CentralDbTestEnvironment sets five process-wide environment variables, and
Program's AddEnvironmentVariables() reads them at an unpredictable point during
host boot. With xUnit collection parallelization on, one fixture's teardown
could clear a var mid-boot for a sibling. Since the secrets adoption (G-4)
three of those keys are ${secret:...} references that fail closed, turning a
previously benign empty value into a SecretNotFoundException that aborts the
boot — an intermittent CI failure.
Adds a HostBootCollection that serializes every fixture booting a real host
while depending on that shared state, folding in the narrower "ActorSystem"
collection so its members stay serialized with each other as before. Site-role
fixtures stay parallel: they call Configuration.Sources.Clear(), dropping the
env-var provider, so they cannot participate in the race.
CentralDbTestEnvironment now also fails fast if two instances are ever live at
once, making a regression (a fixture added outside the collection) deterministic
rather than intermittent — this is what surfaced the disposed-CTS defect fixed
in the previous commit. Fixture teardown is try/finally so a throwing host
teardown can no longer strand the vars for the rest of the run.
Cost: Host.Tests runs ~2m30s -> ~4m10s; the serialized Central-boot classes are
most of the assembly's parallelism.
Fixes: Gitea #15
Joseph Doherty