docs(dotnet): Document MSBuild Sentry CLI usage when building with Docker

[jamescrosswell]

DESCRIBE YOUR PR

Adds a new "Building with Docker" section to the .NET MSBuild setup page, addressing the two Docker-specific gotchas documented in getsentry/sentry-dotnet#2420:

• Auth token — how to pass SENTRY_AUTH_TOKEN securely as a docker build --build-arg, promote it to an ENV var in the build stage, and why both ARG and ENV are required.
• Multi-stage Dockerfiles — how to disable Sentry CLI in the dotnet publish stage with -p:UseSentryCLI=false to avoid failures when project source isn't present in the publish context.

Also adds a brief pointer to this new section from the existing CI/CD authentication bullet, so users reading about server builds are directed to the Docker guidance.

A complete multi-stage Dockerfile example (ASP.NET Core 8.0) is included.

Fixes getsentry/sentry-dotnet#2420

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PRE-MERGE CHECKLIST

• Checked Vercel preview for correctness, including links
• PR was reviewed and approved by any necessary SMEs (subject matter experts)
• PR was reviewed and approved by a member of the Sentry docs team

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Project	Deployment	Actions	Updated (UTC)
develop-docs	Ready	Preview, Comment	Jul 9, 2026 1:07pm
sentry-docs	Ready	Preview, Comment	Jul 9, 2026 1:07pm

[Flash0ver]

🤘

[Flash0ver]

note: technically, --no-build also implicitly sets the --no-restore flag, but I personally also prefer explicitness

[sentry]

Bug: The documentation overstates that # syntax=docker/dockerfile:1 "ensures" support for the env= option. This is not guaranteed for users with stale, cached Docker frontend images.
_{Severity: LOW}

Suggested Fix

To improve accuracy, pin the Dockerfile syntax to a specific version that supports the env= feature, such as # syntax=docker/dockerfile:1.10. Alternatively, rephrase the documentation to clarify that docker/dockerfile:1 points to the latest stable version 1 syntax and that modern Docker installations are required for the env= feature to be available.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: docs/platforms/dotnet/common/configuration/msbuild.mdx#L283

Potential issue: The documentation states that using the `# syntax=docker/dockerfile:1`
directive "ensures" the Docker frontend supports the `env=` option for secrets. However,
`docker/dockerfile:1` is a floating tag. A user with a stale, cached version of this
image from before v1.10 (which introduced `env=`) could experience a build failure.
While this scenario is unlikely in practice, as most users will pull a recent version of
the image, the documentation's claim is technically inaccurate and could be misleading
in rare edge cases.

Also affects:

• docs/platforms/dotnet/common/configuration/msbuild.mdx:312~312