Update AppContext Switch Docs

[paulmedynski]

MDS AppContext Switches are documented here:

https://learn.microsoft.com/en-us/sql/connect/ado-net/appcontext-switches?view=sql-server-ver16

That page lists the following switches:

• DisableTNIRByDefaultInConnectionString
• EnableRetryLogic
• LegacyRowVersionNullBehavior
• MakeReadAsyncBlocking
• SuppressInsecureTLSWarning
• TruncateScaledDecimal
• UseManagedNetworkingOnWindows
• UseOneSecFloorInTimeoutCalculationDuringLogin
• UseSystemDefaultSecureProtocols

Those don't match the current code, which supports the following switches:

• DisableTNIRByDefaultInConnectionString
• LegacyRowVersionNullBehavior
• LegacyVarTimeZeroScaleBehaviour
• MakeReadAsyncBlocking
• SuppressInsecureTLSWarning
• TruncateScaledDecimal
• UseCompatibilityAsyncBehaviour
• UseCompatibilityProcessSni
• UseConnectionPoolV2
• UseOneSecFloorInTimeoutCalculationDuringLogin
• UseManagedNetworkingOnWindows

Update the public docs to match reality, and find any other public docs that may also be inaccurate (README, BUILDGUIDE, etc).

[federico-paganini]

I'd like to take this one — please assign it to me.

The drift has widened since the OP: the page (last touched 2026-08) documents ~11 switches, while current main's LocalAppContextSwitches.cs carries 16+. Missing at least:

• UseLegacyIdleTimeoutBehavior (default true) — gates whether Connection Idle Timeout (Add configurable idle connection timeout (ADO #39970) #4295, 7.1.0-preview2) is enforced at all; with the switch at its default the keyword parses but changes nothing.
• UseConnectionPoolV2 (default false) — selects ChannelDbConnectionPool over the v1 pool.
• LegacyVarTimeZeroScaleBehaviour (default true)
• UseLegacyFailoverAlternationOnLoginSqlErrors (default false)
• UseOverallConnectTimeoutForPoolWait (default false)

Plan: a PR against MicrosoftDocs/sql-docs adding the missing sections in the page's existing format (defaults and semantics taken from the source), plus one cross-cutting note the page currently doesn't state anywhere: switch values are cached in statics on first read, so setting a switch after the first use of any SqlClient type is a silent no-op — we verified that empirically while validating #4295 (details in the #3667 thread).

[federico-paganini]

PR is up: MicrosoftDocs/sql-docs#10381 — adds the five missing switches (sections in the page's existing format, defaults and introduction versions verified against LocalAppContextSwitches.cs and the release tags) plus a cross-cutting note that switch values are latched on first read.

Two entries from the code-side inventory turned out not to belong on the page, for anyone auditing this later: UseMinimumLoginTimeout is a property name whose switch string is the already-documented UseOneSecFloorInTimeoutCalculationDuringLogin, and GlobalizationInvariantMode reads the runtime's System.Globalization.Invariant switch rather than a SqlClient one.