=== SCENARIO C — a backup-family event carrying stack_name must NOT split per app ===
subject: crossdrive_failed — severity error, reaches the operator leg, carries stack_name
through CrossDriveDetails. Two DIFFERENT apps: if the key had split, both would send.

HOW THE 'BEFORE' VALUE WAS OBTAINED, two independent ways:
  (a) derivation from v0.107.0's expression, which is customerID:eventType + tier + run and
      carries no app term, so for this payload it is exactly 'demo-hp:crossdrive_failed';
  (b) TestR389_NoOtherEventTypeKeyChanges models that v0.107.0 expression INLINE and compares
      it against the live one for 12 event types — with a positive control proving the test
      can see a key change before it reports that none occurred.
The live key printed below must equal that.

  T_C=2026-08-23T12:03:44Z
  crossdrive_failed opengist http=200
  crossdrive_failed calibre-web http=200
