test(proxy): isolate proxy env per suite; fail the bundle guard closed

Addresses review round 2 on #2099.

- The /api/fetch proxy test set only uppercase HTTP_PROXY, so an ambient
  lowercase `http_proxy` (which undici's EnvHttpProxyAgent prefers) or a NO_PROXY
  could route the request elsewhere and fail the assertion. All six proxy vars
  are now saved and cleared for the whole /api/fetch suite and restored in
  afterAll — suite-level rather than per-test because the agent is memoized
  process-wide once built. Verified the test still passes under a deliberately
  hostile ambient env (`http_proxy=http://127.0.0.1:9 NO_PROXY='*'`).

- `verify:bundle-externals` reported success when `parseExternals` returned
  nothing, so an ordinary tsup refactor — hoisting the array to a constant, or a
  line break after `external:` — would silently disable the guard. It now fails
  closed: every bundled client has externals, so "none parsed" means the parser
  lost track of the config. Verified against exactly that refactor. The
  per-client verdict moved into a pure `evaluateClient()` so all three failure
  modes are unit-tested, and the failure epilogue is now printed only for a real
  inlining, since "add the package to `external`" is the wrong instruction for
  the other two.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JTHVxSu8AUgHRLvo1ntZ8H
Signed-off-by: cliffhall <cliff@futurescale.com>

scripts/verify-bundle-externals.test.mjs

@@ -12,6 +12,7 @@ import assert from "node:assert/strict";
 
 import {
   BUNDLED_CLIENTS,
+  evaluateClient,
   parseExternals,
   findInlinedExternals,
 } from "./verify-bundle-externals.mjs";
@@ -152,6 +153,71 @@ describe("findInlinedExternals", () => {
   });
 });
 
+describe("evaluateClient", () => {
+  const banner = (p) => `// ${p}\nvar x = 1;\n`;
+  const clean = [
+    { name: "index.js", source: banner("../../core/mcp/index.ts") },
+  ];
+
+  test("fails closed when no externals could be parsed", () => {
+    // A tsup refactor — `external: EXTERNALS`, or a line break after the colon —
+    // makes parseExternals return nothing. Checking zero packages and reporting
+    // success would silently disable the guard on a change that looks harmless.
+    const failures = evaluateClient({
+      name: "web",
+      build: "clients/web/build",
+      externals: [],
+      files: clean,
+    });
+    assert.equal(failures.length, 1);
+    assert.match(failures[0], /no `external` entries could be parsed/);
+  });
+
+  test("fails when the bundle carries no module banners", () => {
+    const failures = evaluateClient({
+      name: "cli",
+      build: "clients/cli/build",
+      externals: ["undici"],
+      files: [{ name: "index.js", source: "var a=1;" }],
+    });
+    assert.equal(failures.length, 1);
+    assert.match(failures[0], /no esbuild module banners/);
+  });
+
+  test("reports one failure per inlined package", () => {
+    const failures = evaluateClient({
+      name: "tui",
+      build: "clients/tui/build",
+      externals: ["undici", "pino"],
+      files: [
+        {
+          name: "index.js",
+          source:
+            banner("../../node_modules/undici/index.js") +
+            banner("../../node_modules/pino/pino.js"),
+        },
+      ],
+    });
+    assert.equal(failures.length, 2);
+    assert.match(
+      failures[0],
+      /tui: "undici" is declared external but was inlined/,
+    );
+  });
+
+  test("passes a clean bundle", () => {
+    assert.deepEqual(
+      evaluateClient({
+        name: "web",
+        build: "clients/web/build",
+        externals: ["undici"],
+        files: clean,
+      }),
+      [],
+    );
+  });
+});
+
 describe("BUNDLED_CLIENTS", () => {
   test("covers every tsup-bundled client", () => {
     // `clients/launcher` is plain tsc and emits no bundle, so it is deliberately