chore: import upstream snapshot with attribution

tests/unit/compression/eval-cost-meter.test.ts

@@ -0,0 +1,34 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { createCostMeter } from "../../../open-sse/services/compression/eval/costMeter.ts";
+
+describe("eval cost meter", () => {
+  it("accumulates spend and reports it", () => {
+    const m = createCostMeter(1.0);
+    m.add(0.2);
+    m.add(0.3);
+    assert.equal(Math.round(m.spent * 100) / 100, 0.5);
+    assert.equal(m.exceeded, false);
+  });
+
+  it("wouldExceed is true when the next charge crosses the cap", () => {
+    const m = createCostMeter(1.0);
+    m.add(0.8);
+    assert.equal(m.wouldExceed(0.3), true);
+    assert.equal(m.wouldExceed(0.1), false);
+  });
+
+  it("marks exceeded once spend crosses the cap", () => {
+    const m = createCostMeter(1.0);
+    m.add(0.9);
+    m.add(0.2);
+    assert.equal(m.exceeded, true);
+  });
+
+  it("a cap of 0 or undefined means unbounded (never exceeds)", () => {
+    const m = createCostMeter(0);
+    m.add(1000);
+    assert.equal(m.wouldExceed(1000), false);
+    assert.equal(m.exceeded, false);
+  });
+});