A2AResultReassembler.pushMessage in packages/core/src/agents/a2aUtils.ts checks messageLog[messageLog.length - 1] to avoid pushing duplicate consecutive messages. When messageLog is empty, length - 1 is -1 and array[-1] returns undefined in JavaScript.

While the current behavior happens to work correctly (since undefined !== text evaluates to true, the first message still gets pushed), the code relies on an implicit JavaScript quirk rather than expressing intent clearly. An explicit empty-array guard makes the duplicate check self-documenting and prevents potential issues if the comparison logic changes in the future.

Steps to reproduce

1. Create a new A2AResultReassembler instance
2. Call pushMessage with any text
3. Observe that messageLog[-1] is accessed (returns undefined)

Expected behavior

An explicit length check should guard the last-element access.

Actual behavior

array[-1] is accessed, which returns undefined — works by coincidence, not by design.