Secondary source

A secondary source is a description of something rather than the something itself. A handoff artifact, a compaction summary, a comment on a ticket, your own explanation of how the code works, or the agent's recollection from earlier in the session all count. Each one was accurate at some moment, through someone's eyes, at some level of detail. None of them is the code.

The problem is not that secondary sources are wrong, it is that they are quietly incomplete. A summary keeps what seemed important when it was written. If the task changes, the missing detail is often exactly what you now need, and nothing in the summary signals that it was dropped. Agents treat a clean summary with the same confidence as a file they just read, so the error stays invisible until something breaks.

Use secondary sources for orientation and primary sources for decisions. A handoff note is a good map of where to look; it is a poor substitute for looking. Before the agent changes code based on a summary, have it open the files the summary describes. When you write a handoff yourself, include paths and commands so the next reader can go straight to the source.