MSBuild Release Orchestration

This skill guides an agent through the MSBuild release process defined in documentation/release-checklist.md. The checklist is the single source of truth — this skill provides context on how to execute it.

Overview

MSBuild is a component that gets inserted into Visual Studio. VS ships monthly; MSBuild must branch and prepare its bits before VS is ready to take them. See the release process doc for the full timeline diagram.

The insertion pipeline routes MSBuild branches to VS branches:

• main → VS main (daily canary)
• vs* release branch → VS main (replaces main → main after branch snap)

VS handles the progression from main → rel/insiders → rel/stable on its own schedule. MSBuild's responsibility is to have final-branded bits in VS main before the insiders snap date.

Each monthly VS release produces:

• A new vs* branch from main
• Final branding on that branch
• A version bump in main
• DARC channel/subscription updates
• A VS insertion
• Post-GA publishing to nuget.org and docs

The process is organized into 6 timeline-gated phases (0–5), each with an explicit trigger.

Execution model: This skill is designed for an interactive Copilot session. The agent walks through each phase step-by-step, but every command that modifies state (git push, DARC writes, pipeline changes, PR creation) requires user approval before execution. Read-only queries (DARC get-*, git log, etc.) can run without approval.

Required Inputs

Before starting any phase, ensure you have these values (the user must provide them — version increments are irregular and cannot be computed):

Version examples above track the current cycle (eng/Versions.props VersionPrefix is 18.10.0). Dates are intentionally shown as a format only — always read the real ones from the VS-Dates wiki.

How to determine PACKAGE_VALIDATION_BASELINE_VERSION

The value is the latest {{THIS_RELEASE_VERSION}}.0-preview-NNNNN-NN MSBuild package that is both:

1. Published on the public dotnet-tools feed — this is the feed the official build publishes to and that ApiCompat restores baselines from. If the version isn't here, ApiCompat fails with NU1102.
2. Produced from a commit reachable from vs{{THIS_RELEASE_VERSION}} — i.e. a commit on vs{{THIS_RELEASE_VERSION}}, or the main commit vs{{THIS_RELEASE_VERSION}} was branched from.

Two tempting wrong answers — and why they're wrong:

Procedure: run the helper — it does the whole resolution mechanically (requires az login with devdiv access):

pwsh ./scripts/Get-PackageValidationBaseline.ps1 -ThisReleaseVersion {{THIS_RELEASE_VERSION}}
# -> prints e.g. 18.9.0-preview-26330-01

It computes git merge-base origin/main origin/vs{{THIS_RELEASE_VERSION}}, finds the matching successful build in pipeline 9434, derives the package version from the OfficialBuildId, and verifies it on the dotnet-tools feed. If it fails, read the script's own .DESCRIPTION header for the manual equivalent rather than reproducing it here.

Prerequisites

• gh cli
• az cli
• darc cli — Arcade enforces a minimum version; if darc refuses with a "below the minimum required version" error, run .\eng\common\darc-init.ps1

Phase Summary

DARC Batching

DARC write commands push to the maestro-configuration repo. Batch related changes into one PR:

1. Choose a branch name like release/msbuild-{{THIS_RELEASE_VERSION}}
2. Add --configuration-branch <name> --no-pr to every write command except the last
3. Last command: use --configuration-branch <name> without --no-pr to create the PR
4. Get the PR reviewed and merged

Read-only commands (get-default-channels, get-subscriptions, get-channel) don't need these flags.

Non-interactive (-q). darc add-default-channel / add-subscription prompt y/n when the target branch does not exist yet (e.g. pre-creating the vs{{NEXT_VERSION}} mapping in Phase 1.2c, or adding the new vs{{THIS_RELEASE_VERSION}} backflow in Phase 2). Console input is redirected in an agent session, so the prompt fails the command — always pass -q for these "branch doesn't exist yet" writes.

Phase 2 — what moves vs. what stays. When rotating main to the next channel, retarget only the subscriptions whose target branch is main (dotnet/dotnet @ main, dotnet/fsharp @ main). Never retarget a subscription that targets a VMR servicing/release branch (dotnet/dotnet @ release/*) — that includes the SDK band paired with the new vs{{THIS_RELEASE_VERSION}} branch and any .NET-next preview band (release/*-preview*). Those stay on VS {{THIS_RELEASE_VERSION}} so the new release branch owns their downstream flow; moving them steals it. (This bit the 18.9 release: the band and preview subs were moved and had to be reverted.)

Phase 2 — VMR backflow rotation (easy to miss). Backflow (dotnet/dotnet → msbuild, source-enabled) must rotate too when the new vs{{THIS_RELEASE_VERSION}} is paired with an SDK band (skip for a VS-only release): repoint the → main backflow to the next SDK band channel (.NET <NEXT_BAND> SDK, the channel dotnet/dotnet @ main publishes to), and add a backflow from the outgoing band channel into the new vs{{THIS_RELEASE_VERSION}} branch (mirror the prior release branch's backflow, e.g. vs18.0 ← .NET 10.0.1xx SDK). See checklist steps 2.2b / 2.3f / 2.3g.

Executing a Phase

When asked to execute a specific phase:

1. Read the full phase from documentation/release-checklist.md
2. Verify the trigger condition is met (previous phases completed)
3. Execute steps in order — respect sequential/parallel annotations
4. For DARC commands: batch writes into one configuration PR per phase
5. Record all output URLs in the tracking issue's artifact table
6. Mark checkboxes as completed in the tracking issue
7. In Phase 5: if documentation/wiki/ChangeWaves.md is changed for this release, update the public Learn page at https://learn.microsoft.com/en-us/visualstudio/msbuild/change-waves?view=visualstudio (or track the required update with an explicit issue/link in the release artifacts).

Key Files

Validation

After completing all phases, verify:

1. Branch vs{{THIS_RELEASE_VERSION}} exists and has final branding
2. Main has VersionPrefix = {{NEXT_VERSION}}.0
3. DARC: main → VS {{NEXT_VERSION}} channel, release branch → VS {{THIS_RELEASE_VERSION}} channel
4. VS insertion PR merged
5. Packages published to nuget.org
6. GitHub release created with tag v{{THIS_RELEASE_EXACT_VERSION}}
7. If documentation/wiki/ChangeWaves.md is changed, the corresponding Learn page update at https://learn.microsoft.com/en-us/visualstudio/msbuild/change-waves?view=visualstudio is completed or explicitly tracked

Error Recovery

• Branch already exists: Release was partially started — check the tracking issue for progress
• DARC channel already exists: Safe to continue — add-channel is idempotent
• OptProf fails on first build: Expected — that's why we use main's OptProf data as fallback
• DARC configuration PR conflicts: Rebase the configuration branch on production and force-push

Major Version Releases

If NEXT_VERSION is a new major version (e.g., 18.x → 19.0), additional steps are needed after Phase 5. See release.md for:

• src/Shared/BuildEnvironmentHelper.cs — VS major version constants
• src/Shared/Constants.cs — version constants
• src/Framework/Telemetry/TelemetryConstants.cs — telemetry version