fix: resolve flaky integration test timing issues

- GCSamplerV2 tests: add Gen0-only GC.Collect(0) calls so the V2
  per-generation subtraction logic reliably reports non-zero Gen0
  collections regardless of startup timing.

- OTel metrics tests: wait for the OTLP export log line (fires every
  5s) instead of analytic_event_data (fires at ~60s), which races
  with the 60-second WaitForLogLine timeout on slow CI machines.

- OTel stress tests: replace the 60s analytics wait + 45s Thread.Sleep
  with a wait for 3 OTLP exports (~15s), cutting exercise time from
  ~123s to ~20s.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: tippmar-nr

tests/Agent/IntegrationTests/IntegrationTests/OpenTelemetry/OpenTelemetryMetricsTests.cs

@@ -35,8 +35,9 @@ protected OpenTelemetryMetricsTestsBase(TFixture fixture, ITestOutputHelper outp
             {
                 _fixture.AgentLog.WaitForLogLine(AgentLogFile.AgentConnectedLogLineRegex, TimeSpan.FromMinutes(1));
 
-                // otlp metrics export will be complete before the first analytics event harvest
-                _fixture.AgentLog.WaitForLogLine(AgentLogFile.AnalyticsEventDataLogLineRegex, TimeSpan.FromMinutes(1));
+                // Wait for actual OTLP metrics export (every 5s) rather than the analytics event
+                // harvest (every 60s), which can race with the WaitForLogLine timeout on slow CI.
+                _fixture.AgentLog.WaitForLogLine(AgentLogFile.OtlpMetricsExportedLogLineRegex, TimeSpan.FromMinutes(1));
 
                 _otlpSummaries = _fixture.GetCollectedOTLPMetrics();
             }

tests/Agent/IntegrationTests/IntegrationTests/OpenTelemetry/OpenTelemetryStressTests.cs

@@ -40,12 +40,10 @@ protected OpenTelemetryStressTestsBase(TFixture fixture, ITestOutputHelper outpu
                 _fixture.TestLogger.WriteLine($"Agent Log Path: {_fixture.AgentLog?.FilePath}");
                 _fixture.AgentLog.WaitForLogLine(AgentLogFile.AgentConnectedLogLineRegex, TimeSpan.FromMinutes(2));
 
-                // Wait for workload to complete - give more time for all metrics to be collected
-                _fixture.AgentLog.WaitForLogLine(AgentLogFile.AnalyticsEventDataLogLineRegex, TimeSpan.FromMinutes(5));
-
-                // Add extra delay to ensure all metrics are exported
-                // Increased from 30 to 45 seconds for slower CI environments
-                System.Threading.Thread.Sleep(TimeSpan.FromSeconds(45));
+                // Wait for at least 3 OTLP exports (every 5s) to ensure sufficient metric data.
+                // This replaces a 60s analytic_event_data wait + 45s Thread.Sleep that added
+                // ~105s of unnecessary delay.
+                _fixture.AgentLog.WaitForLogLines(AgentLogFile.OtlpMetricsExportedLogLineRegex, TimeSpan.FromMinutes(2), 3);
 
                 // Don't specify exact count - just get what's available with a reasonable max
                 _otlpSummaries = _fixture.GetCollectedOTLPMetrics(count: 1000);

tests/Agent/IntegrationTests/SharedApplications/Common/MultiFunctionApplicationHelpers/NetStandardLibraries/PerformanceMetrics.cs

@@ -35,6 +35,13 @@ private static void StartAgent()
         // We need atleast one known GC invocation to verify our GC metrics.
         GC.Collect();
 
+        // Gen0-only collections ensure the GCSamplerV2's per-generation counting
+        // (which subtracts higher-gen counts from lower-gen counts) reports non-zero
+        // Gen0 collections. Without these, a full GC.Collect() increments all generation
+        // counters equally, and the subtraction can yield zero on fast-starting processes.
+        GC.Collect(0);
+        GC.Collect(0);
+
         // Get everything started up and time for initial Sample().
         Thread.Sleep(TimeSpan.FromSeconds(10));
     }