fix(proxy): route through undici's own fetch and keep undici external

Corporate-proxy users could not connect to any remote MCP server from v2.
Two independent defects, both reported in #2067.

1. The web and TUI bundles inlined undici. It was declared in the root and
   `clients/cli` manifests but named in no client's tsup `external` list, and
   tsup auto-externalizes only what the *nearest* manifest declares — so
   esbuild inlined 1.05MB of it into `clients/{web,tui}/build/`. undici is
   CommonJS, so the emitted chunk's `require("assert")` hit esbuild's ESM
   `__require` shim and threw `Dynamic require of "assert" is not supported`.
   The rejected `import()` surfaced as "the `undici` package is not available",
   telling users to install a package that was already present — and could not
   have helped, because the specifier had been rewritten to a relative chunk at
   build time.

2. `withProxyDispatcher` injected a *userland* undici `EnvHttpProxyAgent` into
   Node's *built-in* fetch. That couples two different copies of undici at the
   dispatcher handler interface, which is not stable across majors: Node 22
   embeds undici 6, Node 24 embeds 7, Node 26 embeds 8. A userland undici 8
   agent handed a built-in undici 7 handler is rejected with
   `fetch failed: invalid onRequestStart method`, and the request never leaves
   the process. So fixing the bundling alone would only have converted the
   web/TUI failure into the CLI's.

Both halves of the pair now come from userland undici — its `fetch` and its
`EnvHttpProxyAgent` — which keeps the handler inside one copy and works
unchanged from the Node 22.19 engine floor through Node 26. Deleting the
wrapper in favor of Node's native `NODE_USE_ENV_PROXY` was not an option:
measured, it is unsupported on 22.19 (the floor) and only lands mid-22.x.

Because undici's `Response` is a different class from `globalThis.Response`,
the proxied fetch re-wraps each response as a genuine global `Response`,
streaming preserved. Without that, `res instanceof Response` is false for
callers that test it — including the SDK's OAuth error formatter, which would
degrade every message to `Raw body: [object Response]`.

The proxy now sits at the bottom of the fetch stack (`environment.fetch` for
the Node clients, and the `createTransportNode` default for the web backend,
its one caller that supplies no `fetchFn`) rather than wrapping the transport's
fetch. Proxying means *substituting* the fetch, not decorating one, so wrapping
a supplied `fetchFn` would discard it; installing it underneath lets
InspectorClient's own wrappers compose over it. A side effect worth having:
OAuth discovery and token requests go through `environment.fetch` too, and were
never proxied before.

Guarding it:

- `undici` is added to all three tsup `external` lists and removed from
  `clients/cli/package.json`, so it is root-declared only, per the placement
  rule in AGENTS.md. The two installs had already drifted (root 8.5.0 vs cli
  8.9.0).
- New `npm run verify:bundle-externals` fails if any package a client declares
  external was inlined into that client's bundle anyway. It reads the *built
  output*, not the config — those two disagreed for four releases — and derives
  what to check from each client's own `external` array, so a newly
  externalized package is covered without editing the guard. Verified against
  the real pre-fix artifact, which it flags.
- The proxy tests now drive a real forwarding proxy rather than a mock. That
  matters: defect 2 was a runtime interface mismatch, which no mock can catch
  because no mock ever dispatches.

AGENTS.md's must-not-bundle rule (added by #2082) is extended with why undici
slipped past it, and notes the `node -e` trap — probing the bundled chunk with
`node -e` falsely succeeds, because it exposes a global `require` that
satisfies esbuild's guard.

Closes #2067

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>

clients/tui/__tests__/App.test.tsx

@@ -232,6 +232,10 @@ vi.mock("@inspector/core/mcp/state/index.js", () => ({
 }));
 vi.mock("@inspector/core/mcp/node/index.js", () => ({
   createTransportNode: vi.fn(),
+  // Returns undefined for "no proxy configured", which is what the real one
+  // does with no proxy env var set — so `environment.fetch` stays unset and the
+  // client falls back to the built-in fetch, exactly as before #2067.
+  createProxyFetch: vi.fn(() => undefined),
 }));
 vi.mock("@inspector/core/react/useInspectorClient.js", () => ({
   useInspectorClient: h.useInspectorClient,

clients/tui/src/App.tsx

@@ -31,7 +31,10 @@ import {
   FetchRequestLogState,
   StderrLogState,
 } from "@inspector/core/mcp/state/index.js";
-import { createTransportNode } from "@inspector/core/mcp/node/index.js";
+import {
+  createProxyFetch,
+  createTransportNode,
+} from "@inspector/core/mcp/node/index.js";
 import { useInspectorClient } from "@inspector/core/react/useInspectorClient.js";
 import { useManagedTools } from "@inspector/core/react/useManagedTools.js";
 import { useManagedResources } from "@inspector/core/react/useManagedResources.js";
@@ -290,6 +293,10 @@ function App({
         const environment: InspectorClientEnvironment = {
           transport: createTransportNode,
           logger: getTuiLogger(),
+          // Bottom of the fetch stack, so InspectorClient's wrappers compose
+          // over it and OAuth requests are proxied too (#2067). Undefined when
+          // no proxy env var is set.
+          fetch: createProxyFetch(),
         };
         const defaultMetadata = savedSettings?.metadata
           ? Object.fromEntries(

clients/tui/tsup.config.ts

@@ -99,6 +99,14 @@ export default defineConfig({
   // `__tests__/tsupConfig.test.ts` guards this list.
   noExternal: [/^@inspector\/core/, "ink-form", "ink-scroll-view"],
   external: [
+    // `undici` MUST stay external. It is CommonJS, so inlining it rewrites
+    // `import("undici")` to a relative chunk whose `require("assert")` hits
+    // esbuild's ESM `__require` shim and throws "Dynamic require of \"assert\"
+    // is not supported" — and because the specifier was rewritten at build time,
+    // no user-side install can ever satisfy it (#2067). It is declared in the
+    // ROOT manifest only, so tsup cannot infer this from a nearest-manifest
+    // lookup; the entry has to be explicit.
+    "undici",
     // `react` is deliberately external — the single instance every inlined
     // package above resolves to, from this build directory.
     "react",