Greptile Summary

This PR adds OpenCode trace extraction support by reading the x-session-affinity request header when opencode_trace_enabled is set to true, following the same pattern used for Claude Code and Codex tracing.

• Adds OpenCodeTraceEnabled config field to tracing.Config (defaults false) and the corresponding setDefaults entry in conf.go.
• Implements tryExtractTraceIDFromOpenCodeRequest in the trace middleware, inserted between the primary header check and the ClaudeCode check in priority order.
• Adds three integration tests covering: feature-flag disabled, header-sets-trace, and primary-header-takes-precedence scenarios.

Confidence Score: 5/5

Safe to merge; the new extractor is gated behind a feature flag that defaults to false, so existing deployments are unaffected.

The change is additive and opt-in. The extractor follows the same shape as the Codex extractor, is well-tested, and the feature flag defaults to false so no existing behavior changes on upgrade.

internal/server/middleware/trace.go — the extractor is missing whitespace trimming (noted in prior review threads) and has no trace-ID format validation, unlike the ClaudeCode path.

Important Files Changed

Sequence Diagram

sequenceDiagram
    participant Client as OpenCode Client
    participant MW as WithTrace Middleware
    participant Ext as tryExtractTraceIDFromOpenCodeRequest
    participant DB as TraceService

    Client->>MW: POST /v1/chat/completions x-session-affinity: session-id
    MW->>MW: getTraceIDFromHeader() → empty
    MW->>Ext: "config.OpenCodeTraceEnabled == true"
    Ext->>Ext: c.GetHeader("x-session-affinity")
    Ext-->>MW: "traceID = session-id"
    MW->>DB: GetOrCreateTrace(projectID, traceID)
    DB-->>MW: trace entity
    MW->>MW: contexts.WithTrace(ctx, trace)
    MW->>MW: shared.WithSessionID(ctx, traceID)
    MW-->>Client: continue to handler

_{Reviews (2): Last reviewed commit: "feat: opencode trace, close #1740" | Re-trigger Greptile}