Stop the browser tracing its own trace-export requests

[hahn-kev-bot]

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🤖 AI summary

The bug

When opening LexBox, the browser traced its own OTel trace-export requests. The exporter POSTs trace batches to /v1/traces; that request became a span, which got exported, producing another export request → a feedback loop that grew unbounded.

Root cause

The dependency bump in #2544 took @opentelemetry/otlp-exporter-base from 0.208 → 0.221, which removed the browser sendBeacon and XHR transports and now sends all exports via fetch. Previously the exporter used the untraced sendBeacon transport, so exports were a blind spot; now they go through fetch, which our tracing wraps.

The OTLP fetch-transport does try to avoid this loop — it sends via globalThis.fetch.__original when present, to bypass any fetch wrapper. But that escape hatch never survives in our setup: ZoneContextManager pulls in zone.js, which re-wraps window.fetch after app.html runs, and the zone wrapper (the fetch the exporter actually reads) carries no __original. So the export flows through our whole proxy chain and hits both span-creating layers: @opentelemetry/instrumentation-fetch and our own traceFetch in hooks.client.ts.

Fix

Zone's wrapper creates no span; only traceFetch and instrumentation-fetch do. So make both skip the collector URL, sharing one pattern (TRACE_EXPORT_URL_PATTERN). No export span is created regardless of how fetch is wrapped — no dependence on the __original convention or on wrap ordering.

• frontend/src/lib/otel/otel.shared.ts — add TRACE_EXPORT_URL_PATTERN and an early return fetch() in traceFetch for that URL (no span).
• frontend/src/lib/otel/otel.client.ts — ignoreUrls: [TRACE_EXPORT_URL_PATTERN] on instrumentation-fetch and instrumentation-xml-http-request.
• otel/collector-config.yaml — a filter/drop-trace-export processor drops any span targeting /v1/traces as an ops-level safety net (also deployable on its own as an immediate hotfix, and covers older/cached clients).

Verified

Ran against a live build: a burst of app fetches drained into a couple of batch exports, then /v1/traces requests flatlined during idle (the old loop climbed ~1/sec indefinitely). Normal app requests are still traced; only the collector POSTs are skipped. No new console errors.

Follow-up (not in this PR)

The custom OTLPTraceExporterBrowserWithXhrRetry wrapper is now largely dead weight (its beacon-retry path is unreachable once all transports resolve to fetch). Handed off as a separate cleanup task.

Test plan

• Burst of app fetches → /v1/traces requests flatline during idle (no runaway growth).
• Normal app fetch/XHR requests are still traced.
• Verify traces still arrive in Honeycomb.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: a18d6ea5-7117-402b-bb37-2e2fd419c140

📥 Commits

Reviewing files that changed from the base of the PR and between c8116c5 and e0c23d4.

📒 Files selected for processing (2)

• frontend/src/app.html
• otel/collector-config.yaml

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

The browser now preserves the native fetch reference for OpenTelemetry export requests. The collector drops spans for /v1/traces requests and runs this filter in the traces pipeline.

Changes

Trace loop prevention

Layer / File(s)	Summary
Native fetch escape hatch frontend/src/app.html	The inline script stores the native fetch reference in window.fetch.__original for OpenTelemetry OTLP export requests.
Collector export filtering otel/collector-config.yaml	The collector drops export-request spans that match /v1/traces in http.url or url.full. The traces pipeline runs this filter before later processors.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to e0c23

This PR prevents trace-export requests from generating additional tracing spans and adds a collector safety filter; no actionable merge-blocking risk remains beyond normal checks and review.

Poem

A rabbit found a fetch by moonlit light

It kept the native path in sight
The traces hopped, then stopped their loop
The collector sorted every group
“Clean exports!” cheered the rabbit bright

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing browser tracing of its own trace-export requests.
Description check	✅ Passed	The description directly explains the runaway trace-export loop, its cause, the proposed fixes, and the test plan. It is related to the changeset.

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (2 skipped: 2 unsupported.)

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/otel-trace-loop-lexbox-9c7178

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[rmunn]

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