Matrix API

ToolCase names one tool invocation and its arguments. ServerCase groups tool cases under the server that owns them. ToolMatrix validates and expands those cases without starting processes or network work.

ToolMatrix.cases() returns ToolMatrixCase values for scripts. ToolMatrix.parametrize() produces normal pytest parametrization with stable case IDs and marks. Work starts only when the selected case is executed.

Matrices directly invoke known tools. They do not test which tool an agent chooses. HarnessMatrix combines harnesses, servers, tools, and trials for agent cases; its HarnessMatrixCase.run() method executes one expanded case. Keep deterministic tool contracts in ToolMatrix.