# MessageWindowChatMemory, maxMessages = 4 and 5

maxMessages = 4. One system message, then one user+assistant turn at a time:
  after turn 1: S:SYS-1 | U:u1 | A:a1
  after turn 2: S:SYS-1 | U:u2 | A:a2
  after turn 3: S:SYS-1 | U:u3 | A:a3
  after turn 4: S:SYS-1 | U:u4 | A:a4

A second, different system message arrives:
  after SYS-2:  U:u4 | A:a4 | S:SYS-2

maxMessages = 5 (odd), no system message:
  after turn 1: U:u1 | A:a1
  after turn 2: U:u1 | A:a1 | U:u2 | A:a2
  after turn 3: U:u2 | A:a2 | U:u3 | A:a3
  after turn 4: U:u3 | A:a3 | U:u4 | A:a4