Quarantine flaky pipeline tests; add triage prompt

[paulmedynski]

Description

Quarantines two intermittently-failing tests observed in the public CI pipelines on main at/after commit bf4cd14, and adds a reusable prompt for triaging pipeline test failures.

Test changes (engineering processes / test coverage):

• SimulatedServerTests.ConnectionTests.TransientFault_RetryEnabled_ShouldSucceed_Async — under CI load the simulated transient error occasionally resurfaces on the retry login, so the async open propagates the SqlException instead of succeeding. Same transient-fault retry-timing family as its already-quarantined siblings. Marked [Trait("Category", "flaky")] with the observed failure signature.
• ConnectionPoolTest.TransactionPoolTest.TransactionCleanupTest — the process-global pool (keyed by connection string) intermittently reports one extra connection (Assert.Equal Expected 2, Actual 3) due to cross-test contamination while running inside a TransactionScope. It is a test-isolation / pool-count race, not a product defect. Marked [Trait("Category", "flaky")] with an accurate root-cause comment.

Tooling:

• Adds .github/prompts/triage-pipeline-failures.prompt.md — an access-agnostic (ADO MCP / az CLI / REST) workflow to find and classify failing tests in the SqlClient pipelines at/after a given commit, capture full xUnit output/stack traces, distinguish regression vs pre-existing, and present findings for approval before fixing or quarantining.

No product code changes; no public API changes.

[Copilot]

Pull request overview

Quarantines two intermittently failing tests in the SqlClient CI by marking them with the existing Category=flaky trait, and adds a reusable Copilot prompt to triage pipeline test failures at/after a specific commit SHA.

Changes:

• Mark TransientFault_RetryEnabled_ShouldSucceed_Async (simulated server unit test) as quarantined via [Trait("Category", "flaky")] with an embedded failure signature comment.
• Mark TransactionCleanupTest (manual pooling test) as quarantined via [Trait("Category", "flaky")] with an embedded failure signature comment.
• Add .github/prompts/triage-pipeline-failures.prompt.md to guide ADO/GitHub pipeline failure investigation and classification workflows.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/Microsoft.Data.SqlClient/tests/UnitTests/SimulatedServerTests/ConnectionTests.cs	Quarantines an intermittently failing transient-retry simulated-server test.
src/Microsoft.Data.SqlClient/tests/ManualTests/SQL/ConnectionPoolTest/TransactionPoolTest.cs	Quarantines an intermittently failing transaction-pool cleanup test.
.github/prompts/triage-pipeline-failures.prompt.md	Adds a triage workflow prompt for classifying pipeline test failures and deciding fix vs quarantine.

Comments suppressed due to low confidence (1)

src/Microsoft.Data.SqlClient/tests/ManualTests/SQL/ConnectionPoolTest/TransactionPoolTest.cs:93

• Quarantining this test as [Trait("Category", "flaky")] reduces regular CI coverage, but the described failure mode (pool ConnectionCount off by 1) can be made deterministic by isolating the pool key per invocation. Since pools are process-global and keyed by connection string, appending a unique ApplicationName (via SqlConnectionStringBuilder) prevents cross-test contamination without quarantining the test.

        [Trait("Category", "flaky")]
        [ConditionalTheory(typeof(DataTestUtility), nameof(DataTestUtility.AreConnStringsSetup), nameof(DataTestUtility.IsNotAzureSynapse))]
        [ClassData(typeof(ConnectionPoolConnectionStringProvider))]
        public static void TransactionCleanupTest(string connectionString)
        {

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.70%. Comparing base (d040700) to head (b8bc2d3).
⚠️ Report is 4 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (d040700) and HEAD (b8bc2d3). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (d040700)	HEAD (b8bc2d3)
CI-SqlClient	1	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4476      +/-   ##
==========================================
- Coverage   70.88%   62.70%   -8.19%     
==========================================
  Files         288      283       -5     
  Lines       43935    66821   +22886     
==========================================
+ Hits        31142    41898   +10756     
- Misses      12793    24923   +12130     

Flag	Coverage Δ
CI-SqlClient	?
PR-SqlClient-Project	62.70% <ø> (?)

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.