    required: ['name', 'kind'],
+    title: 'Channel',
+    description: 'Somewhere to send an alert.'
+} as const;
+
 export const DTypeSchema = {
     type: 'string',
     enum: ['float', 'int', 'str', 'bool', 'json'],
@@ -1013,6 +1068,33 @@ export const RenameRequestSchema = {
     title: 'RenameRequest'
 } as const;
 
+export const RuleSchema = {
+    properties: {
+        events: {
+            items: {
+                type: 'string'
+            },
+            type: 'array',
+            title: 'Events'
+        },
+        channels: {
+            items: {
+                type: 'string'
+            },
+            type: 'array',
+            title: 'Channels'
+        },
+        cooldown_s: {
+            type: 'number',
+            title: 'Cooldown S',
+            default: 900
+        }
+    },
+    type: 'object',
+    title: 'Rule',
+    description: 'Which events go to which channels.'
+} as const;
+
 export const RunRequestSchema = {
     properties: {
         inputs: {