Add performance, testing, logging, Azure Functions, and glossary to AGENTS.md

[lucaspimentel]

Summary of changes

• Add performance optimization patterns, testing guidelines, and logging guidelines to AGENTS.md.
• Add Azure Functions automatic instrumentation setup documentation.
• Add glossary section for common acronyms.
• Bonus: Fix noop pipeline path exclusions to properly skip CI for documentation-only PRs.

Reason for change

Documentation: Document reusable patterns that apply broadly across the tracer codebase:

• Performance patterns for startup code and hot paths (from PR managed loader: refactor for testability, add unit tests #7594)
• Testing patterns for testability and isolation (from PR managed loader: refactor for testability, add unit tests #7594)
• Logging terminology to avoid customer confusion (from PR Update language used in native log messages #7467)
• Azure Functions setup instructions for different hosting scenarios, developer references, and dependency information
• Common acronyms used throughout the repository

CI Optimization: The noop pipeline was not triggering for documentation-only PRs because it uses StartsWith() matching, not glob patterns. The **/CLAUDE.md pattern never matched .claude/CLAUDE.md.

Implementation details

New documentation sections:

• Performance Guidelines: Identifies performance-critical code paths (bootstrap/startup and hot paths)
• Performance Optimization Patterns: Zero-allocation structs, logging best practices, avoiding params arrays
• Testing Patterns: Abstraction-for-testability with examples
• Logging Guidelines: Consistent customer-facing terminology (Datadog SDK, Instrumentation, Continuous Profiler, Datadog.Trace.dll)
• Azure Functions:
  • Setup instructions for Site Extension vs NuGet package
  • Environment variables for Windows and Linux
  • Developer references to docs/development/AzureFunctions.md
  • Testing instructions and sample locations
  • Dependency information about Datadog.Serverless.Compat and agent startup mechanisms
• Glossary: Common acronyms (AAS, APM, ASM, CI, DBM, DSM, IAST, OTEL, RCM, RASP, WAF)

Pipeline fixes:

• Changed **/CLAUDE.md glob to .claude/ prefix (compatible with StartsWith())
• Added .devcontainer/, .vscode/, LICENSE, NOTICE to exclusions

Other changes:

• Fixed .claude/CLAUDE.md relative path reference
• Improved formatting in Coding Style section

Test coverage

N/A - documentation and CI configuration only

[bouwkast]

Did you write these or did AI write these?

Also curious, was this testable somehow to see whether or not the changes here improved the output that the model gives?

Not really blockers just me wondering how these work 😅

[lucaspimentel]

Did you write these or did AI write these?

Good question. I had Claude Code (the cli tool) write them based on work across several sessions. I asked it to keep track of all the changes we were making and why into a file, especially if it generated code and I asked for specific changes, like "do it again but change XYZ to avoid heap allocations." Later I asked it to summarize that into guidelines and add them to AGENTS.md.

Also curious, was this testable somehow to see whether or not the changes here improved the output that the model gives?

I did #7602 yesterday and I also I did more coding work after adding the guidelines in this PR locally, and it does help. For example, when reviewing my changes to the managed loader it is focusing more on performance than it did before. When generating code it is following the new C# syntax suggestion. Also after #7602 is now using our PR template to update my PR descriptions (it generating the description for this PR).

Not really blockers just me wondering how these work 😅

No, I get it. It's all new. So far I only used AI for auto-complete in the IDE, but I started playing with agents recently and I think I'm finally "getting" it. I've enjoyed having Claude Code in a terminal while I work. It's more like pair programming. I write some code and ask AI to review it, or I ask it to generate some code and I review that. It goes both ways 😝

[dd-trace-dotnet-ci-bot]

Execution-Time Benchmarks Report ⏱️

Execution-time results for samples comparing the following branches/commits:

• This PR (7609)
• master

Execution-time benchmarks measure the whole time it takes to execute a program. And are intended to measure the one-off costs. Cases where the execution time results for the PR are worse than latest master results are shown in red. The following thresholds were used for comparing the execution times:

• Welch test with statistical test for significance of 5%
• Only results indicating a difference greater than 5% and 5 ms are considered.

Note that these results are based on a single point-in-time result for each branch. For full results, see the dashboard.

