feat: add configurable notification dispatch retries (#1655)

* feat: add configurable notification dispatch retries

Allow each node to set 0-3 extra in-process delivery attempts with a fixed
one-second delay for routes, agents, and Test dispatch.

* fix: harden notification retry settings load/save and channel tests

Guard Delivery retries against failed and out-of-order same-node settings responses, and cover Slack/webhook retry classification alongside Discord.

* fix: clear Delivery retries saving state and correct screenshot alt

Separate save-request ownership from value-generation invalidation so a successful PATCH cannot leave Save retries stuck on Saving, reset saving on node switch, and align the Channels screenshot alt with the committed image.

* fix: surface invalid notification retry settings instead of false saved clamp

Align Channels GET handling with the backend strict 0-3 parser so stored values like 9 or 1.5 show as error needing repair, matching runtime fallback to 0 instead of displaying a clamped saved policy.

frontend/src/lib/notificationDispatchRetries.test.ts

@@ -0,0 +1,21 @@
+
+import { describe, it, expect } from 'vitest';
+import { parseNotificationDispatchRetries } from './notificationDispatchRetries';
+
+describe('parseNotificationDispatchRetries', () => {
+  it('accepts integers and digit strings 0-3', () => {
+    expect(parseNotificationDispatchRetries(0)).toBe(0);
+    expect(parseNotificationDispatchRetries(3)).toBe(3);
+    expect(parseNotificationDispatchRetries('2')).toBe(2);
+  });
+
+  it('rejects out-of-range, decimals, and non-canonical strings', () => {
+    expect(parseNotificationDispatchRetries(9)).toBeNull();
+    expect(parseNotificationDispatchRetries('9')).toBeNull();
+    expect(parseNotificationDispatchRetries(1.5)).toBeNull();
+    expect(parseNotificationDispatchRetries('1.5')).toBeNull();
+    expect(parseNotificationDispatchRetries(' 1')).toBeNull();
+    expect(parseNotificationDispatchRetries(null)).toBeNull();
+    expect(parseNotificationDispatchRetries(true)).toBeNull();
+  });
+});

frontend/src/lib/notificationDispatchRetries.ts

@@ -0,0 +1,16 @@
+/**
+ * Strict parser for notification_dispatch_retries (extra attempts, 0..3).
+ * Must stay aligned with backend/src/helpers/notificationDispatchRetries.ts:
+ * accepts JSON number integers or single-digit strings "0".."3" only.
+ */
+export function parseNotificationDispatchRetries(raw: unknown): number | null {
+  if (typeof raw === 'number') {
+    if (!Number.isInteger(raw) || raw < 0 || raw > 3) return null;
+    return raw;
+  }
+  if (typeof raw === 'string') {
+    if (!/^[0-3]$/.test(raw)) return null;
+    return Number(raw);
+  }
+  return null;
+}