[Bug]: CBEvent assigns generated uuid to self.id instead of self.id_, so events without an id all share id_=""

Author: manav8826Created Sep 28, 2026Updated Sep 28, 2026

Labelsbugtriage

Bug Description

CBEvent.__post_init__ (llama_index/core/callbacks/schema.py) is meant to generate a uuid when no id is given, but it assigns it to self.id instead of the id_ field:

if not self.id_:
    self.id = str(uuid.uuid4())   # should be self.id_

So every event created without an id keeps id_ == "". LlamaDebugHandler pairs events by id_, so when on_event_start() is called without an event_id, all such events collapse into a single pair.

Version

llama-index-core main (169e450)

Steps to Reproduce

from llama_index.core.callbacks import LlamaDebugHandler, CBEventType

h = LlamaDebugHandler(print_trace_on_end=False)
a = h.on_event_start(CBEventType.LLM)
b = h.on_event_start(CBEventType.LLM)
h.on_event_end(CBEventType.LLM, event_id=a)
h.on_event_end(CBEventType.LLM, event_id=b)

print(repr(a), repr(b))                     # '' ''
print(len(h.get_llm_inputs_outputs()))      # 1 (expected 2)
print(h.get_event_time_info(CBEventType.LLM).total_count)  # 1 (expected 2)

Going through CallbackManager is not affected, since it always passes an explicit id.

Relevant Logs/Tracebacks

bash

`tests/callbacks/test_llama_debug.py::test_get_event_stats` fails consistently on Windows, because two back-to-back `datetime.now()` calls return the same value there, so `total_secs == 0.0`.

### Version

Source: run-llama/llama_index

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