Deduplicate ExecutionId/InstanceId envelope across DotnetTest IPC serializers

[Evangelink]

Fixes #9812.

Summary

Four dotnet test IPC serializers — DiscoveredTestMessagesSerializer, TestResultMessagesSerializer, TestInProgressMessagesSerializer, and FileArtifactMessagesSerializer — shared an identical top-level ExecutionId/InstanceId envelope in their DeserializeCore/SerializeCore methods (the same ExecutionId/InstanceId switch cases + field-count/write scaffolding, ~18 lines per serializer). This PR extracts that shared scaffold.

Changes

• Added two stateless static helpers to the shared BaseSerializer (IPC/Serializers/BaseSerializer.cs):
  • ReadExecutionScopedFields(...) — reads the leading ExecutionId (id 1) / InstanceId (id 2) string fields and delegates every other field id to a caller-supplied payload reader, returning the two envelope values.
  • WriteExecutionScopedFields(...) — writes the field-count prefix, the ExecutionId/InstanceId fields, then invokes a payload writer.
• Refactored the four serializers to use the helpers and dropped their now-redundant top-level GetFieldCount(<Messages>) methods (the per-message-item GetFieldCount overloads are unchanged).
• Updated the tracked InternalAPI.Unshipped.txt for the platform and the extension projects that embed these shared-source serializers.

The helpers are stateless (the serializers are registered as singletons), so no shared mutable state is introduced.

Wire compatibility

The field ids (ExecutionId=1, InstanceId=2, message lists), their order and layout are unchanged — this is a pure code-dedup refactor. These files are also vendored into dotnet/sdk, so the round-trip contract is preserved.

Verification

• Microsoft.Testing.Platform.DotnetTestProtocolContract.UnitTests (standalone shared-source round-trip contract): 21/21 passed.
• Microsoft.Testing.Platform.UnitTests ProtocolTests + ProtocolEdgeCaseTests: 33/33 passed.
• Full solution/analyzer build succeeds (0 warnings, 0 errors).

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Pull request overview

Deduplicates execution-scoped envelope handling across four dotnet test IPC serializers while preserving wire compatibility.

Changes:

• Adds shared read/write envelope helpers.
• Refactors four serializers to use them.
• Updates tracked internal API declarations.

Show a summary per file

File	Description
BaseSerializer.cs	Adds shared envelope helpers.
DiscoveredTestMessagesSerializer.cs	Uses shared envelope handling.
TestResultMessagesSerializer.cs	Uses shared envelope handling.
TestInProgressMessagesSerializer.cs	Uses shared envelope handling.
FileArtifactMessagesSerializer.cs	Uses shared envelope handling.
Microsoft.Testing.Platform/InternalAPI/net/InternalAPI.Unshipped.txt	Tracks new helper APIs.
Microsoft.Testing.Platform/InternalAPI/InternalAPI.Unshipped.txt	Tracks new helper APIs.
Microsoft.Testing.Extensions.TrxReport/InternalAPI/InternalAPI.Unshipped.txt	Tracks shared-source APIs.
Microsoft.Testing.Extensions.Retry/InternalAPI/InternalAPI.Unshipped.txt	Tracks shared-source APIs.
Microsoft.Testing.Extensions.MSBuild/InternalAPI.Unshipped.txt	Tracks shared-source APIs.
Microsoft.Testing.Extensions.HangDump/InternalAPI/InternalAPI.Unshipped.txt	Tracks shared-source APIs.

Review details

• Files reviewed: 11/11 changed files
• Comments generated: 1
• Review effort level: Medium

[github-actions]

Note

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Review Summary

Clean dedup refactor — the wire format is preserved, the helpers are stateless, and the field-id constants match all four serializers. No issues found.

#	Dimension	Verdict
1	Correctness	✅ Pass — field ids 1/2 match all four *FieldsId classes; read/write logic is equivalent to the inlined original.
2	Bug risk	✅ Pass — no behavioral change.
3	Edge cases	✅ Pass — null ExecutionId/InstanceId handled identically (conditional field count + WriteField no-ops on null).
4	Security	✅ N/A — no auth, no user input parsing changes.
5	Performance	✅ Pass — one extra delegate allocation per call, but serializers are not hot-path; acceptable.
6	Concurrency	✅ Pass — helpers are stateless static; no shared mutable state.
7	Error handling	✅ Pass — unchanged from original.
8	API design	✅ Pass — protected static scope is appropriate; tuple return is idiomatic.
9	Naming	✅ Pass — ReadExecutionScopedFields/WriteExecutionScopedFields clearly describe purpose.
10	Documentation	✅ Pass — XML docs on both helpers; inline comment explains wire-id contract.
11	Style / formatting	✅ Pass — consistent with codebase conventions.
12	DRY / duplication	✅ Pass — this is the point of the PR; duplication eliminated.
13	Testability	✅ Pass — existing serializer round-trip tests cover the refactored paths.
14	Backward compat	✅ Pass — wire ids and layout unchanged; vendored-into-SDK contract preserved.
15	Public API surface	✅ Pass — InternalAPI.Unshipped.txt updated in all 6 locations.
16	Localization	✅ N/A
17	Logging / diagnostics	✅ N/A
18	Disposal / resources	✅ N/A
19	Configuration	✅ N/A
20	Dependencies	✅ Pass — no new dependencies.
21	TODOs	✅ Pass — none introduced.
22	Test coverage	✅ Pass — covered by existing IPC serializer unit tests.

Overall: No issues. Straightforward and safe dedup refactor.

Minor observation (non-blocking): DisplayMessageSerializer and AzureDevOpsLogMessageSerializer share the same ExecutionId=1/InstanceId=2 envelope pattern but weren't included in this refactor. Could be a follow-up if desired.

[Copilot]

Review details

• Files reviewed: 11/11 changed files
• Comments generated: 2
• Review effort level: Medium

[Copilot]

Review details

• Files reviewed: 11/11 changed files
• Comments generated: 0 new
• Review effort level: Medium