Fix Muzzle classloader reuse across projects

[bric3]

What Does This Do

Cache Muzzle's bootstrap/tooling classloader pairs by both ordered classpaths. Create each pair atomically for concurrent checks, reuse it within the build, and replace the cache when the build changes.

Add a GraalVM/OpenTelemetry regression reproducer and MuzzleAction coverage for classpath changes, isolation, build invalidation and concurrent lookups.

Motivation

When graal-native-image-20.0 ran before opentelemetry-1.47 in the same worker, OpenTelemetry could reuse GraalVM's loaders and fail with NoClassDefFoundError: OtelInstrument despite declaring otel-bootstrap. The previous cache compared only the combined classpath file count and could also expose undeclared bootstrap classes.

This was spotted in #12848

Additional Notes

The cache retains one pair per distinct bootstrap/tooling classpath instead of a single pair. Real GraalVM/OpenTelemetry version checks and memory measurements have not been run.

Contributor Checklist

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-14T17:05:02.280183Z	989d1c5	Draft marked ready
🔒 Security Review	✅ Completed 2026-10-14T17:06:19.470174Z	989d1c5	Draft marked ready

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[datadog-official]

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 59.55% (-0.02%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 989d1c5 | Docs | Give us feedback!}

[datadog-official]

More details

Static review supports that loader pairs are isolated by both ordered classpaths, created atomically, and invalidated when the build timestamp changes. Runtime behavior remains unverified.

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[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	13.93 s	13.84 s	[-0.1%; +1.3%] (no difference)
startup:insecure-bank:tracing:Agent	12.87 s	12.92 s	[-1.2%; +0.4%] (no difference)
startup:petclinic:appsec:Agent	17.02 s	16.83 s	[+0.2%; +2.0%] (maybe worse)
startup:petclinic:iast:Agent	16.89 s	17.11 s	[-2.4%; -0.2%] (maybe better)
startup:petclinic:profiling:Agent	16.52 s	16.63 s	[-1.7%; +0.4%] (no difference)
startup:petclinic:sca:Agent	17.15 s	16.87 s	[+0.7%; +2.6%] (maybe worse)
startup:petclinic:tracing:Agent	16.06 s	16.24 s	[-1.8%; -0.4%] (maybe better)

Commit: 989d1c5b · CI Pipeline · Benchmarking Platform UI

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Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.