Add uvx support

Add uvx as a supported package manager so that `uvx` commands are
routed through safe-chain's MITM proxy for malware detection, just
like `uv`. Previously, `uvx` bypassed all safe-chain protections.

The uvx package manager reuses the existing uv command runner since
uvx is functionally equivalent to `uv tool run`.

Fixes #268

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/safe-chain/src/packagemanager/currentPackageManager.js

@@ -13,6 +13,7 @@ import { createPipPackageManager } from "./pip/createPackageManager.js";
 import { createUvPackageManager } from "./uv/createUvPackageManager.js";
 import { createPoetryPackageManager } from "./poetry/createPoetryPackageManager.js";
 import { createPipXPackageManager } from "./pipx/createPipXPackageManager.js";
+import { createUvxPackageManager } from "./uvx/createUvxPackageManager.js";
 
 /**
  * @type {{packageManagerName: PackageManager | null}}
@@ -60,6 +61,8 @@ export function initializePackageManager(packageManagerName, context) {
     state.packageManagerName = createPipPackageManager(context);
   } else if (packageManagerName === "uv") {
     state.packageManagerName = createUvPackageManager();
+  } else if (packageManagerName === "uvx") {
+    state.packageManagerName = createUvxPackageManager();
   } else if (packageManagerName === "poetry") {
     state.packageManagerName = createPoetryPackageManager();
   } else if (packageManagerName === "pipx") {

packages/safe-chain/src/packagemanager/uvx/createUvxPackageManager.js

@@ -0,0 +1,18 @@
+import { runUv } from "../uv/runUvCommand.js";
+
+/**
+ * @returns {import("../currentPackageManager.js").PackageManager}
+ */
+export function createUvxPackageManager() {
+  return {
+    /**
+     * @param {string[]} args
+     */
+    runCommand: (args) => {
+      return runUv("uvx", args);
+    },
+    // For uvx, rely solely on MITM
+    isSupportedCommand: () => false,
+    getDependencyUpdatesForCommand: () => [],
+  };
+}

packages/safe-chain/src/packagemanager/uvx/createUvxPackageManager.spec.js

@@ -0,0 +1,14 @@
+import { test } from "node:test";
+import assert from "node:assert";
+import { createUvxPackageManager } from "./createUvxPackageManager.js";
+
+test("createUvxPackageManager returns valid package manager interface", () => {
+  const pm = createUvxPackageManager();
+
+  assert.ok(pm);
+  assert.strictEqual(typeof pm.runCommand, "function");
+  assert.strictEqual(typeof pm.isSupportedCommand, "function");
+  assert.strictEqual(typeof pm.getDependencyUpdatesForCommand, "function");
+  assert.strictEqual(pm.isSupportedCommand(), false);
+  assert.deepStrictEqual(pm.getDependencyUpdatesForCommand(), []);
+});