test(security): prove UTF-16 truncation boundaries

steipete · steipete · commit 6cf25a8c6751 · 2026-07-09T06:22:12.000+01:00
diff --git a/src/security/channel-metadata.test.ts b/src/security/channel-metadata.test.ts
@@ -0,0 +1,46 @@
+// Covers bounded, untrusted channel metadata construction.
+import { describe, expect, it } from "vitest";
+import { buildUntrustedChannelMetadata } from "./channel-metadata.js";
+
+function normalizeMarkerIds(value: string): string {
+  return value.replace(/id="[a-f0-9]{16}"/g, 'id="<id>"');
+}
+
+function wrapExpected(content: string): string {
+  return [
+    "",
+    '<<<EXTERNAL_UNTRUSTED_CONTENT id="<id>">>>',
+    "Source: Channel metadata",
+    "---",
+    content,
+    '<<<END_EXTERNAL_UNTRUSTED_CONTENT id="<id>">>>',
+  ].join("\n");
+}
+
+describe("buildUntrustedChannelMetadata", () => {
+  it("keeps per-entry truncation UTF-16 safe", () => {
+    const entryPrefix = "a".repeat(396);
+    const result = buildUntrustedChannelMetadata({
+      source: "test",
+      label: "Test channel",
+      entries: [`${entryPrefix}🎉tail`],
+    });
+
+    expect(normalizeMarkerIds(result ?? "")).toBe(
+      wrapExpected(`UNTRUSTED channel metadata (test)\nTest channel:\n${entryPrefix}...`),
+    );
+  });
+
+  it("keeps the combined metadata limit UTF-16 safe", () => {
+    const header = "UNTRUSTED channel metadata (test)\nTest channel:\n";
+    const entryPrefix = "short";
+    const result = buildUntrustedChannelMetadata({
+      source: "test",
+      label: "Test channel",
+      entries: [`${entryPrefix}🎉tail`],
+      maxChars: header.length + entryPrefix.length + 4,
+    });
+
+    expect(normalizeMarkerIds(result ?? "")).toBe(wrapExpected(`${header}${entryPrefix}...`));
+  });
+});
diff --git a/src/security/install-policy.test.ts b/src/security/install-policy.test.ts
@@ -355,6 +355,25 @@ describe("runInstallPolicy", () => {
     expect(warnings.join("\n")).toContain("blocked by install policy");
   });
 
+  it("keeps truncated operator block reasons UTF-16 safe", async () => {
+    const reasonPrefix = "r".repeat(999);
+    const result = await runInstallPolicy({
+      config: configWithPolicy(scriptPath, {
+        POLICY_RESPONSE: JSON.stringify({
+          protocolVersion: 1,
+          decision: "block",
+          reason: `${reasonPrefix}🎉tail`,
+        }),
+      }),
+      request: baseRequest(sourceDir),
+    });
+
+    expect(result?.blocked).toEqual({
+      code: "security_scan_blocked",
+      reason: `blocked by install policy: ${reasonPrefix}...`,
+    });
+  });
+
   it("preserves allow findings without file or line", async () => {
     const result = await runInstallPolicy({
       config: configWithPolicy(scriptPath, {
diff --git a/test/security/channel-metadata.test.ts b/test/security/channel-metadata.test.ts
