Add Claude Code instructions file

[p-datadog]

What does this PR do?

Adds CLAUDE.md with instructions for Claude Code, consolidating rules from existing AGENTS.md and PR #5357 discussions.

Motivation:

Provides Claude Code-specific instructions in the format it reads automatically, separate from Cursor-specific .cursor/rules/ files.

Agent configuration files in this repo:

File	Used by
CLAUDE.md	Claude Code
AGENTS.md	Generic format (some AI tools)
.cursor/rules/*.mdc	Cursor

Note: Claude Code ignores AGENTS.md and only reads CLAUDE.md. This repo's CLAUDE.md references AGENTS.md for project structure and commands to avoid duplication.

Change log entry

None. Internal tooling for AI-assisted development.

Additional Notes:

Consolidates:

• Absolute rules (PR templates, changelog, secrets, versioning)
• GitHub Actions security guidelines (injection prevention, permissions, validation)
• Reference pointers to AGENTS.md and docs/
• Style preferences (StandardRB, trailing commas, RBS)

How to test the change?

Review the file content. No code changes to test.

[datadog-datadog-prod-us1]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 95.11% (+0.00%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 938d040 | Docs | Datadog PR Page | Was this helpful? Give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-02-21 08:15:23

Comparing candidate commit 938d040 in PR branch claude-md-instructions with baseline commit 91be22f in branch master.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 43 metrics, 2 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:profiling - intern mixed existing and new

• 🟩 throughput [+2.419op/s; +2.678op/s] or [+8.068%; +8.932%]

[ivoanjo]

👍 At some point we'll probably want to consolidate these a bit more but ATM let's just experiment and see what works