Add http.endpoint tag

[y9v]

What does this PR do?
This PR adds http.endpoint tag for requests for all rack applications (nested and standalone).

Motivation:
We want to be able to infer routes for rack applications for which we can't get the exact route. This new http.endpoint tag will use http.route tag value whenever it is available, and will infer the route from the request path when the route is not available.

Change log entry
Yes. Tracing: Add http.endpoint tag which contains the route whenever the routing information is available, and falls back to route inferred from the request path.

Additional Notes:
APPSEC-58489

How to test the change?
CI and manual testing

[github-actions]

Typing analysis

Ignored files

This PR introduces 1 ignored file. It decreases the percentage of typed files from 35.91% to 35.87% (-0.04%).

Ignored files (+1-0)

❌ Introduced:

lib/datadog/tracing/contrib/rack/route_from_path_inference.rb

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-10-27 14:05:57

Comparing candidate commit d43e6b4 in PR branch add-http-endpoint-tag-when-route-is-missing with baseline commit 05d35a2 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 44 metrics, 2 unstable metrics.

[datadog-datadog-prod-us1]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 99.07%
• Total Coverage: 98.43% (-0.15%)

View detailed report

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[Strech]

LGTM, I think there are some discrepancy between code and typespec. I've left few suggestions for route inferring, but nothing blocking. Well done!

[vpellan]

LGTM! (Comments are non-blockers)