fix(observability): the renderer trace proxy stops tracing itself

[t3dotgg]

The renderer sends its spans to the server through the trace proxy (POST /api/observability/v1/traces), up to once a second while it has spans buffered. Each of those POSTs made about 4 server spans of its own: the HTTP server span, auth, session verify, and a SQL query. When an upstream collector is set, the forward added an HTTP client span too. Renderers make about 2.3 spans a second, so the proxy wrote more server spans than it forwarded, for as long as a window stayed open.

Two smaller gaps in the same path: renderer attributes skipped the truncation that server spans get, and a decode failure logged the whole OTLP body.

Fix

• The proxy handler runs with Effect.withTracerEnabled(false). This drops the auth, session, SQL, and forward spans.
• A new untracedRequestsLayer in http.ts sets HttpMiddleware.TracerDisabledWhen for the proxy path. This drops the HTTP server span, which starts before routing. It compares the path without the query string, so ?x=1 does not bring the span back.
• TracerDisabledWhen is one value for the whole server, and the last layer to provide it wins. So makeRoutesLayer provides untracedRequestsLayer last, and the comment says to add paths to its list instead of providing the value again. The server test fails if a later layer replaces it.
• Decoded renderer attributes go through truncateTraceAttributes, like server spans.
• The decode failure warning no longer includes the request body.

Tradeoffs

• The proxy route makes no server spans. A failed forward to the collector, a decode failure, and a rejected session credential still log a warning. A request with no credential or without the needed scope gets its 401 or 403 with no span and no log, and the error's traceId is unavailable.
• Renderer attribute strings over 500 characters, including strings nested in arrays and objects, are cut in the local trace file, the same as server spans. The OTLP body forwarded to an upstream collector is unchanged.

Verified

• Server test: posts a renderer export to the plain path and to the path with ?x=1, with an upstream collector set. It checks both exports are forwarded and the server records zero spans. Then it sends a GET to /api/auth/session and checks that it still makes an http.server GET span.
• Mutation checks, each one fails the server test: no withTracerEnabled(false) (auth, session, SQL, and http.client POST spans), no untracedRequestsLayer (http.server POST), an exact URL match (http.server POST for the query URL), another layerTracerDisabledForUrls merged after it in makeRoutesLayer (http.server POST), and a predicate that matches every request (no http.server GET).
• Shared test: oversized renderer span and event attributes are clamped. It fails without the truncateTraceAttributes call.
• vp test run on apps/server/src/server.test.ts (203 passed) and packages/shared/src/observability.test.ts (23 passed). Lint, format, and typecheck for t3 and @t3tools/shared.

Made by Claude Opus 5.5 (1M context) in Claude Code, running in T3 Code.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Oversized span and event attributes in trace data are now shortened consistently, keeping exported trace information within supported limits.
  • Browser trace exports are forwarded to the configured collector without adding server-side spans, including when the export request contains a query string.
  • Trace decoding and recording warnings no longer include the full decoded request body.
  • Server-side tracing remains available for other requests, including authentication session requests.

[macroscopeapp]

Approvability

Verdict: Approved at fc4e2dc

Macroscope's review found this PR approvable — This is a narrowly scoped observability fix that stops the trace proxy from generating redundant spans, handles query strings, removes request-body logging from decode warnings, and bounds locally stored renderer attributes. Functional proxy behavior and other-route tracing remain unchanged, with targeted regression tests covering the new behavior.

No code changes detected at 79eef9e. Prior analysis still applies.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.5 KiB	+8 B (+0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	+8 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.4 KiB	0 B (0.0%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.2 KiB	56.2 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	9	9	0 (0.0%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	−28 B (−0.2%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	0 B (0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−28 B (−0.4%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: 92f0af2 · PR result: 79eef9e · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 113.9 KiB
• Claude decoded thread snapshot: 114.7 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

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📝 Walkthrough

Walkthrough

The OTLP trace proxy disables handler and HTTP server tracing for its path, including requests with query strings. Decode errors and warning logs omit request body JSON. OTLP attribute decoding truncates compacted values. Tests cover proxy forwarding and attribute truncation.

Changes

OTLP trace proxy tracing

Layer / File(s)	Summary
Proxy tracing and error context apps/server/src/http.ts, apps/server/src/server.ts, apps/server/src/server.test.ts	The proxy disables handler tracing, and a final route layer disables HTTP server spans for matching paths. Decode errors and warning logs omit request body JSON. Tests cover forwarding with and without a query string and verify that neither request creates server spans, while a session request still creates a server span.

Decoded trace attribute truncation

Layer / File(s)	Summary
Attribute decoding and truncation packages/shared/src/observability.ts, packages/shared/src/observability.test.ts	Attribute decoding truncates compacted values. A decoder test checks that oversized span and event attributes end with …[truncated] after 500 characters.

Priority: ⬇️ Low

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

Change: Bug fix

Suggested reviewers: maria-rcks

Merge Risk: ⚪ Minimal · up to fc4e2

Trace exports avoid generating their own spans while ordinary server tracing remains enabled, and local truncation leaves collector payloads unchanged. No actionable merge blocker was found; the PR appears ready to merge after normal checks.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
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 identifies the primary change: preventing the renderer trace proxy from tracing its own requests.
Description check	✅ Passed	The description clearly explains the problem, implementation, tradeoffs, testing, and verification. It does not use the template headings or checklist, but it provides the required substantive informa…

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Inline comments:
In `@apps/server/src/server.test.ts`:
- Around line 5800-5818: Provide the recording Tracer.Tracer service to the
entire test effect, including the HttpClient.post calls run under
NodeHttpServer.layerTest; it is currently scoped only to buildAppUnderTest. Keep
the span-name assertions observing the same tracer so restored server spans,
including for the query-string request, are detected.

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