Azure Functions Java: Duplicate log entries in Portal Log Stream since agent 3.7.0

PR #3962 における agent 3.7.0 の依存関係の変更を確認し、OpenTelemetry Instrumentation 2.9.0 と 2.10.0 を比較します。JUL の処理と Portal Log Stream のパスに重点を置いてください。APPLICATIONINSIGHTS_ENABLE_AGENT=true と context.getLogger().info() を使用して再現し、その後 agent 3.6.2 での動作と比較します。完了の条件は、Portal Log Stream に [undefined] の重複がなく、ログが App Insights のトレースに 1 回だけ表示されることです。

Description

When APPLICATIONINSIGHTS_ENABLE_AGENT=true (the default), calls to context.getLogger().info() produce duplicate entries in the Azure Portal Log Stream:

• [Information] from the host RPC log pipeline
• [undefined] from the AI agent's JUL auto-instrumentation

The duplication only appears in the Portal Log Stream. In the App Insights traces table, the user log message appears once (from the agent only). The entries stored in App Insights are identical in structure between the working and broken agent versions.

Regression

Introduced in agent 3.7.0, which upgraded OpenTelemetry Java Instrumentation from 2.9.0 to 2.10.0 (PR #3962). No AI agent code changes were made between 3.6.2 and 3.7.0 regarding JUL handling. The behavioral change comes from the upstream OTel dependency bump.

With 3.6.2, the agent captures JUL logs and sends them to App Insights without producing a duplicate in the log stream. Starting with 3.7.0, the same capture also produces an [undefined] entry in the log stream.

Affects all Java versions (8, 11, 17, 21, 25) on Linux Dedicated.

Workarounds

No workaround fully restores the 3.6.2 behavior (user logs in AI traces without log stream duplication).

Expected behavior

The agent should capture JUL logs for App Insights without producing a duplicate [undefined] entry in the log stream, as it did in 3.6.2.