[bug] 0.221.0+ tracing panic: Function log expected to be present (no FunctionStart event?)

[artenc]

Product

BAML

Describe the bug

Summary

After upgrading @boundaryml/baml from 0.220.0 to 0.221.0, our application crashes with a tracing/storage panic originating from the BAML runtime.

The issue persists in 0.222.0.

Downgrading back to 0.220.0 resolves the problem completely.

Error

thread '<unnamed>' (128394) panicked at baml-runtime/src/tracingv2/storage/storage.rs:546:22:
Function log expected to be present (no FunctionStart event?). Did you forget to track_function()?
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5, aborting
Aborted (core dumped)

Versions tested

• ✅ @boundaryml/baml@0.220.0 — works
• ❌ @boundaryml/baml@0.221.0 — crashes
• ❌ @boundaryml/baml@0.222.0 — crashes

Expected behavior

BAML function calls should execute normally without runtime panics, and tracing/collector logs should be handled safely.

Actual behavior

The process aborts due to a Rust panic in:

baml-runtime/src/tracingv2/storage/storage.rs:546:22

The error indicates that a FunctionLog is being accessed without a corresponding FunctionStart event:

Function log expected to be present (no FunctionStart event?)

Additional context

• We are using Collector / tracing functionality.
• The issue appears to be a regression introduced in 0.221.0.
• Likely related to tracing v2 lifecycle or event ordering/cleanup.

Environment

• Node.js: v22.15.0
• OS: Ubuntu 24.04.4 LTS
• Package manager: npm 10.9.2
• BAML package: @boundaryml/baml

Notes / Hypothesis

This may be caused by:

• Missing or dropped FunctionStart events in tracing v2
• Collector lifecycle or reference-counting issue
• Race condition or cleanup happening before logs are accessed

Please let me know if you'd like additional debug output (RUST_BACKTRACE=1, BAML_LOG=debug) or a minimal repro.

Reproduction Steps

Consistently reproducible after upgrading from 0.220.0 → 0.221.0+.

If needed, I can attempt to provide a minimal reproduction case.

BAML Version

No response

Language/Framework

None

LLM Provider

None

LLM Model

No response

Operating System

None

Browser

None

Code Editor

None

[linear]

BAML-600