The alert notebook says collection stopped for a fleet-level store alert #4756

A fleet-level store self-alert with no resolution row and no later firing reads "Unknown (not collected since ...)" in the alert notebook. That text says a collector stopped. But store self-alerts have no collector. The service process that evaluates them also serves this page, so the reason for that text, that the instrument is down, does not apply.

Only fleet-level store alerts reach this text through the collector check. An unresolved alert with no server returns earlier, and so does an alert with a blank metric name. No test passes a fleet-level store alert to this code. Two tests only mention the text.

Where (as of 64cd886)

• The text: Darling/PerformanceMonitor.Darling.Service/AlertNotebookEndpoint.cs:926-938. The fleet-level flag is set at :85-90.
• The earlier returns: :1069-1072 (no server) and :921-924 (blank metric).
• The tests that mention the text: Darling/Darling.Tests/AlertNotebookEndpointTests.cs:565 and :664.

Fix

For a fleet-level store alert with no resolution and no later firing, return "No resolution recorded".

Test that must fail first

A fleet-level store alert with no resolution row reads "No resolution recorded".