test: retain mutation failure evidence in trusted CI

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/pr-trusted.yml

@@ -639,7 +639,9 @@ jobs:
 
       - name: Verify accounting coverage and crash recovery
         if: ${{ !cancelled() && matrix.group == 'general-server-without-chat' && matrix.shard_index == 0 }}
-        run: pnpm test:accounting
+        run: |
+          node --test scripts/test-accounting-mutations.test.mjs
+          pnpm test:accounting
 
       - name: Upload accounting coverage
         if: ${{ !cancelled() && matrix.group == 'general-server-without-chat' && matrix.shard_index == 0 }}

scripts/test-accounting-mutations.test.mjs

@@ -0,0 +1,37 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { mkdtemp, mkdir, copyFile, readFile, writeFile, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import path from "node:path";
+import { spawnSync } from "node:child_process";
+
+for (const scenario of ["success", "baseline", "survives", "missing"]) {
+  test(`mutation gate retains evidence: ${scenario}`, async () => {
+    const root = await mkdtemp(path.join(tmpdir(), "mutation-evidence-test-"));
+    try {
+      await mkdir(path.join(root, "scripts"));
+      await mkdir(path.join(root, "node_modules/vitest"), { recursive: true });
+      await copyFile(path.resolve("scripts/test-accounting-mutations.mjs"), path.join(root, "scripts/test-accounting-mutations.mjs"));
+      await writeFile(path.join(root, "node_modules/vitest/vitest.mjs"), `
+import { writeFileSync } from 'node:fs';
+const name = process.env.PAPERCLIP_ACCOUNTING_MUTATION;
+const scenario = process.env.MUTATION_EVIDENCE_TEST_SCENARIO;
+const titles = { deduplication: 'deduplicates a retried receipt', company: 'isolates company reporting', projection: 'conserves agent projections', threshold: 'stops at the exact budget boundary' };
+console.log(name ? 'ACCOUNTING_MUTATION_APPLIED ' + name : 'baseline diagnostics');
+if (name && scenario === 'missing') process.exit(1);
+const fail = name ? scenario !== 'survives' : scenario === 'baseline';
+const assertionResults = Object.values(titles).map(title => ({ title, status: fail && (!name || title === titles[name]) ? 'failed' : 'passed' }));
+writeFileSync(process.argv.find(arg => arg.startsWith('--outputFile=')).slice(13), JSON.stringify({ testResults: [{ assertionResults }] }));
+process.exit(fail ? 1 : 0);
+`);
+      const result = spawnSync(process.execPath, ["scripts/test-accounting-mutations.mjs"], { cwd: root,
+        env: { ...process.env, MUTATION_EVIDENCE_TEST_SCENARIO: scenario }, encoding: "utf8" });
+      assert.equal(result.status, scenario === "success" ? 0 : 1, result.stderr);
+      const report = JSON.parse(await readFile(path.join(root, "coverage/accounting/mutations.json"), "utf8"));
+      assert.equal(report.evidence.at(-1).result, { success: "killed", baseline: "baseline_failed", survives: "survived_or_invalid", missing: "error" }[scenario]);
+      const last = report.evidence.at(-1).mutation;
+      assert.ok((await readFile(path.join(root, `coverage/accounting/mutations/${last}.log`), "utf8")).length);
+      if (scenario !== "missing") assert.ok(JSON.parse(await readFile(path.join(root, `coverage/accounting/mutations/${last}.json`), "utf8")).testResults.length);
+    } finally { await rm(root, { recursive: true, force: true }); }
+  });
+}