Reduce tracing volume for read-heavy paths

[sjmiller609]

Summary

• sample successful root GET traces at 10% by default via OTEL config
• keep sampled-out GET errors visible with a compact fallback HTTP span
• suppress noisy vm info tracing on read-heavy status paths while keeping outer GetVMInfo error visibility

Testing

• go test ./lib/otel ./lib/hypervisor ./lib/vmm ./cmd/api/config
• go test ./lib/hypervisor/firecracker -run TestNonexistent -count=0
• GOOS=darwin GOARCH=arm64 go test ./lib/hypervisor/vz -run TestNonexistent -count=0
• go test ./cmd/api -run TestNonexistent -count=0

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Note

Medium Risk
Medium risk because it changes OpenTelemetry sampling/span-creation behavior; misconfiguration or overly aggressive suppression could hide useful traces during debugging.

Overview
Reduces tracing volume by introducing configurable sampling for successful server-side HTTP GET requests via otel.successful_get_sample_ratio (default 0.1) and wiring it through config/env, validation, and otel.Init.

Suppresses high-frequency hypervisor HTTP trace spans for read-heavy GET / and GET /api/v1/vm.info calls across Firecracker, VZ, and Cloud Hypervisor clients, while adding an error-only detached hypervisor.get_vm_info span to keep failures visible even when normal GetVMInfo tracing is skipped.

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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Sampler Description produces misleading nested ParentBased output

Low Severity

successfulGETSampler.Description() returns "ParentBased{successful_get_ratio=...}", but the struct is not itself ParentBased — it's used as the root sampler inside sdktrace.ParentBased() in newSuccessfulGETSampler. The SDK's ParentBased builds its own description by embedding the root sampler's Description(), producing a confusing "ParentBased{root:ParentBased{successful_get_ratio=…}, …}" string in diagnostics. The inner description text is inaccurate and could mislead operators into thinking there is double wrapping.

Additional Locations (1)

• lib/otel/http_sampling.go#L16-L22