## Summary
Large error stacks and messages can OOM the worker process when
serialized into OTel spans or `TaskRunError` objects. This was reported
when throwing an error with a massive `.stack` property from a chat
agent hook.
This adds frame-based stack truncation (similar to Sentry's approach)
plus message length limits, applied consistently across all error
serialization paths.
### What changed
**`packages/core/src/v3/errors.ts`**
- `truncateStack()` — parses `error.stack` into message lines + frame
lines, caps at 50 frames (keep top 5 closest to throw + bottom 45 entry
points, with "... N frames omitted ..." in between). Individual lines
capped at 1024 chars.
- `truncateMessage()` — caps error messages at 1000 chars
- Applied in `parseError()` and `sanitizeError()`
**`packages/core/src/v3/otel/utils.ts`**
- `sanitizeSpanError()` now uses `truncateStack` and `truncateMessage`
from `errors.ts` instead of duplicating truncation logic
- Non-Error values (strings, JSON) capped at 5000 chars
**`packages/core/src/v3/tracer.ts`**
- `startActiveSpan` catch block now delegates to `recordSpanException()`
instead of calling `span.recordException()` directly
### Limits
| What | Limit | Rationale |
|------|-------|-----------|
| Stack frames | 50 | Matches Sentry's `STACKTRACE_FRAME_LIMIT` |
| Top frames kept | 5 | Closest to throw site |
| Bottom frames kept | 45 | Entry points / framework frames |
| Per-line length | 1024 | Matches Sentry, prevents regex DoS |
| Message length | 1000 | Bounded but generous |
| Generic string (non-Error) | 5000 | Fallback for JSON/string errors in
spans |
## Test plan
- [x] 17 unit tests in `packages/core/test/errors.test.ts`
- [x] E2E: threw a 300-frame / 5000-char-message error in the ai-chat
reference app, verified truncated stack and message in span via
`get_span_details`
- [x] Verified the run survived the error (no OOM, continued waiting for
next message)
Eric Allam