Compiler context describes the declarations available at a generated body's location. The tool-server fixture gives the compiler a real class and method request:
__llm__ void Account::deposit(int amount) { Add amount to cents. }
Here amount is a parameter and cents is private class state. The agent can ask get_task for the target interface and get_context for the enclosing scope, then use lookup or member inspection to check names.
Because the body belongs to Account, it can access cents. The free function peek(Account&) in the same fixture cannot. Compiler context makes that difference visible without sending the entire raw file to the model. Candidate compilation checks the proposed use of those declarations.
Source: 06_tools.cpp.