Avoid eager trace payload construction when diagnostics are disabled

[berndverst]

Summary

• guard TraceHelper factory, format, and exception payload construction with the matching EventSource level check
• defer orchestration runtime-state serialization, decision joins, and Service Bus batch formatting until diagnostics are enabled
• add regression coverage proving factories and formatting are skipped when disabled, execute exactly once when enabled, and preserve event IDs, schemas, event types, messages, and exception return values

Compatibility and performance

This does not change public APIs or EventSource event IDs/schemas. Enabled diagnostic payloads remain unchanged. When the requested level is disabled, high-throughput dispatch paths now avoid runtime-state serialization, LINQ enumeration, string.Join, interpolation, and final formatting allocations.

Validation

• dotnet test Test\DurableTask.Core.Tests\DurableTask.Core.Tests.csproj -f net8.0 --filter "FullyQualifiedName~TraceHelperTests|FullyQualifiedName~CommonTests.ShouldValidateEventSource"
• dotnet test Test\DurableTask.Core.Tests\DurableTask.Core.Tests.csproj -f net48 --filter "FullyQualifiedName~TraceHelperTests|FullyQualifiedName~CommonTests.ShouldValidateEventSource"
• dotnet build src\DurableTask.ServiceBus\DurableTask.ServiceBus.csproj

Fixes #1377

[Copilot]

Pull request overview

This PR improves tracing performance by ensuring expensive diagnostic payload construction (factories, formatting, exception payload strings, runtime-state serialization, batch joins) is deferred until the corresponding EventSource level is actually enabled, keeping enabled payloads/events unchanged.

Changes:

• Add an internal DefaultEventSource.Log.IsEventEnabled(TraceEventType) helper and use it to early-return from TraceHelper factory/format/exception helpers when disabled.
• Update high-throughput call sites (orchestration dispatcher + Service Bus) to wrap expensive formatting inside Func<string> so work is skipped when diagnostics are off.
• Add regression tests intended to verify factories/formatting are skipped when disabled and run exactly once when enabled (note: current test file location likely prevents execution in CI on case-sensitive filesystems).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Test/DurableTask.Core.Tests/TraceHelperTests.cs	Adds regression tests for lazy factory/format/exception payload evaluation (currently placed under legacy Test/ tree).
src/DurableTask.Core/Tracing/TraceHelper.cs	Adds level guards to prevent eager payload construction for factory/format/exception helpers.
src/DurableTask.Core/Tracing/DefaultEventSource.cs	Introduces IsEventEnabled(TraceEventType) to map trace levels to EventSource enablement checks.
src/DurableTask.Core/TaskOrchestrationDispatcher.cs	Defers runtime-state serialization and decision formatting behind Func<string> (only when enabled).
src/DurableTask.ServiceBus/ServiceBusOrchestrationService.cs	Defers batch/message formatting (string.Join, LINQ, etc.) behind Func<string> (only when enabled).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[cgillum]

This is a nice improvement. One caveat, however, is that I think Windows App Service-hosted apps capture all ETW trace levels by default, which means we won't observe improvements for those apps. However, I expect this will help with anything hosted on Linux or outside of App Service.