azure-monitor-opentelemetry-exporter: drops input attributes when sampling-percentage reaches 100% - causes corrupt telemetry

[josteink]

• Package Name: azure-monitor-opentelemetry-exporter
• Package Version: v1.0.0b48
• Operating System: Not relevant
• Python Version: 3.14

Describe the bug
When using azure-monitor-opentelemetry-exporter to export telemetry, and especially when instrumenting HTTP dependencies with httpx, together with sampling, one will encounter that some of the telemetry ends up without any attributes all, marking them in App Insights/Azure Monitor as HTTP POST N/A, HTTP GET N/A, etc.

To Reproduce

Setup Azure Monitor using the default configure_azure_monitor() without any arguments, leaving the default at RateLimitedSampler(5.0).

This triggers a bug in _rate_limited_sampler.py, line 133:

  # current (buggy)
  if sampling_percentage == 100.0:
      new_attributes = {}         # drops all input attributes

Expected behavior
When sampling creates a net set of attributes, it should not throw away the attributes already populated for the span:

  # correct
  if sampling_percentage == 100.0:
      new_attributes = {} if attributes is None else dict(attributes)
      # intentionally no _SAMPLE_RATE_KEY at 100% — that part is correct

Screenshots

Additional context
Especially prevalent with Async python code, but it may not be a requirement to trigger the condition.