Clean up TODOs in the new subsystem.

Note that the TODOs about turning exceptions into logs no longer apply
because we are not in Mainline and can be more aggressive for
correctness.

This leaves us with 2 STOPSHIP TODOs.

Bug: 263504888
Test: presubmit
Change-Id: I20c3a24d14d475d33aa85a478b7a80a128f739cb