fix(grpc): preserve expected-version failures with unknown revisions

[yordis]

• Unknown stream revisions must not crash append calls or be reported as absent streams during the transport migration.
• Large revisions, catch-up subscriptions, hash collisions, and restart continuity need direct gRPC regression signals before legacy coverage is retired.

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PR Summary

Medium Risk
Changes client-visible gRPC error semantics for expected-version failures on append paths; incorrect mapping could break optimistic concurrency handling for edge cases.

Overview
Fixes gRPC WrongExpectedVersion handling so append and batch append no longer treat every non–-1 CurrentVersion as a concrete revision or mislabel no stream when the server only knows the stream state is unknown (e.g. hash-collision read limits).

Introduces CurrentStreamVersion to classify WriteEventsCompleted.CurrentVersion as unknown, no stream (ExpectedVersion.NoStream), or a known StreamRevision, and wires that through Status.WrongExpectedVersion, WrongExpectedVersion.Create, Streams.Append, and Streams.BatchAppend. When the version is unknown, responses omit current revision / no-stream fields instead of forcing one.

Adds long-running gRPC regression tests (shared GrpcStreamEdgeOperations helper) for restart continuity, hash-collision boundaries, and revisions above int.MaxValue (read, append, wrong-version errors, catch-up subscriptions).

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📥 Commits

Reviewing files that changed from the base of the PR and between 30c4568 and 851727c.

📒 Files selected for processing (7)

• src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/GrpcStreamEdgeOperations.cs
• src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/StreamRevisionAboveIntMaxTests.cs
• src/EventStore.Core/Services/Transport/Grpc/CurrentStreamVersion.cs
• src/EventStore.Core/Services/Transport/Grpc/Status.cs
• src/EventStore.Core/Services/Transport/Grpc/Streams.Append.cs
• src/EventStore.Core/Services/Transport/Grpc/Streams.BatchAppend.cs
• src/EventStore.Core/Services/Transport/Grpc/WrongExpectedVersion.cs

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Walkthrough

gRPC append responses now use CurrentStreamVersion to distinguish unknown, no-stream, and known revisions. New tests cover appends across restarts, hash-collision boundaries, and stream operations above int.MaxValue.

Changes

gRPC Stream Revision Handling

Layer / File(s)	Summary
Typed current-version response handling src/EventStore.Core/Services/Transport/Grpc/CurrentStreamVersion.cs, src/EventStore.Core/Services/Transport/Grpc/WrongExpectedVersion.cs, src/EventStore.Core/Services/Transport/Grpc/Status.cs, src/EventStore.Core/Services/Transport/Grpc/Streams.Append.cs, src/EventStore.Core/Services/Transport/Grpc/Streams.BatchAppend.cs	CurrentStreamVersion represents unknown, no-stream, or known stream revisions. Append and wrong-expected-version responses set current-version fields for no-stream and known revisions; unknown values leave those fields unset.
Restart and collision test coverage src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/GrpcStreamEdgeOperations.cs, src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/AppendAcrossRestartGrpcTests.cs, src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/HashCollisionGrpcBoundaryTests.cs	The test helper supports appends with expected revisions and stream reads. Tests cover appends after restart, metadata stream revisions, and reads and appends for colliding streams.
Revisions above int.MaxValue src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/StreamRevisionAboveIntMaxTests.cs	Tests cover forward and backward reads, expected-revision appends, wrong-expected-version responses, and catch-up subscriptions above int.MaxValue.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 85172

The unknown-version regression is already covered by the collision tests. No identified issue prevents merging after normal checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 85172

The append permission check remains in place, and the response mapping appears to preserve existing behavior. External code that calls the formerly public helper methods may, however, need to change.

Retained concerns

• Low · architecture · inferred: Two formerly public response-building methods become internal and change signature. External assemblies using either method could lose source compatibility; whether these helpers are supported external APIs or have external callers is unknown.

Security review details

Security Blast Radius

• inferred — For the inspected single-append path, a caller-controlled stream identifier remains subject to a write-access check before an append is submitted. No broader caller authority is evident from the response-mapping change.

Trust Boundaries and Controls

• observed — The single-append handler derives the user from the request context and checks write access against the requested stream before publishing events with that user and the requested expected version.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 9 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the primary change: preserving gRPC expected-version failures when stream revisions are unknown.
Description check	✅ Passed	The description directly matches the changeset and objectives. It identifies unknown revisions and the added gRPC regression coverage for large revisions, subscriptions, hash collisions, and restart c…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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_{A rabbit checks each stream at night
Through restart, revisions land just right
Above int’s peak, the events run
Colliding hashes hide from none
Fresh appends greet the morning sun}

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Actionable comments posted: 1

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Inline comments:
In
`@src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/StreamRevisionAboveIntMaxTests.cs`:
- Around line 1-105: In appends_at_a_revision_above_int_max, extend the mismatch
assertion to unpack the WrongExpectedVersion detail and verify that its
current-stream-revision option is present and equals FirstRevision + 5.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

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Run ID: cd961d75-92e7-40a7-b4ef-9bf14cef99a9

📥 Commits

Reviewing files that changed from the base of the PR and between 56eb784 and 065a7a0.

📒 Files selected for processing (8)

• src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/AppendAcrossRestartGrpcTests.cs
• src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/GrpcStreamEdgeOperations.cs
• src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/HashCollisionGrpcBoundaryTests.cs
• src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/StreamRevisionAboveIntMaxTests.cs
• src/EventStore.Core/Services/Transport/Grpc/Status.cs
• src/EventStore.Core/Services/Transport/Grpc/Streams.Append.cs
• src/EventStore.Core/Services/Transport/Grpc/Streams.BatchAppend.cs
• src/EventStore.Core/Services/Transport/Grpc/WrongExpectedVersion.cs

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