Is there an escape character in ca65 to add such commands to a text string?
In general: No.
The whole ASCII(Z) mechanic is meant to write device independent code, so adding device specific sequences is rather outside of the scope. To get arbitary inserts, you may want to use the good old .BYTE:
msg .BYTE "Hello ",$05,"World",0
Then again, there is a way ...
CL65 is using "C64" target, while CA65 uses "none".
Adding a -t none should make this disappear.
The CL65 documentation for -t does clearly point out the difference:
-t sys, --target sys
The default for this option is different from the compiler and linker in the case that the option is missing: While the
other tools (...