Forward MSBuild build/tasks/details telemetry event

[jankratochvilcz]

Context

Companion to dotnet/msbuild#13609, which adds a new per-task telemetry event build/tasks/details emitted from BuildManager. The MSBuild PR motivates this work: we want richer task-execution data (per-task name, executions count, task host runtime, etc.) so we can use real-world frequency data to drive decisions about which built-in tasks to prioritize / optimize.

The event carries:

• TaskCount — number of distinct tasks in the payload (capped at 100).
• TotalTaskCount — total number of distinct tasks observed.
• Tasks — JSON array of task-detail records (top 100 by ExecutionsCount), ready for Kusto mv-expand.

Changes

src/Cli/dotnet/Commands/MSBuild/MSBuildLogger.cs:

• Added TasksDetailsTelemetryEventName = "build/tasks/details" constant.
• Added a case in FormatAndSend that pass-through-forwards the event under the msbuild/ namespace, with no hashed properties (the payload is already a JSON string with no PII).

Unlike the existing build/tasks / build/tasks/taskfactory events, this event is not aggregated client-side — MSBuild already does the aggregation/capping (top 100, hashed custom-task names) and the SDK just relays it.

Testing

• New test ItForwardsTaskDetailsEvent in GivenMSBuildLogger verifies the event is forwarded under the expected name and that all three properties (Tasks, TaskCount, TotalTaskCount) are preserved verbatim.
• All 8 GivenMSBuildLogger tests pass locally.

Rollout

This change is forward-compatible: older MSBuilds simply won't emit the event, and the case in FormatAndSend is a no-op when the event isn't raised. No env-var gating is needed on the SDK side — gating lives in MSBuild (MSBUILDTELEMETRYEXCLUDETASKSDETAILS / Traits.ExcludeTasksDetailsFromTelemetry).

[Copilot]

Pull request overview

This PR updates the .NET SDK’s MSBuild logger to forward a new MSBuild telemetry event (build/tasks/details) under the msbuild/ namespace, enabling richer per-task execution telemetry to flow through the CLI telemetry pipeline.

Changes:

• Add TasksDetailsTelemetryEventName = "build/tasks/details" and forward it via MSBuildLogger.FormatAndSend as msbuild/build/tasks/details without hashing.
• Add a new unit test verifying the event name and that Tasks, TaskCount, and TotalTaskCount are preserved verbatim.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Cli/dotnet/Commands/MSBuild/MSBuildLogger.cs	Adds a constant and a FormatAndSend switch case to forward build/tasks/details as msbuild/build/tasks/details.
test/dotnet.Tests/CommandTests/MSBuild/GivenMSBuildLogger.cs	Adds a test validating forwarding behavior and property preservation for the new telemetry event.