Plan analysis: mark which warnings are SQL Server's and key duplicate index suggestions on the database (#4520, #4523)

[erikdarlingdata]

Fixes #4520
Fixes #4523
Part of #4511

Why

Two small syncs from PerformanceStudio's plan analyzer.

PlanWarning carried nothing but type, severity and message, so a reader could not tell a warning SQL Server itself wrote into the plan (a spill, an implicit conversion, no statistics — a record of what the engine did) apart from one the analyzer inferred from plan shape (which can be wrong about a particular plan in a way the engine's own record cannot be).

Rule 30's duplicate-index-suggestion check grouped missing index suggestions by schema and table only. A plan touching a same-named table (e.g. dbo.t) in two different databases had its suggestions merged and reported as duplicates of each other, even though they target unrelated tables.

What changes

• PlanWarning.Source (new enum PlanWarningSource: Analyzer default, SqlServer). ShowPlanParser.ParseWarningsFromElement stamps every warning it returns as SqlServer in one place — the only place parser warnings are built — so a new engine warning is attributed correctly without anyone needing to remember it at each construction site.
• The MCP plan-analysis JSON now carries a source field on every warning (additive; existing fields unchanged).
• The plan viewer tags the engine's own warnings with [SQL Server] next to the warning type, in both the statement-level and node-level warnings panels. Only the engine's are tagged, since they are the minority and a badge on every line would carry no information.
• Rule 30's duplicate-index grouping key and the per-suggestion lookup key now include the database (MissingIndex.Database, which already existed on the model), not just schema and table.

Test plan

New Darling.Tests classes with synthetic plan XML (dbo.t, [db1]/[db2]):

• PlanSync4520Tests: an engine PlanAffectingConvert warning is stamped SqlServer; an analyzer non-SARGable-predicate warning keeps the default Analyzer; the MCP formatter's JSON carries both source values on the product's own formatting call path (McpPlanAnalysisFormatter.BuildAnalysisResult).

• PlanSync4523Tests: two missing-index suggestions for the same table name in two different databases are NOT reported as duplicates; two suggestions for the same table in the same database still are.

• Findings do not say whether SQL Server or the analyzer produced them (PlanWarning.Source) #4520: PlanWarning.Source and PlanWarningSource are new, so PlanSync4520Tests is a compile-only RED on dev. Mutation: removing the parser's Source = SqlServer stamping fails EngineWarning_IsStampedSqlServer (Expected: SqlServer, Actual: Analyzer) and McpFormatter_CarriesSourceOnEachWarning ("source":"SqlServer" not found).

• Duplicate index suggestions (rule 30) treat same-named tables in different databases as one table #4523: SameTableName_DifferentDatabases_AreNotReportedAsDuplicates is a runtime RED on dev (Assert.DoesNotContain() Failure: Filter matched in collection). Mutation: dropping the database from both rule-30 keys fails it again.

• Run: the new classes plus the plan-analysis classes (ShowPlanParserCondAndMultiplePlanTests, the ActualPlan* classes, QueryModificationDetectorTests, ReproScriptBuilderHardeningTests, DarlingAnalysisPipelineTests, DarlingMcpPlanToolsSurfaceAndSqlTests, McpPlanAnalysisEnvelopeTests, SerialLoopStoreSizeSourceTests, TsqlConventionGuardTests, DocCommentHygieneTests): Total: 234, Failed: 0. McpPlanAnalysisEnvelopeTests needed no change: the source field is additive. The live-Postgres plan-tool class runs in CI. Lite.Tests builds; its plan classes run on Windows only.

• Consumers checked: PlanAdvisoryAggregator reads severity and counts only; McpPlanAnalysisFormatter gains source; the plan viewer tags the engine's own warnings [SQL Server] in both warning panels, as PerformanceStudio does. PerformanceStudio's CLI text formatter has no PM counterpart.

CHANGELOG

SECTION: Added
ENTRY: - Plan analysis now marks which findings are SQL Server's own warnings and which are inferences, and duplicate missing-index suggestions are no longer merged across different databases ([#4543]) - PlanWarning.Source says whether a plan warning came from the engine's own <Warnings> element or from the analyzer; the plan viewer tags the engine's with [SQL Server] and the MCP plan tools carry it as a source field. Rule 30's duplicate-index-suggestion check now keys on database as well as schema and table, so same-named tables in different databases are no longer reported as duplicates of each other.
REF: [#4543]: #4543