feat(FN-4199): complete Step 1 — add capacity helper and settings

Fusion-Task-Id: FN-4199
Fusion-Task-Lineage: fd530f3d-ef2e-4684-ab05-5aaab6856f15

packages/core/src/__tests__/capacity.test.ts

@@ -0,0 +1,55 @@
+import { describe, expect, it } from "vitest";
+import { computeCapacityRisk } from "../capacity.js";
+
+describe("computeCapacityRisk", () => {
+  it("is at risk when todo exceeds threshold and idle non-ephemeral count is zero", () => {
+    expect(
+      computeCapacityRisk({
+        todoCount: 21,
+        inProgressCount: 3,
+        inReviewCount: 1,
+        idleNonEphemeralAgentCount: 0,
+        threshold: 20,
+      }),
+    ).toMatchObject({
+      atRisk: true,
+      reason: "todo-exceeds-threshold-and-no-idle-agents",
+    });
+  });
+
+  it("is not at risk when idle non-ephemeral agents are available", () => {
+    expect(
+      computeCapacityRisk({
+        todoCount: 30,
+        inProgressCount: 2,
+        inReviewCount: 4,
+        idleNonEphemeralAgentCount: 1,
+        threshold: 20,
+      }),
+    ).toMatchObject({ atRisk: false, reason: "ok" });
+  });
+
+  it("is not at risk when todo equals threshold", () => {
+    expect(
+      computeCapacityRisk({
+        todoCount: 20,
+        inProgressCount: 0,
+        inReviewCount: 0,
+        idleNonEphemeralAgentCount: 0,
+        threshold: 20,
+      }),
+    ).toMatchObject({ atRisk: false, reason: "ok" });
+  });
+
+  it("is not at risk when todo is below threshold with zero idle agents", () => {
+    expect(
+      computeCapacityRisk({
+        todoCount: 19,
+        inProgressCount: 1,
+        inReviewCount: 1,
+        idleNonEphemeralAgentCount: 0,
+        threshold: 20,
+      }),
+    ).toMatchObject({ atRisk: false, reason: "ok" });
+  });
+});