BoundaryML/baml · error · io::Error

WASM history boundary {} was not found

Error message

WASM history boundary {} was not found

What it means

The open method of the WASM history store resolves a BoundaryId to a stored run; if the id is not present in the boundaries map it returns io::Error NotFound 'WASM history boundary ... was not found'. Unlike the 'not begun' errors, open() only reads, so this means no such boundary exists at all (never created in this instance, or already evicted).

Source

Thrown at baml_language/crates/bridge_wasm/src/runs.rs:190

        boundary.value_writer.flush()?;
        Ok(())
    }

    fn list(&self, filter: &RunFilter) -> Vec<RunSummary> {
        let mut summaries = self
            .boundaries
            .keys()
            .filter_map(|boundary_id| self.open(*boundary_id).ok())
            .filter(|run| history_run_matches_filter(run, filter))
            .map(|run| summarize_history_run(&run))
            .collect::<Vec<_>>();
        summaries.sort_by_key(|summary| std::cmp::Reverse(summary.created_at_ms));
        summaries
    }

    fn open(&self, boundary_id: BoundaryId) -> io::Result<bex_events::run::Run> {
        let boundary = self.boundaries.get(&boundary_id).ok_or_else(|| {
            io::Error::new(
                io::ErrorKind::NotFound,
                format!(
                    "WASM history boundary {} was not found",
                    boundary_id.to_wire_string()
                ),
            )
        })?;
        let value_segments = boundary.value_segments();
        open_boundary_from_value_segments(&value_segments)
    }

    fn read_value(
        &self,
        boundary_id: BoundaryId,
        value_ref_id: &str,
    ) -> io::Result<HistoryValueReadResult> {
        let Some(boundary) = self.boundaries.get(&boundary_id) else {
            return Ok(HistoryValueReadResult::Missing);

View on GitHub (pinned to bd85ce9dee)

Solutions

  1. Re-register or re-begin the boundary in the current WASM instance before opening it
  2. Validate boundary ids against boundaries.list()/summaries before calling open
  3. Treat NotFound as 'history unavailable in this session' in the UI instead of failing hard
  4. Do not persist BoundaryId wire strings across reloads as valid handles

Example fix

// before
const run = runs.open(idFromStorage);
// after
const known = runs.list_summaries().some(s => s.id === idFromStorage);
const run = known ? runs.open(idFromStorage) : null;
Defensive patterns

Strategy: try-catch

Validate before calling

function boundaryExists(runs, id) {
  return runs.list_summaries().some(s => s.id === id);
}

Try / catch

try {
  const run = runs.open(boundaryId);
} catch (e) {
  if (String(e.message).includes('was not found')) {
    run = null; // history unavailable in this session
  } else throw e;
}

Prevention

When it happens

Trigger: Calling open with a BoundaryId from a previous session/reload, a typo'd wire string, or after the boundary was removed; also invoked by list paths that iterate stale ids.

Common situations: Page reloads in the browser lose in-memory WASM state while persisted boundary ids remain in history listings; replay code (warm_history...) referencing ids not re-registered in the new instance.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/b4ca603cf367721b. Report an issue: GitHub.