test(config): ensure no duplicate environment variable names (renovatebot#42204)

As we continue to be more careful with our environment variable usage,
we should make sure it's not possible to ever have a clash.

Co-authored-by: Claude Sonnet 4.6 <jamie.tanna+claude-code@mend.io>

Author: jamietanna

lib/workers/global/config/parse/env.spec.ts

@@ -1,4 +1,5 @@
 import type { MockInstance } from 'vitest';
+import { getOptions } from '../../../../config/options/index.ts';
 import type { RequiredConfig } from '../../../../config/types.ts';
 import { logger } from '../../../../logger/index.ts';
 import * as env from './env.ts';
@@ -391,6 +392,27 @@ describe('workers/global/config/parse/env', () => {
     });
   });
 
+  it('has no duplicate env names across options', () => {
+    const options = getOptions();
+    const envNameToOptions = new Map<string, string[]>();
+
+    for (const option of options) {
+      const envName = env.getEnvName(option);
+      if (envName === '') {
+        continue;
+      }
+      const existing = envNameToOptions.get(envName) ?? [];
+      existing.push(option.name);
+      envNameToOptions.set(envName, existing);
+    }
+
+    const duplicates = [...envNameToOptions.entries()]
+      .filter(([, names]) => names.length > 1)
+      .map(([envName, names]) => `${envName}: ${names.join(', ')}`);
+
+    expect(duplicates).toEqual([]);
+  });
+
   describe('.getEnvName(definition)', () => {
     it('returns empty', () => {
       const option: ParseConfigOptions = {