From 1b0f236cc654499c3d731ae0fa2d94206c8d2ec1 Mon Sep 17 00:00:00 2001
From: Kyle Bernhardy <kyle@harperdb.io>
Date: Sat, 11 Jul 2026 12:10:28 -0600
Subject: [PATCH] fix(status): require total, not errors, for the error-rate
 panel
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The error-rate derived-metric override declared ['count', 'errors'], but
recomputeErrorRate reads count and total — never errors. On a Harper
whose success records lack an errors column, MetricPanel showed a false
"field unavailable" empty state for a chart that would render fine,
while a genuinely missing total (which silently zeroes the numerator and
renders a flat 100% error rate) was never flagged.

Change the override to ['count', 'total'] and pin it behaviorally: the
new tests feed recomputeErrorRate records with each declared required
field omitted and assert the output changes (load-bearing), and assert
that omitting errors leaves the output untouched — so the test fails if
either the override or the recompute drifts.

Fixes #1441

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UZEaYdKFXuQw2Hf6XpPdEV
---
 .../analytics/lib/specRequiredFields.test.ts  | 33 +++++++++++++++++++
 .../analytics/lib/specRequiredFields.ts       |  2 +-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/features/instance/status/analytics/lib/specRequiredFields.test.ts b/src/features/instance/status/analytics/lib/specRequiredFields.test.ts
index a50464cdb..4b78ea5a4 100644
--- a/src/features/instance/status/analytics/lib/specRequiredFields.test.ts
+++ b/src/features/instance/status/analytics/lib/specRequiredFields.test.ts
@@ -1,4 +1,6 @@
 import { describe, expect, it } from 'vitest';
+import { recomputeErrorRate } from '../pipeline/derived/error-rate.tsx';
+import type { AnalyticsDataPoint, TimeRange } from '../types/analytics.ts';
 import { getSpecRequiredFields } from './specRequiredFields.ts';
 
 describe('getSpecRequiredFields', () => {
@@ -29,6 +31,37 @@ describe('getSpecRequiredFields', () => {
 
 		const errRate = getSpecRequiredFields('error-rate');
 		expect(errRate).toContain('count');
+		expect(errRate).toContain('total');
+	});
+
+	// Pin the error-rate override to what `recomputeErrorRate` actually reads.
+	// The override once listed `errors` (which the recompute never touches),
+	// blanking a working chart on Harpers whose success records lack that
+	// column — while a genuinely missing `total` went unflagged (#1441).
+	describe('error-rate override vs recomputeErrorRate behavior', () => {
+		const window: TimeRange = { startTime: 0, endTime: 60_000 };
+		// Σ-arithmetic fixture from the error-rate spec: baseline ≈ 0.0188.
+		const records: AnalyticsDataPoint[] = [
+			{ time: 1_000, node: 'n1', path: '/api', count: 1000, total: 990, errors: 10 },
+			{ time: 1_000, node: 'n1', path: '/api', count: 10, total: 1, errors: 9 },
+		];
+		const firstY = (recs: AnalyticsDataPoint[]) =>
+			recomputeErrorRate(recs, window, ['n1']).series[0]?.points[0]?.y ?? null;
+		const omit = (field: string) => records.map(({ [field]: _omitted, ...rest }) => rest as AnalyticsDataPoint);
+
+		it('every declared required field is load-bearing for the recompute', () => {
+			const baseline = firstY(records);
+			expect(baseline).toBeCloseTo(1 - 991 / 1010, 6);
+			for (const field of getSpecRequiredFields('error-rate')) {
+				expect(firstY(omit(field)), `dropping required field "${field}" should change the output`)
+					.not.toEqual(baseline);
+			}
+		});
+
+		it('does NOT require `errors` — the recompute never reads it', () => {
+			expect(getSpecRequiredFields('error-rate')).not.toContain('errors');
+			expect(firstY(omit('errors'))).toEqual(firstY(records));
+		});
 	});
 
 	it('returns [] for a derived metric without an explicit override', () => {
diff --git a/src/features/instance/status/analytics/lib/specRequiredFields.ts b/src/features/instance/status/analytics/lib/specRequiredFields.ts
index d727aa7c4..ea47c1be1 100644
--- a/src/features/instance/status/analytics/lib/specRequiredFields.ts
+++ b/src/features/instance/status/analytics/lib/specRequiredFields.ts
@@ -9,7 +9,7 @@ import type { FieldExpr, FieldSpec, MetricSpec, Transform } from '../types/analy
  *  the source-record fields the recompute reads. */
 const DERIVED_REQUIRED_FIELDS: Record<string, readonly string[]> = {
 	'request-rate': ['count', 'period'],
-	'error-rate': ['count', 'errors'],
+	'error-rate': ['count', 'total'],
 	// mqtt-traffic-* delegate to runPipeline against bytes-{sent,received}
 	// inner specs, so they are covered transitively through the source spec
 	// and the renderer fetches the source metric directly.