Thread cancellation through 5 PostgreSQL web reads (#4203)

[erikdarlingdata]

Refs #4203.

Why

An abandoned web request for a PostgreSQL-target read still ran its store query to completion, because these five tools took no CancellationToken and could not stop a query the caller had already given up on.

What changes

Five tools under Darling/PerformanceMonitor.Darling.Service/Mcp/ now take a trailing CancellationToken cancellationToken = default and pass it into every store call they make (resolver, coverage/precondition checks, the row reads, not-collected status), following the pattern of #4357/#4359:

• DarlingMcpPgIndexTools.cs — get_pg_index_bloat, get_pg_column_stats
• DarlingMcpPgCpuUtilizationTools.cs — get_pg_cpu_utilization
• DarlingMcpPgLogEventTools.cs — get_pg_log_events
• DarlingMcpPgLoggingAuditTools.cs — get_pg_logging_audit

Each tool's catch block is narrowed to when (ex is not OperationCanceledException). All five storage-layer methods these tools call already accepted a CancellationToken parameter, so no shared-helper signature changed.

The five tools are removed from DarlingWebEndpoints.CancellationAllowlist, and their dispatch entries now pass cancellationToken: c.RequestAborted (or the equivalent positional argument for the get_pg_cpu_utilization/get_pg_index_bloat/get_pg_column_stats/get_pg_log_events calls).

Lite: N/A, no /api/read surface exposes these tools.

Test plan

• dotnet build Darling/Darling.Tests/Darling.Tests.csproj -p:EnableWindowsTargeting=true — 0 warnings-relevant errors, 0 errors.
• dotnet build Lite.Tests/Lite.Tests.csproj -p:EnableWindowsTargeting=true — 0 errors (both build-only on macOS; Windows-only, CI decides them at runtime).
• Ran WebReadCancellationPinTests in-process on macOS: Total: 127, Errors: 0, Failed: 0. This is a reflection ratchet over every non-allowlisted dispatch entry (EveryStoreReadingToolMethod_TakesACancellationToken_UnlessAllowlisted, CancellationAllowlist_HasNoStaleEntry); before this change these 5 tools were still on the allowlist with no CancellationToken parameter, so the ratchet passed them by construction (RED case: had one of the five been removed from the allowlist without adding the parameter and dispatch argument, EveryStoreReadingToolMethod_TakesACancellationToken_UnlessAllowlisted would fail on that dispatch entry for dropping c.RequestAborted).
• Also ran PgTargetMcpSurfaceTests (3/3), McpServiceParameterDiSeatCensusTests (1/1) in-process — both green. EngineCapabilityMissTests and RuntimePreconditionMissTests were not found as test classes in this assembly (0 discovered), so nothing to run there.

CHANGELOG entry

SECTION: Fixed
ENTRY:

• Web reads for PostgreSQL index bloat, column stats, CPU utilization, log events and logging audit now honour request cancellation ([Thread cancellation through 5 PostgreSQL web reads (#4203) #4409]) - an abandoned web request for one of these five reads previously ran its underlying store query to completion instead of stopping; each now threads the request's cancellation token through every store call.
  REF:
  [Thread cancellation through 5 PostgreSQL web reads (#4203) #4409]: Thread cancellation through 5 PostgreSQL web reads (#4203) #4409