An r3940 vtest failure on freebsd seems to suggest that the child
does not terminate while blocking in a write.

***  v1    debug|Error: Child (74042) Panic at: Mon, 03 Jul 2023 13:40:40 GMT
***  v1    debug|Assert error in CLI_Run(), cache/cache_cli.c line 102:
***  v1    debug|  Condition((VCLI_WriteResult(heritage.cli_out, CLIS_OK, \"Ready\")) == 0) not true.

This might need another iteration.