The in-memory backend cannot run processor leases (ALB0024)

[VDBBjorn]

InMemoryBackendDescriptor refuses a module that turns leases on:

ALB0024 — The module enables processor leases (Leases.Enabled = true) but the
in-memory backend does not provide an IProcessorLeaseManager.
  → Switch to .WithPostgres(...) for a module that uses processor leases, or
    disable leases with .WithControlLoop(o => o with { Leases = o.Leases with { Enabled = false } }).

So the documented dev/test backend cannot exercise a control loop configured the way production is. Anyone developing against .WithInMemory() has to either turn leases off — and test a different topology from the one they ship — or run Postgres.

#158 builds a working in-memory IProcessorLeaseManager and IFencedCheckpointStore pair (TimeProvider-backed leases, monotonic fence tokens via Interlocked.Increment, both fencing guards) but deliberately keeps them in tests/Alberto.Tests, because promoting them is a feature and not a side effect of adding a conformance specification.

Fix

Promote both types into Alberto.InMemory, register them from InMemoryBuilderExtensions.RegisterBackend, and delete the ALB0024 validation failure. Leases.Enabled = true then works end to end on the in-memory backend, and the conformance specification from #158 runs against the adapter consumers actually get rather than a test double.

Why this is not free

Two things need deciding before it lands, which is why it is not folded into #158:

• Public API. Roughly 15 new entries in Alberto.InMemory/PublicAPI.Unshipped.txt, frozen under semver at 1.0. Worth reviewing the surface deliberately rather than inheriting whatever the test types happened to expose.
• CachingCheckpointStore behaviour change. It picks the fenced path with _inner as IFencedCheckpointStore (CachingCheckpointStore.cs:322). Making the in-memory checkpoint store implement the interface flips that cast from null to non-null for existing in-memory wiring. If the store is then handed a fencing context it cannot honour, the type test gives the wrong answer — the same shape as Only Alberto's own decorator can answer whether a checkpoint store can enumerate #155, where "implements the interface" and "can actually do it" came apart and needed a capability query to tell them apart.

Related

• The fencing seam has one adapter, no specification, and no coverage without Docker #158 — the conformance specification, which this makes meaningful against a shipped adapter
• Only Alberto's own decorator can answer whether a checkpoint store can enumerate #155 — the capability-query precedent the CachingCheckpointStore cast will likely need