APC Spec Rule: Unknown .apc/ Files Must Not Be Treated as Agent Instructions

The APC folder structure specification requires that consumers ignore any .apc/ paths not formally defined by APC or an approved extension, preventing unrecognised files from being silently treated as agent instructions. This rule matters because different tools handle unknown files differently — one may ignore them while another feeds every Markdown file in the directory to its agent, causing inconsistent behaviour across the same codebase. A file's location inside .apc/ alone does not grant it semantic authority; a consumer must be able to identify what a path means before acting on it. Teams wanting to make instructions universally applicable should place them in AGENTS.md, or use defined paths such as .apc/rules/ or .apc/skills/ for scoped rules and callable procedures. Sensitive data like credentials or runtime caches should never be stored in .apc/, as the unknown-path ignore rule is a parsing convention, not a privacy safeguard.