Add tool ranker fallback policy tests

src/ai/tool-ranker-fallback.ts

@@ -0,0 +1,23 @@
+import {ToolRankerFallbackPolicy} from "../common/policies.js";
+
+export type ToolRankerFallbackSelection = {
+    toolNames: string[];
+    usedRanker: boolean;
+};
+
+export function resolveToolRankerFallbackSelection(params: {
+    fallbackPolicy: ToolRankerFallbackPolicy;
+    availableToolNames: readonly string[];
+}): ToolRankerFallbackSelection {
+    if (params.fallbackPolicy === ToolRankerFallbackPolicy.NO_TOOLS) {
+        return {
+            toolNames: [],
+            usedRanker: false,
+        };
+    }
+
+    return {
+        toolNames: [...params.availableToolNames],
+        usedRanker: false,
+    };
+}