Seed CLI telemetry session IDs from CI workflow context

[Copilot]

The CLI had a per-process telemetry session ID, but no first-class way to correlate multiple dotnet invocations that belong to the same CI workflow. This updates the CLI to honor DOTNET_CLI_TELEMETRY_SESSIONID as the initial session seed and documents how CI integrations can set it consistently.

• CLI session seeding

  • TelemetryClient now uses DOTNET_CLI_TELEMETRY_SESSIONID when no explicit session ID is provided.
  • This preserves existing explicit-session behavior while enabling cross-invocation correlation for workflow-scoped sessions.

• MSBuild forwarding coverage

  • Added focused tests to verify:
    • environment-seeded session IDs become TelemetryClient.CurrentSessionId
    • explicit session IDs still take precedence
    • forwarded MSBuild invocations receive the seeded DOTNET_CLI_TELEMETRY_SESSIONID

• Docs

  • Documented DOTNET_CLI_TELEMETRY_SESSIONID in telemetry docs and CLI README.
  • Added concrete GitHub Actions and Azure DevOps examples showing how to stamp a workflow/job-scoped identifier once and let subsequent dotnet invocations inherit it.

• Repo CI integration

  • Repo GitHub Actions workflow now sets:

    DOTNET_CLI_TELEMETRY_SESSIONID: gha-${{ github.repository_id }}-${{ github.run_id }}-${{ github.run_attempt }}

  • Repo AzDo pipelines now set:

    DOTNET_CLI_TELEMETRY_SESSIONID: azdo-$(System.CollectionId)-$(System.TeamProjectId)-$(Build.BuildId)

Example:

var initialSessionId = !string.IsNullOrEmpty(sessionId)
    ? sessionId
    : environmentProvider.GetEnvironmentVariable(EnvironmentVariableNames.DOTNET_CLI_TELEMETRY_SESSIONID);

CurrentSessionId ??= !string.IsNullOrEmpty(initialSessionId)
    ? initialSessionId
    : Guid.NewGuid().ToString();

[Copilot]

Pull request overview

This PR updates the .NET SDK CLI telemetry implementation to allow CI systems to correlate multiple dotnet invocations by seeding the in-process telemetry session ID from DOTNET_CLI_TELEMETRY_SESSIONID, and adds test/doc/CI updates to support that workflow.

Changes:

• Seed TelemetryClient.CurrentSessionId from DOTNET_CLI_TELEMETRY_SESSIONID when no explicit session ID is provided.
• Add/adjust tests to validate environment seeding, explicit session ID precedence, and MSBuild forwarding behavior.
• Document the new environment variable and set it in selected CI YAML definitions.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Cli/dotnet/Telemetry/TelemetryClient.cs	Seeds session ID from DOTNET_CLI_TELEMETRY_SESSIONID before falling back to GUID generation.
test/dotnet.Tests/TelemetryTests/TelemetryClientTests.cs	Adds unit coverage for environment-seeded vs explicit session ID behavior; serializes tests touching static telemetry state.
test/dotnet.Tests/CommandTests/MSBuild/GivenMsbuildForwardingApp.cs	Adds coverage ensuring MSBuild forwarding propagates the seeded telemetry session ID.
documentation/project-docs/telemetry.md	Documents DOTNET_CLI_TELEMETRY_SESSIONID and clarifies session ID may be non-GUID correlation identifiers.
src/Cli/dotnet/README.md	Adds DOTNET_CLI_TELEMETRY_SESSIONID to CLI environment variable documentation.
.github/workflows/copilot-setup-steps.yml	Sets DOTNET_CLI_TELEMETRY_SESSIONID in the Copilot setup workflow environment.
.vsts-pr.yml	Sets DOTNET_CLI_TELEMETRY_SESSIONID in AzDO PR pipeline variables.
.vsts-ci.yml	Sets DOTNET_CLI_TELEMETRY_SESSIONID in AzDO CI pipeline variables.

[github-actions]

Due to lack of recent activity, this PR has been labeled as 'Stale'. It will be closed if no further activity occurs within 7 more days. Any new comment will remove the label.

[baronfel]

@copilot please fix the merge conflicts in this pull request.

[Copilot]

@copilot please fix the merge conflicts in this pull request.

Fixed by merging origin/main and resolving the conflicts in TelemetryClientTests and GivenMsbuildForwardingApp in commit bb97748.

[marcpopMSFT]

Only question I have is how do we ensure future yml changes end up including this change. Should we update a doc somewhere so copilot sees that when adding/editing yml in the future? Can be a separate PR.

[marcpopMSFT]

Another thought I had was how to get this into arcade so we seed the session id for all our repo builds. Not sure how to seed it into all workflows as those don't go through arcade.

[baronfel]

Only question I have is how do we ensure future yml changes end up including this change. Should we update a doc somewhere so copilot sees that when adding/editing yml in the future? Can be a separate PR.

Good thought - will poke an agent/get a note into our reviewer docs/skills.

Another thought I had was how to get this into arcade so we seed the session id for all our repo builds. Not sure how to seed it into all workflows as those don't go through arcade.

Also a great idea - will log an issue for this at the arcade repo for discussion.