The best verification surface is the session transcript JSONL.
Relevant files for the two C2C sessions:
~/.claude/projects/-home-xertrov-tmp/e2deb862-9bf1-4f9f-92f5-3df93978b8d4.jsonl~/.claude/projects/-home-xertrov-tmp/d5722f5b-6355-4f2f-a712-39e9a113fc06.jsonlUse a unique marker prompt such as:
Reply with exactly: PTY_DELIVERY_20260411_AThen verify:
user message containing the marker appearsThis exact marker was successfully injected into C2C-test-agent2 and produced a normal assistant response.