Darling test flake: viewer-role grant test fails with 'tuple concurrently updated' #5560

A Darling live PostgreSQL test failed in CI with XX000: tuple concurrently updated. The test, QueryStatsHourLedgerTests.TheViewerRolesProvisionedGrants_ReadBothTables_AndWriteNeither, does not touch the code the PR changed.

Seen once, on 2026-10-08, in a pull request's Darling PG shard 1 (1 of 4336 failed). It has not been seen on dev yet.

The test creates a login role and runs the viewer-role statements on it (QueryStatsHourLedgerTests.cs:390-394). PostgreSQL raises this error when two sessions change the same catalog row at once, for example two GRANTs on one role, or role membership. Roles belong to the whole cluster, not one database. So another test class that runs at the same time on the same cluster can touch the same row.

To fix: find which statement raised it and which other test can run it at the same time. Then make the two not overlap (a shared collection, or a role name of each test's own). Keep every existing check. If the product's own provisioning can do the same thing when two services start together on one cluster, say so in the issue. Show the failure on purpose first, then show the fix holds.

Claude posting for Erik Darling.