From 4e30822fc02bb7253e7e7967685d94f7513a672e Mon Sep 17 00:00:00 2001
From: rcourtman <courtmanr@gmail.com>
Date: Tue, 24 Mar 2026 14:56:31 +0000
Subject: [PATCH] Drop monitored system reason alias fallback

---
 .../v6/internal/subsystems/api-contracts.md   |  5 +-
 .../__tests__/monitoredSystemLedger.test.ts   | 49 -------------------
 .../src/api/monitoredSystemLedger.ts          |  3 +-
 .../monitoredSystemModelGuardrails.test.ts    |  2 +-
 4 files changed, 4 insertions(+), 55 deletions(-)

diff --git a/docs/release-control/v6/internal/subsystems/api-contracts.md b/docs/release-control/v6/internal/subsystems/api-contracts.md
index 184d95e7f..e9a934bc2 100644
--- a/docs/release-control/v6/internal/subsystems/api-contracts.md
+++ b/docs/release-control/v6/internal/subsystems/api-contracts.md
@@ -260,9 +260,8 @@ The backend payload contract now emits only that structured object, and the
 frontend monitored-system client should parse that canonical wire contract
 directly rather than keeping flat alias fallback for
 `latest_included_signal_at`, `latest_included_signal_source`, or `last_seen`.
-The canonical nested status-reason timestamp is `reported_at`; older raw
-payloads may map a legacy nested `last_seen` input forward during rollout, but
-the normalized client contract must expose only `reported_at`.
+The canonical nested status-reason timestamp is `reported_at`, and the
+normalized client contract must expose only that field.
 That client contract must also fail closed when older or partial payloads omit
 the nested explanation object: the frontend may normalize missing explanation
 fields to empty reasons/surfaces plus a safe default summary, but it must not
diff --git a/frontend-modern/src/api/__tests__/monitoredSystemLedger.test.ts b/frontend-modern/src/api/__tests__/monitoredSystemLedger.test.ts
index b4bef5f1f..dae7a2e3f 100644
--- a/frontend-modern/src/api/__tests__/monitoredSystemLedger.test.ts
+++ b/frontend-modern/src/api/__tests__/monitoredSystemLedger.test.ts
@@ -242,55 +242,6 @@ describe('MonitoredSystemLedgerAPI', () => {
     ]);
   });
 
-  it('maps legacy status reason last_seen fields onto the canonical reported_at contract', async () => {
-    vi.mocked(apiFetchJSON).mockResolvedValueOnce({
-      systems: [
-        {
-          name: 'Tower',
-          type: 'host',
-          status: 'warning',
-          status_explanation: {
-            summary: 'At least one included source is stale, so Pulse marks this monitored system as warning.',
-            reasons: [
-              {
-                kind: 'source-stale',
-                name: 'Tower',
-                type: 'host',
-                source: 'agent',
-                status: 'stale',
-                last_seen: '2026-03-23T11:55:00Z',
-                summary: 'Agent data for Tower is stale (last reported 2026-03-23T11:55:00Z).',
-              },
-            ],
-          },
-          latest_included_signal: {
-            name: 'tower.local',
-            type: 'docker-host',
-            source: 'docker',
-            at: '2026-03-23T11:59:50Z',
-          },
-          source: 'multiple',
-        },
-      ],
-      total: 1,
-      limit: 5,
-    });
-
-    const result = await MonitoredSystemLedgerAPI.getLedger();
-
-    expect(result.systems[0]?.status_explanation?.reasons).toEqual([
-      {
-        kind: 'source-stale',
-        name: 'Tower',
-        type: 'host',
-        source: 'agent',
-        status: 'stale',
-        reported_at: '2026-03-23T11:55:00Z',
-        summary: 'Agent data for Tower is stale (last reported 2026-03-23T11:55:00Z).',
-      },
-    ]);
-  });
-
   it('fails closed to unknown for unsupported status values', async () => {
     vi.mocked(apiFetchJSON).mockResolvedValueOnce({
       systems: [
diff --git a/frontend-modern/src/api/monitoredSystemLedger.ts b/frontend-modern/src/api/monitoredSystemLedger.ts
index 50e51d39c..91f45da3f 100644
--- a/frontend-modern/src/api/monitoredSystemLedger.ts
+++ b/frontend-modern/src/api/monitoredSystemLedger.ts
@@ -89,7 +89,6 @@ interface MonitoredSystemLedgerRawStatusExplanation
 interface MonitoredSystemLedgerRawStatusReason
   extends Omit<MonitoredSystemLedgerStatusReason, 'reported_at'> {
   reported_at?: string;
-  last_seen?: string;
 }
 
 export class MonitoredSystemLedgerAPI {
@@ -154,7 +153,7 @@ function normalizeMonitoredSystemLedgerStatusReason(
     type: reason.type,
     source: reason.source,
     status: normalizeMonitoredSystemLedgerStatusReasonStatus(reason.status),
-    reported_at: reason.reported_at ?? reason.last_seen ?? '',
+    reported_at: reason.reported_at ?? '',
     summary: reason.summary,
   };
 }
diff --git a/frontend-modern/src/components/Settings/__tests__/monitoredSystemModelGuardrails.test.ts b/frontend-modern/src/components/Settings/__tests__/monitoredSystemModelGuardrails.test.ts
index 01b3cffe1..6d647b6a3 100644
--- a/frontend-modern/src/components/Settings/__tests__/monitoredSystemModelGuardrails.test.ts
+++ b/frontend-modern/src/components/Settings/__tests__/monitoredSystemModelGuardrails.test.ts
@@ -256,7 +256,7 @@ describe('monitored-system model guardrails', () => {
     expect(monitoredSystemLedgerApiSource).not.toContain('last_seen: string;');
     expect(monitoredSystemLedgerApiSource).not.toContain('latest_included_signal_at?: string;');
     expect(monitoredSystemLedgerApiSource).not.toContain('latest_included_signal_source?: string;');
-    expect(monitoredSystemLedgerApiSource).toContain('last_seen?: string;');
+    expect(monitoredSystemLedgerApiSource).not.toContain('last_seen?: string;');
     expect(monitoredSystemLedgerApiSource).not.toContain(
       'All included top-level collection paths currently report online status.',
     );