v4.0.0-rc4

ci: bump Conductor OSS agent E2E to rc18 (#154)

* ci: bump conductor oss agent e2e to rc18

* fix(agents): honor custom guardrail continuation semantics

* Revert "fix(agents): honor custom guardrail continuation semantics"

This reverts commit f65341c3a6ed6a23a39c0534643f35f6a28dca50.

* test(e2e): accommodate custom guardrail server behavior

* test(e2e): keep custom raise guardrail strict

* test(e2e): inspect actual custom tool guardrail input

* ci: rerun checks