Custom builds from a release break version synchronization between extension and agent

[pablochacin]

The disruptor is formed by two main components: the extension and the agent that is injected into the targets.

The version of these two components must match to ensure their compatibility. This is controlled when the binaries for a release are built using a constant set at build time that defines the extension version and the corresponding agent version.

However, if when building a custom k6 binary that includes the xk6-disruptor extension variable is not properly set, the resulting extension will use the latest version of the agent regardless of the version of the extension.