Expected Behavior

A user can apply java agent to the Gradle daemon process, and build with configuration cache enabled.

Current Behavior (optional)

• Attached agent is reported as a configuration cache problem when using TestKit to run the build (see also False positive configuration cache violation running TestKit in IntelliJ #25929), even if the agent does not register instrumentation.
• Legacy instrumentation mode exposes instrumented bytecode to third-party agents (which is problematic for e.g. Jacoco's online instrumentation).

Context

TestKit is the primary concern, as plugin authors want to test their plugins with the configuration cache.

FWIW, Jacoco is not fully supported with TestKit yet (see #1465, #16603).

### Tasks
- [ ] https://github.com/gradle/gradle/issues/25929