fix(alerting): reject null fireMode on ExchangeMatchCondition + repair in-flight rows

The rule editor wizard reset the condition payload on kind-change without
seeding a fireMode default; the ExchangeMatchCondition ctor allowed null to
pass through; AlertEvaluatorJob then NPE-looped every tick on a saved rule.

- core: compact ctor now rejects null fireMode (Jackson-deser path only — all
  production callers already pass a value).
- V14: repair existing EXCHANGE_MATCH rows with fireMode=null to
  PER_EXCHANGE + perExchangeLingerSeconds=300 (default matches the wizard).
- ui: ConditionStep.onKindChange seeds EXCHANGE_MATCH defaults so the
  Select's displayed fallback ("Per exchange") is actually in form state.
- ui: validateStep('condition', ...) now enforces fireMode presence + the
  mode-specific fields before the user reaches Review.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/pages/Alerts/RuleEditor/ConditionStep.tsx

@@ -14,10 +14,19 @@ export function ConditionStep({ form, setForm }: { form: FormState; setForm: (f:
     // Reset the condition payload so stale fields from a previous kind don't leak
     // into the save request. Preserve scope — it's managed on the scope step.
     const prev = form.condition as Record<string, unknown>;
+    const base: Record<string, unknown> = { kind, scope: prev.scope };
+    // EXCHANGE_MATCH must carry a fireMode — the backend ctor now rejects null.
+    // Seed PER_EXCHANGE + 300s linger so a user can save without touching every
+    // sub-field (matches what the form's Select displays by default).
+    if (kind === 'EXCHANGE_MATCH') {
+      base.fireMode = 'PER_EXCHANGE';
+      base.perExchangeLingerSeconds = 300;
+      base.filter = {};
+    }
     setForm({
       ...form,
       conditionKind: kind,
-      condition: { kind, scope: prev.scope } as FormState['condition'],
+      condition: base as FormState['condition'],
     });
   };
 

ui/src/pages/Alerts/RuleEditor/form-state.test.ts

@@ -47,4 +47,37 @@ describe('validateStep', () => {
     f.evaluationIntervalSeconds = 1;
     expect(validateStep('trigger', f).some((e) => /Evaluation interval/.test(e))).toBe(true);
   });
+
+  it('flags missing fireMode on EXCHANGE_MATCH condition step', () => {
+    const f = initialForm();
+    f.conditionKind = 'EXCHANGE_MATCH';
+    // Simulate the old bug: condition payload without a fireMode.
+    f.condition = { kind: 'EXCHANGE_MATCH', scope: {} } as typeof f.condition;
+    expect(validateStep('condition', f).some((e) => /Fire mode is required/.test(e))).toBe(true);
+  });
+
+  it('flags missing threshold/window on COUNT_IN_WINDOW', () => {
+    const f = initialForm();
+    f.conditionKind = 'EXCHANGE_MATCH';
+    f.condition = {
+      kind: 'EXCHANGE_MATCH',
+      scope: {},
+      fireMode: 'COUNT_IN_WINDOW',
+    } as unknown as typeof f.condition;
+    const errs = validateStep('condition', f);
+    expect(errs.some((e) => /Threshold is required/.test(e))).toBe(true);
+    expect(errs.some((e) => /Window/.test(e))).toBe(true);
+  });
+
+  it('passes when EXCHANGE_MATCH PER_EXCHANGE has linger seconds', () => {
+    const f = initialForm();
+    f.conditionKind = 'EXCHANGE_MATCH';
+    f.condition = {
+      kind: 'EXCHANGE_MATCH',
+      scope: {},
+      fireMode: 'PER_EXCHANGE',
+      perExchangeLingerSeconds: 300,
+    } as unknown as typeof f.condition;
+    expect(validateStep('condition', f)).toEqual([]);
+  });
 });

ui/src/pages/Alerts/RuleEditor/form-state.ts

@@ -147,6 +147,19 @@ export function validateStep(step: WizardStep, f: FormState): string[] {
   }
   if (step === 'condition') {
     if (!f.conditionKind) errs.push('Condition kind is required.');
+    if (f.conditionKind === 'EXCHANGE_MATCH') {
+      const c = f.condition as Record<string, unknown>;
+      if (!c.fireMode) {
+        errs.push('Fire mode is required.');
+      } else if (c.fireMode === 'PER_EXCHANGE') {
+        if (c.perExchangeLingerSeconds == null) {
+          errs.push('Linger seconds is required for PER_EXCHANGE.');
+        }
+      } else if (c.fireMode === 'COUNT_IN_WINDOW') {
+        if (c.threshold == null) errs.push('Threshold is required for COUNT_IN_WINDOW.');
+        if (c.windowSeconds == null) errs.push('Window (seconds) is required for COUNT_IN_WINDOW.');
+      }
+    }
   }
   if (step === 'trigger') {
     if (f.evaluationIntervalSeconds < 5) errs.push('Evaluation interval must be \u2265 5 s.');