fix(server): RPC spans join the client's trace

[yordis]

• Server RPC spans ignored the trace context the client sends with each request, so every call nested under the long-lived WebSocket connection span instead of the client action that caused it.
• That produced one giant trace per connection, and the web or desktop side of a request never appeared in the same trace as its server work.
• Diagnostics RPCs keep their inner work untraced, and now cost one server span per call.

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Summary by CodeRabbit

• Improvements
  • RPC traces now consistently connect client calls, server processing, and handler work for both unary and streaming requests.
  • Traces include RPC context and aggregate information for unary calls, making request paths clearer in observability tools.

[cursor]

PR Summary

Low Risk
Observability-only change to span parenting and attributes; no auth, data, or RPC behavior changes beyond trace shape.

Overview
RPC server spans now follow the client trace instead of nesting every call under the long-lived WebSocket connection.

The WebSocket RPC server is switched from disableTracing: true to shared rpcServerTracingOptions (ws.rpc prefix, transport/system attributes) so Effect RPC opens one server span per request parented to the client span carried on the wire. The observeRpc* helpers no longer create duplicate ws.rpc.* spans with withSpan; they annotate the RpcServer’s current span (rpc.method, rpc.aggregate, etc.) while metrics and the diagnostics-RPC opt-out stay the same.

Tests now drive a mini RpcClient/RpcServer loop and assert trace linkage: shared trace id, server span parent = client span, handler children parent = server span (unary and streamed).

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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	+16 B (+0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	+7 B (+0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.4 KiB	+9 B (+0.1%)	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	+30 B (+0.2%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	+31 B (+0.5%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	+44 B (+0.1%)	66.4 KiB	✅
Claude	Live turn messages	8	9	+1 (+12.5%)	21	✅

Baseline: 85d6c46 · PR result: d8b1157 · 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: 114.0 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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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository: TrogonStack/t3code/.coderabbit.yaml

Review profile: CHILL

Plan: Advanced

Run ID: f8b04917-a50b-4ccd-9194-f210d9a3d332

📥 Commits

Reviewing files that changed from the base of the PR and between 85d6c46 and d8b1157.

📒 Files selected for processing (3)

• apps/server/src/observability/RpcInstrumentation.test.ts
• apps/server/src/observability/RpcInstrumentation.ts
• apps/server/src/ws.ts

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

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📝 Walkthrough

Walkthrough

The WebSocket RPC server now uses exported tracing options. Trace-enabled unary and streamed RPC methods annotate the current span. Tests check trace propagation and span parentage across client, server, and handler calls.

Changes

WebSocket RPC tracing

Layer / File(s)	Summary
Tracing options and span annotation apps/server/src/observability/RpcInstrumentation.ts	Exports rpcServerTracingOptions with the ws.rpc span prefix and WebSocket/effect-RPC attributes. Trace-enabled unary and stream methods annotate the current span instead of creating method-specific spans. RPC method attributes no longer include the removed default attributes.
Server integration and trace validation apps/server/src/ws.ts, apps/server/src/observability/RpcInstrumentation.test.ts	The WebSocket RPC server uses rpcServerTracingOptions. End-to-end tests check trace IDs, parent spans, RPC attributes, and handler child spans for unary and streamed calls.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant RPCClient
  participant WebSocketRPCServer
  participant RPCHandler
  RPCClient->>WebSocketRPCServer: Invoke unary or streamed RPC
  WebSocketRPCServer->>RPCHandler: Run method with server span
  RPCHandler->>RPCHandler: Create child span

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Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to d8b11

No actionable issue is established, so the change is mergeable after normal checks.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to d8b11

Authenticated clients can now influence the trace identity of server RPC work. Existing authentication and RPC scope checks remain in place, but the limits on trace export and behavior during interrupted or concurrent calls are not established.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — An authenticated WebSocket client can influence the trace identity associated with its server RPC work. The inspected code does not establish effects beyond tracing or determine the exporter’s exposure.

Trust Boundaries and Controls

• observed — Client trace context crosses into server span parentage, while WebSocket authentication and per-method scope checks remain on the inspected request path.

Resilience and Maintainability Implications

• inferred — Per-request span isolation and cleanup on interruption remain unverified because the observed test covers successful sequential calls and the inspected production helpers delegate span lifecycle to RpcServer.

Hardening Proposals

• proposed — Verify how remote sampling flags, baggage, and trace identity affect server export, and check span isolation and termination across concurrent and interrupted requests before relying on these traces for security-sensitive correlation.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: server RPC spans now join the client trace.
Description check	✅ Passed	The description explains the tracing problem and the intended behavior, including the diagnostics RPC behavior. It omits the template headings and checklist, but the core change and rationale are pres…
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 3…
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.

✨ Finishing Touches

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