When killing a background shell process with SIGTERM, if the process doesn't exit within 5 seconds, it's now automatically escalated to SIGKILL. This prevents zombie processes from lingering indefinitely.
Evidence
New SIGKILL escalation timeout in the pty manager (visible in the yM8 structural change adding a 5000ms timeout for SIGTERM→SIGKILL escalation)
Strings lifted out of the shipped bundle, so the claim above can be checked against them.