Agent Operations
Canary
Also: canary value, canary token
A fake secret or marker planted on purpose, so that any appearance of it reveals unwanted reading or leaking.
In more detail
A canary is an invented value that opens nothing, such as a made-up API key in a test fixture. If it later shows up in network traffic, a log or an agent's final answer, you know the data was read and moved. Evaluations use fresh canaries per trial so results are not contaminated.