Terminal sample is busted

[rjrjr]

Launch it, type any character, crash:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: begin 0, end 13, length 12
        at java.base/java.lang.String.checkBoundsBeginEnd(String.java:3319)
        at java.base/java.lang.String.substring(String.java:1874)
        at com.squareup.sample.hellotodo.EditTextWorkflowKt.insertCharAt(EditTextWorkflow.kt:100)
        at com.squareup.sample.hellotodo.EditTextWorkflowKt.access$insertCharAt(EditTextWorkflow.kt:1)
        at com.squareup.sample.hellotodo.EditTextWorkflow$onKeystroke$1.invoke(EditTextWorkflow.kt:72)
        at com.squareup.sample.hellotodo.EditTextWorkflow$onKeystroke$1.invoke(EditTextWorkflow.kt:68)

Arrow keys and return work okay, including return checking / unchecking items in the list.

If you arrow back a bit and type a few chars, they aren't echoed. Instead they act like the right arrow until you reach the end of the line and then you crash as above.