#4617 PR 8: section 3a remainder + section 5 #4611 single-DB regression pin

[jeremydmiller]

Eighth #4617 slice — 7 new tests across three files, covering section 3a remaining items + the single-DB conjoined variant of the #4611 regression already pinned for sharded.

3a — Return-shape coverage (3 tests)

AppendWrite/append_return_shapes_under_partitioning.cs

The Append + StartStream overload matrix has multiple shapes (params object[], IEnumerable<object>, single-event-via-params-of-one). Each must route through the bulk mt_quick_append_events function and land in the owning tenant's partition. Pinned per the spec's "Return shapes" item so a future overload-resolution change or appender refactor can't silently reshape what hits the partitioned tables.

• append_via_params_object_array_lands_in_tenants_partition
• append_via_IEnumerable_lands_in_tenants_partition
• append_single_event_via_params_array_of_one_lands_in_tenants_partition (boundary case)

3a — Event-metadata propagation (2 tests)

AppendWrite/event_metadata_propagation_under_partitioning.cs

Per the spec's TenantPropagation pin (#4424) and metadata-flow pin:

• event_TenantId_equals_stream_TenantId_under_partitioning — shared fixture; pins the TenantPropagation invariant that every event's TenantId equals the stream's tenant, never null.
• event_optional_metadata_propagation_under_partitioning — own DocumentStore because CorrelationId / CausationId / Headers / UserName columns are opt-in (MetadataConfig.* = true). Pins that all four propagate from session → each event in the bulk batch, AND that TenantId stays paired with the right tenant alongside the opt-in metadata.

Section 5 — #4611 single-DB regression pin (2 tests)

Regressions/Bug_4611_mandatory_stream_type_under_partitioning.cs

The sharded variant already lives in Sharded/sharded_tenancy_per_tenant_events.cs from PR #3. This is the single-DB conjoined variant the spec specifically calls out as missing. Own-store because UseMandatoryStreamTypeDeclaration is a store-wide flag.

• StartStream_with_aggregate_type_followed_by_Append_works — Start + Append both succeed; mt_streams row exists with type = aggregate alias (the headline StartStream doesn't create mt_streams row under per-tenant event partitioning (sharded) → NonExistentStream on later append (9.5.0) #4611 surface).
• untyped_StartStream_still_throws_StreamTypeMissingException — companion pin: the API-level guard in EventStore.StartStream STILL fires synchronously for the no-type overload. PR Fix #4611: allow StartStream with mandatory stream types under per-tenant event partitioning #4613's fix didn't (and shouldn't) weaken this guard.

Verified

Suite	Before	After
TenantPartitionedEventsTests net9.0	111/111	118/118
TenantPartitionedEventsTests net10.0	111/111	118/118

Subsequent PRs per the #4617 checklist

• 3c remaining: EventProjection, FlatTableProjection, MultiStream RollUpByTenant + AcrossTenants, custom IAggregateGrouper, raw IProjection, lifecycle equivalence
• 3d remaining: AddMartenManagedTenantsAsync(Guid[]) N-format pin, sharded one-DB-per-shard, IDynamicTenantSource lifecycle
• 3e remaining: DeleteAllTenantDataAsync orphan-sequence leak pin, RemoveMartenManagedTenantsAsync, AssertDatabaseMatchesConfigurationAsync drift, DDL generation, PerTenantEventSequences schema-object correctness, AutoCreate matrix
• 3f DCB partitioned coverage
• Section 4 daemon in-depth
• Section 5 remaining: 42P01 / 42P16 / 42P07 / MT002-rebuild regression families
• 3a remaining: Quick vs QuickWithServerTimestamps timestamp-source, seq_id gap-after-failed-batch
• 3b deferred items

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