Cannot reference custom agent capability (system.jdk.jdk-21) as a variable in pipeline script task

[Arumugam_ Prasanth]

I'm using ephemeral agent, there is capability JDK-21.

i've added it in base image 

FROM atlassian/bamboo-agent-base:9.6.8-ubi9

RUN /bamboo-update-capability.sh "system.jdk.jdk21" "/app/jdk-21"

I don't want to add this capability on the template, if added other project also builds looking to build ephemeral agent. this is i'm creating for specific project. 

in the pipeline I trying to call the capability like below one 

JAVA_HOME="${bamboo.capability.system.jdk.jdk-21}"

the above setup where working in static agent not in the ephemeral agent.