feat(eve): add braintrustEveProvider for eve's instrumentation bridge

[Chad Hietala (chadhietala)]

Summary

Add a new Braintrust instrumentation provider (braintrustEveProvider) that consumes eve's lifecycle event bus — the instrumentation bridge proposed in vercel/eve#1799 and landed in eve ≥ 0.34.0.

Instead of parsing stream events manually (the legacy braintrustEveHook + braintrustEveInstrumentation path), the provider receives structured lifecycle events directly from eve's bus:

• session.started/completed/failed → session metadata + span cleanup
• turn.started/completed/failed → eve.turn TASK spans with subagent parent lineage
• step.attempt.started/completed/failed → eve.step LLM spans
• model.call.started/completed/failed → input/output/usage logged to the step span
• action.started/completed/failed → TOOL spans for tools, subagents, remote agents

The provider uses eve's replay-stable idempotency keys for deterministic span IDs and ctx.state for durable per-operation state — replacing the old defineState + manual LLM-input capture machinery.

Content redaction

recordInputs and recordOutputs default to false (metadata only). When both are false, the provider declares capture: "metadata" so eve never builds the content projection at all. When either is true, the provider declares capture: "content" and guards each field independently in its handlers. This mirrors eve's per-destination ContentOptions model (agentRuns vs localTraces).

Usage

Enable the instrumentation providers layout in your agent config, then export the Braintrust provider from agent/instrumentation/braintrust.ts:

// agent/agent.ts
import { defineAgent } from "eve";

export default defineAgent({
  experimental: { instrumentationProviders: true },
  // ...model, tools, etc.
});

// agent/instrumentation/braintrust.ts
import { braintrustEveInstrumentation } from "braintrust";
import { defineInstrumentation } from "eve/instrumentation";

export default defineInstrumentation(
  braintrustEveInstrumentation({
    recordInputs: true,
    recordOutputs: true,
  }),
);

No defineState, no setup, no initLogger, no hook file — the provider initializes the Braintrust logger from BRAINTRUST_API_KEY by default. Pass setup only to override:

braintrustEveInstrumentation({
  recordInputs: true,
  recordOutputs: true,
  setup: ({ agentName }) => {
    initLogger({ projectName: agentName, apiKey: process.env.BRAINTRUST_API_KEY });
  },
})

On eve ≥ 0.34.0 with experimental.instrumentationProviders enabled, the provider handles everything — the legacy braintrustEveHook is a no-op. On older eve (or without the flag), both the hook and instrumentation work as before. The version branching is internal — the user never sees it.

Files

• js/src/vendor-sdk-types/eve-provider.ts — vendored lifecycle event types
• js/src/instrumentation/plugins/eve-provider.ts — provider implementation
• js/src/instrumentation/plugins/eve-plugin.ts — version detection + let binding, default setup that calls initLogger from BRAINTRUST_API_KEY
• js/src/exports.ts / js/src/instrumentation/index.ts — export wiring
• e2e/scenarios/eve-instrumentation/agent/agent.ts — enables experimental.instrumentationProviders
• e2e/scenarios/eve-instrumentation/agent/instrumentation.ts — uses the new clean API

Test plan

• tsc --noEmit passes
• Existing eve-plugin.test.ts (23 tests) passes
• E2E scenario against eve ≥ 0.34.0 with provider path
• E2E scenario against eve < 0.34.0 with legacy path (no regression)

[Luca Forstner (lforst)]

Thanks! I think I am gonna give it a shot myself.