fix(evidence): stabilize real Pi authoring

harness/.pi/extensions/tht-evidence-json-mode.ts

@@ -0,0 +1,14 @@
+import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
+
+export default function (pi: ExtensionAPI) {
+	pi.on("before_provider_request", (event) => {
+		if (typeof event.payload !== "object" || event.payload === null) {
+			return undefined;
+		}
+		return {
+			...event.payload,
+			temperature: 0,
+			response_format: { type: "json_object" },
+		};
+	});
+}