Graphs show the p99 interval based on the mean and StdDev of the test run, as well as the mean value of the run (shown as a diamond below the graph).

gantt
    title Execution time (ms) FakeDbCommand (.NET Framework 4.8) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Bailout
    This PR (7609) - mean (80ms)  : 75, 84
     .   : milestone, 80,
    master - mean (80ms)  : 77, 84
     .   : milestone, 80,

    section Baseline
    This PR (7609) - mean (75ms)  : 71, 79
     .   : milestone, 75,
    master - mean (75ms)  : 71, 79
     .   : milestone, 75,

    section CallTarget+Inlining+NGEN
    This PR (7609) - mean (1,110ms)  : 1048, 1172
     .   : milestone, 1110,
    master - mean (1,122ms)  : 1058, 1186
     .   : milestone, 1122,

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gantt
    title Execution time (ms) FakeDbCommand (.NET Core 3.1) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Bailout
    This PR (7609) - mean (119ms)  : 114, 125
     .   : milestone, 119,
    master - mean (120ms)  : 114, 125
     .   : milestone, 120,

    section Baseline
    This PR (7609) - mean (118ms)  : 114, 123
     .   : milestone, 118,
    master - mean (119ms)  : 115, 123
     .   : milestone, 119,

    section CallTarget+Inlining+NGEN
    This PR (7609) - mean (792ms)  : 766, 818
     .   : milestone, 792,
    master - mean (802ms)  : 782, 821
     .   : milestone, 802,

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gantt
    title Execution time (ms) FakeDbCommand (.NET 6) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Bailout
    This PR (7609) - mean (112ms)  : 108, 117
     .   : milestone, 112,
    master - mean (114ms)  : 109, 119
     .   : milestone, 114,

    section Baseline
    This PR (7609) - mean (111ms)  : 106, 117
     .   : milestone, 111,
    master - mean (113ms)  : 107, 118
     .   : milestone, 113,

    section CallTarget+Inlining+NGEN
    This PR (7609) - mean (829ms)  : 772, 886
     .   : milestone, 829,
    master - mean (838ms)  : 778, 898
     .   : milestone, 838,

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gantt
    title Execution time (ms) FakeDbCommand (.NET 8) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Bailout
    This PR (7609) - mean (104ms)  : 99, 109
     .   : milestone, 104,
    master - mean (104ms)  : 99, 109
     .   : milestone, 104,

    section Baseline
    This PR (7609) - mean (103ms)  : 98, 108
     .   : milestone, 103,
    master - mean (103ms)  : 98, 108
     .   : milestone, 103,

    section CallTarget+Inlining+NGEN
    This PR (7609) - mean (708ms)  : 687, 730
     .   : milestone, 708,
    master - mean (722ms)  : 698, 745
     .   : milestone, 722,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET Framework 4.8) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Bailout
    This PR (7609) - mean (201ms)  : 198, 204
     .   : milestone, 201,
    master - mean (202ms)  : 198, 207
     .   : milestone, 202,

    section Baseline
    This PR (7609) - mean (199ms)  : 194, 204
     .   : milestone, 199,
    master - mean (200ms)  : 193, 206
     .   : milestone, 200,

    section CallTarget+Inlining+NGEN
    This PR (7609) - mean (1,186ms)  : 1119, 1252
     .   : milestone, 1186,
    master - mean (1,213ms)  : 1145, 1282
     .   : milestone, 1213,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET Core 3.1) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Bailout
    This PR (7609) - mean (286ms)  : 280, 292
     .   : milestone, 286,
    master - mean (296ms)  : 284, 308
     .   : milestone, 296,

    section Baseline
    This PR (7609) - mean (284ms)  : 278, 290
     .   : milestone, 284,
    master - mean (288ms)  : 281, 295
     .   : milestone, 288,

    section CallTarget+Inlining+NGEN
    This PR (7609) - mean (954ms)  : 911, 997
     .   : milestone, 954,
    master - mean (981ms)  : 938, 1024
     .   : milestone, 981,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET 6) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Bailout
    This PR (7609) - mean (288ms)  : 284, 292
     .   : milestone, 288,
    master - mean (299ms)  : 288, 310
     .   : milestone, 299,

    section Baseline
    This PR (7609) - mean (291ms)  : 281, 302
     .   : milestone, 291,
    master - mean (301ms)  : 288, 314
     .   : milestone, 301,

    section CallTarget+Inlining+NGEN
    This PR (7609) - mean (1,016ms)  : 975, 1057
     .   : milestone, 1016,
    master - mean (1,053ms)  : 993, 1114
     .   : milestone, 1053,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET 8) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Bailout
    This PR (7609) - mean (278ms)  : 273, 284
     .   : milestone, 278,
    master - mean (295ms)  : 285, 304
     .   : milestone, 295,

    section Baseline
    This PR (7609) - mean (281ms)  : 271, 290
     .   : milestone, 281,
    master - mean (291ms)  : 284, 299
     .   : milestone, 291,

    section CallTarget+Inlining+NGEN
    This PR (7609) - mean (865ms)  : 839, 890
     .   : milestone, 865,
    master - mean (888ms)  : 850, 926
     .   : milestone, 888,

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