feat(notifications): add a failed-check threshold for node.down alerts (#6768)

One lost heartbeat on a lossy link flipped a node offline and sent node.down,
and the next probe sent node.up, so a flaky node flooded Telegram, email and
Discord with alert pairs.

A new nodeDownThreshold setting (default 1, today's behaviour) works like
outboundDownThreshold: node.down fires once the failed-check streak reaches it,
once per outage, and node.up only after a node.down was sent. The announcement
is persisted in nodes.down_notified, so a restart inside the threshold window
neither drops the outage's node.down nor re-announces nodes already reported
offline; nodes offline at upgrade are seeded as announced.

frontend/src/generated/examples.ts

@@ -39,6 +39,7 @@ export const EXAMPLES: Record<string, unknown> = {
     "ldapUserAttr": "",
     "ldapUserFilter": "",
     "ldapVlessField": "",
+    "nodeDownThreshold": 1,
     "outboundDownThreshold": 1,
     "pageSize": 0,
     "panelOutbound": "",
@@ -227,6 +228,7 @@ export const EXAMPLES: Record<string, unknown> = {
     "ldapUserAttr": "",
     "ldapUserFilter": "",
     "ldapVlessField": "",
+    "nodeDownThreshold": 1,
     "outboundDownThreshold": 1,
     "pageSize": 0,
     "panelOutbound": "",

frontend/src/generated/schemas.ts

@@ -126,6 +126,11 @@ export const SCHEMAS: Record<string, unknown> = {
       "ldapVlessField": {
         "type": "string"
       },
+      "nodeDownThreshold": {
+        "maximum": 100,
+        "minimum": 1,
+        "type": "integer"
+      },
       "outboundDownThreshold": {
         "maximum": 100,
         "minimum": 1,
@@ -613,6 +618,7 @@ export const SCHEMAS: Record<string, unknown> = {
       "ldapUserAttr",
       "ldapUserFilter",
       "ldapVlessField",
+      "nodeDownThreshold",
       "outboundDownThreshold",
       "pageSize",
       "panelOutbound",
@@ -906,6 +912,11 @@ export const SCHEMAS: Record<string, unknown> = {
       "ldapVlessField": {
         "type": "string"
       },
+      "nodeDownThreshold": {
+        "maximum": 100,
+        "minimum": 1,
+        "type": "integer"
+      },
       "outboundDownThreshold": {
         "maximum": 100,
         "minimum": 1,
@@ -1401,6 +1412,7 @@ export const SCHEMAS: Record<string, unknown> = {
       "ldapUserAttr",
       "ldapUserFilter",
       "ldapVlessField",
+      "nodeDownThreshold",
       "outboundDownThreshold",
       "pageSize",
       "panelOutbound",

frontend/src/generated/types.ts

@@ -47,6 +47,7 @@ export interface AllSetting {
   ldapUserAttr: string;
   ldapUserFilter: string;
   ldapVlessField: string;
+  nodeDownThreshold: number;
   outboundDownThreshold: number;
   pageSize: number;
   panelOutbound: string;
@@ -236,6 +237,7 @@ export interface AllSettingView {
   ldapUserAttr: string;
   ldapUserFilter: string;
   ldapVlessField: string;
+  nodeDownThreshold: number;
   outboundDownThreshold: number;
   pageSize: number;
   panelOutbound: string;

frontend/src/generated/zod.ts

@@ -63,6 +63,7 @@ export const AllSettingSchema = z.object({
   ldapUserAttr: z.string(),
   ldapUserFilter: z.string(),
   ldapVlessField: z.string(),
+  nodeDownThreshold: z.number().int().min(1).max(100),
   outboundDownThreshold: z.number().int().min(1).max(100),
   pageSize: z.number().int().min(0).max(1000),
   panelOutbound: z.string(),
@@ -253,6 +254,7 @@ export const AllSettingViewSchema = z.object({
   ldapUserAttr: z.string(),
   ldapUserFilter: z.string(),
   ldapVlessField: z.string(),
+  nodeDownThreshold: z.number().int().min(1).max(100),
   outboundDownThreshold: z.number().int().min(1).max(100),
   pageSize: z.number().int().min(0).max(1000),
   panelOutbound: z.string(),