test(stack): assert clerkJwtProvider throws when its token env var is unset

Closes the review gap: the identity suites' "fail rather than skip" contract
rests on clerkJwtProvider throwing when CLERK_MACHINE_TOKEN is unset, but nothing
asserted it — a weakening to a skip/undefined would take the identity suite dark
while CI stayed green. The throw fires before createClerkClient, so this is a
credential-free unit test.

Claude-Session: https://claude.ai/code/session_01MxTTPaPP16m6br7Hoab94w

Author: coderdan

packages/stack/__tests__/clerk-provider.test.ts

@@ -0,0 +1,33 @@
+import { afterEach, describe, expect, it } from 'vitest'
+import { clerkJwtProvider } from '../integration/helpers/clerk'
+
+/**
+ * `clerkJwtProvider`'s "FAIL rather than skip" guard is the load-bearing half of
+ * the identity suites' no-silent-skip contract: if it were ever weakened to a
+ * skip or a silent `undefined`, the entire identity suite would go dark while CI
+ * stayed green. The throw is pure logic — it fires before `createClerkClient`,
+ * so it needs no live Clerk and belongs here in the credential-free unit suite
+ * rather than the integration config (which only globs `*.integration.test.ts`).
+ */
+describe('clerkJwtProvider', () => {
+  const saved = process.env.CLERK_MACHINE_TOKEN
+  const savedB = process.env.CLERK_MACHINE_TOKEN_B
+  afterEach(() => {
+    if (saved === undefined) delete process.env.CLERK_MACHINE_TOKEN
+    else process.env.CLERK_MACHINE_TOKEN = saved
+    if (savedB === undefined) delete process.env.CLERK_MACHINE_TOKEN_B
+    else process.env.CLERK_MACHINE_TOKEN_B = savedB
+  })
+
+  it('throws (does not skip) when the default machine token env var is unset', () => {
+    delete process.env.CLERK_MACHINE_TOKEN
+    expect(() => clerkJwtProvider()).toThrow(/missing CLERK_MACHINE_TOKEN/)
+  })
+
+  it('names the custom env var it was handed', () => {
+    delete process.env.CLERK_MACHINE_TOKEN_B
+    expect(() => clerkJwtProvider('CLERK_MACHINE_TOKEN_B')).toThrow(
+      /CLERK_MACHINE_TOKEN_B/,
+    )
+  })
+})