Reject invalid refund amounts before automatic action

lib/policy.ts

@@ -50,6 +50,15 @@ export function decide(triage: Triage, payload: InboundPayload): Decision {
 
     case "refund": {
       const amount = triage.refundAmount ?? null;
+      if (amount != null && (!Number.isFinite(amount) || amount <= 0)) {
+        return {
+          status: "escalated",
+          proposedAction: "Confirm a valid refund amount, then approve",
+          actionTaken: null,
+          reason: "refund amount must be finite and greater than zero",
+          draftReply: triage.draftReply,
+        };
+      }
       if (amount != null && amount <= refundAutoLimit) {
         return {
           status: "resolved",

package.json

@@ -7,6 +7,7 @@
     "dev": "next dev",
     "build": "next build",
     "start": "next start",
+    "test": "node --test test/*.test.mjs",
     "lint": "next lint",
     "deploy": "NODE_OPTIONS=--no-deprecation opennextjs-cloudflare build && NODE_OPTIONS=--no-deprecation opennextjs-cloudflare deploy"
   },

test/policy.test.mjs

@@ -0,0 +1,91 @@
+import assert from "node:assert/strict";
+import { readFile } from "node:fs/promises";
+import test, { after } from "node:test";
+import ts from "typescript";
+
+const source = await readFile(
+  new URL("../lib/policy.ts", import.meta.url),
+  "utf8",
+);
+const compiled = ts.transpileModule(source, {
+  compilerOptions: {
+    module: ts.ModuleKind.ESNext,
+    target: ts.ScriptTarget.ES2022,
+  },
+  fileName: "lib/policy.ts",
+  reportDiagnostics: true,
+});
+assert.equal(compiled.diagnostics?.length ?? 0, 0);
+
+const moduleUrl = `data:text/javascript;base64,${Buffer.from(
+  compiled.outputText,
+).toString("base64")}`;
+const { decide } = await import(moduleUrl);
+
+const originalLimit = process.env.REFUND_AUTO_LIMIT;
+process.env.REFUND_AUTO_LIMIT = "50";
+after(() => {
+  if (originalLimit === undefined) delete process.env.REFUND_AUTO_LIMIT;
+  else process.env.REFUND_AUTO_LIMIT = originalLimit;
+});
+
+function refundTriage(refundAmount) {
+  return {
+    category: "refund",
+    urgency: "normal",
+    sentiment: "neutral",
+    refundAmount,
+    draftReply: "We are reviewing your request.",
+    summary: "Refund request",
+  };
+}
+
+const payload = {
+  sender: "customer@example.com",
+  body: "Please refund this order.",
+};
+
+test("auto-resolves valid positive refunds at or below the configured limit", () => {
+  for (const amount of [0.01, 20, 50]) {
+    const decision = decide(refundTriage(amount), payload);
+    assert.equal(decision.status, "resolved", `expected $${amount} to resolve`);
+    assert.match(decision.reason, /<= auto-limit/);
+  }
+});
+
+test("escalates valid refunds above the configured limit", () => {
+  const decision = decide(refundTriage(50.01), payload);
+  assert.equal(decision.status, "escalated");
+  assert.equal(decision.actionTaken, null);
+  assert.equal(decision.reason, "refund $50.01 exceeds auto-limit $50");
+});
+
+test("escalates non-positive and non-finite refund amounts as invalid", () => {
+  const invalidAmounts = [
+    0,
+    -1,
+    Number.NaN,
+    Number.POSITIVE_INFINITY,
+    Number.NEGATIVE_INFINITY,
+  ];
+  for (const amount of invalidAmounts) {
+    const decision = decide(refundTriage(amount), payload);
+    assert.equal(decision.status, "escalated", `expected ${amount} to escalate`);
+    assert.equal(decision.actionTaken, null);
+    assert.equal(
+      decision.proposedAction,
+      "Confirm a valid refund amount, then approve",
+    );
+    assert.equal(
+      decision.reason,
+      "refund amount must be finite and greater than zero",
+    );
+  }
+});
+
+test("preserves the missing-amount escalation", () => {
+  const decision = decide(refundTriage(undefined), payload);
+  assert.equal(decision.status, "escalated");
+  assert.equal(decision.proposedAction, "Confirm refund amount, then approve");
+  assert.equal(decision.reason, "refund amount not stated");
+});