test: reduce sidecar testing flakes

[morrisonlevi]

Description

This fixes two different sidecar flakes.

1. inWebServer() retries the entire server lifecycle when no traces are received, but testComposerInteroperabilityWhenNoInitHook expects no traces. It then kills a healthy PHP server and immediately restarts it on the same port. With telemetry enabled, the extension can start a sidecar that briefly outlives the forcibly stopped PHP process and may retain the server socket. The unnecessary retry then fails with Server never came up. Fixed by setting retries=0 for this test. There are no other tests I could find that also assert that no traces are made.
2. Fixes a race in the agent_sampling_sidecar.phpt caused by matching stale shared-memory data from earlier or parallel test processes. Each invocation now uses unique sampling configuration markers, ensuring
   it waits for its own sidecar updates. Failures also report concise, actionable messages instead of dumping large shared-memory buffers.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[datadog-datadog-us1-prod]

 

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DataDog/apm-reliability/dd-trace-php | test_extension_ci: [8.4] — 🔧 Needs a code fix, caused by this PR

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ℹ️ Info

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🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 55.03% (+0.00%)

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[bwoebi]

Is there a specific reason you dropped the debuggability of this test? Otherwise probably fine.

[morrisonlevi]

I guess you consider hexdumps more debuggable than messages? xD
I can revert that aspect, sure.

[bwoebi]

Why not both :-P

[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 2026-09-11T23:55:21.866683Z	b92e6bc	Draft marked ready
🔒 Security Review	✅ Completed 2026-09-11T23:56:27.145135Z	b92e6bc	Draft marked ready

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