docs(dotnet): Document RecordTransaction for already-completed transactions

[jamescrosswell]

DESCRIBE YOUR PR

Documents the new SentrySdk.RecordTransaction API from getsentry/sentry-dotnet#5333, which records transactions and spans that already completed elsewhere (e.g. work measured on another machine and replayed through a proxy) with explicit start timestamps and durations.

• Adds a new Record Already-Completed Transactions section as the third section of the .NET custom instrumentation page, via a new platform-includes/performance/record-completed-transactions/dotnet.mdx include.
• Covers the differences from StartTransaction: explicit timing, sampling skipped (BeforeSendTransaction still runs), and clean-scope capture with ConfigureScope for attaching origin-trace data.

Note: the version alert says 6.8.0 — the SDK PR merged just after the 6.7.0 release cut, so this assumes it ships in the next release. Should be confirmed (and this PR held) until that release is out.

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Project	Deployment	Actions	Updated (UTC)
sentry-docs	Ready	Preview	Jul 16, 2026 8:59am

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[sentry]

Bug: The documentation references version 6.8.0 for a new .NET SDK feature, but this version is tentative and unconfirmed. The feature may ship in a different release.
_{Severity: MEDIUM}

Suggested Fix

Hold the merge of this pull request until the .NET SDK version containing the RecordTransaction feature is officially released. Once the version is confirmed, update the availableSince alert in the documentation to reflect the correct version number.

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: platform-includes/performance/record-completed-transactions/dotnet.mdx#L3

Potential issue: The documentation for the new `RecordTransaction` feature in the .NET
SDK specifies it is available since version `6.8.0`. However, this version number is an
unconfirmed assumption, as noted in the pull request description. Publishing this
documentation before the SDK version is finalized could lead to users on version `6.8.0`
not finding the API if it ships later, or users on earlier versions encountering runtime
errors. This will likely cause user confusion and support tickets.

_{Did we get this right? 👍 / 👎 to inform future reviews.}