[codex] Preserve relay trace error causes

[juliusmarminge]

Summary

• preserve sanitized nested cause chains when relay failures are handed to the OTLP tracer
• retain each cause stack in the exported exception stack without changing the public failure value
• add an OTLP integration test covering the outer failure and root cause

Testing

• vp test packages/shared/src/relayTracing.test.ts
• vp check
• vp run typecheck
• vpr typecheck

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Note

Low Risk
Changes are confined to best-effort telemetry sanitization in nonInterferingTracer; application exit/failure behavior is unchanged.

Overview
Relay client tracing now sanitizes failures for OTLP export without changing the failure values the app sees. traceSafeError recursively walks cause chains (with cycle protection), trims Effect-internal frames via cleanTraceStack, and folds nested causes into the exported exception stack as a Caused by: section.

A new integration test builds the real tracing layer with a mocked HTTP client and asserts the ingest payload includes both the outer failure message and the root cause.

^{Reviewed by Cursor Bugbot for commit 56e6585. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Preserve error causes and clean stack traces in traceSafeError

• Expands traceSafeError in relayTracing.ts to propagate nested error causes, using a WeakSet to avoid cycles and appending a Caused by: section to the resulting stack.
• Adds cleanTraceStack helper that strips internal Effect/Generator frames from stack traces.
• Adds tests verifying that exported trace payloads include both the error message and its nested cause.

^{Macroscope summarized 56e6585.}

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/preserve-relay-trace-causes

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[macroscopeapp]

Approvability

Verdict: Approved

This change enhances relay tracing by preserving nested error causes and cleaning up stack traces. The modifications are self-contained to the tracing module, include cycle detection to prevent issues, and only affect debugging output format—not application logic.

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