feat(FN-4388): complete remaining observability surfaces

Fusion-Task-Id: FN-4388
Fusion-Task-Lineage: 7497a0a1-5edb-4778-b339-118d1fd668f7

scripts/__tests__/cache-stats.test.mjs

@@ -0,0 +1,32 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { collectCacheStats } from "../cache-stats.mjs";
+
+test("collectCacheStats groups role and permanent-agent totals", async () => {
+  const taskStore = {
+    async listTasks() {
+      return [
+        { assignedAgentId: "a1", tokenUsage: { inputTokens: 100, cachedTokens: 50, cacheWriteTokens: 10, outputTokens: 20 } },
+        { assignedAgentId: "a2", tokenUsage: { inputTokens: 200, cachedTokens: 100, cacheWriteTokens: 5, outputTokens: 50 } },
+        { assignedAgentId: "missing", tokenUsage: { inputTokens: 10, cachedTokens: 0, cacheWriteTokens: 0, outputTokens: 2 } },
+      ];
+    },
+  };
+  const agentStore = {
+    async listAgents() {
+      return [
+        { id: "a1", role: "executor", metadata: { type: "permanent" } },
+        { id: "a2", role: "reviewer", metadata: { type: "spawned" } },
+      ];
+    },
+  };
+
+  const result = await collectCacheStats({ taskStore, agentStore });
+
+  assert.equal(result.byRole.find((r) => r.role === "executor")?.total_cached, 50);
+  assert.equal(result.byRole.find((r) => r.role === "reviewer")?.total_input, 200);
+  assert.equal(result.byRole.find((r) => r.role === "unknown")?.total_input, 10);
+  assert.equal(result.byAgent.length, 1);
+  assert.equal(result.byAgent[0].id, "a1");
+  assert.equal(result.byAgent[0].hit_ratio, 50 / 150);
+});