test(server): make clone-root assertions GITNEXUS_HOME-aware; cover server-mapping fallback

Addresses PR review (#2229):

- git-clone.test.ts hardcoded path.join(os.homedir(), '.gitnexus', 'repos')
  for the clone root, so the "direct child of the clone root" and containment
  assertions failed when GITNEXUS_HOME was set in the ambient env (e.g. a CI
  runner). CLONE_ROOT now derives from getGlobalDir(); mirror that derivation
  via EXPECTED_CLONE_ROOT (GITNEXUS_HOME || ~/.gitnexus), computed at module
  load — the same point CLONE_ROOT is frozen — so the two always agree.

- The GITNEXUS_HOME-unset fallback test covered clone + upload roots but not
  server-mapping (one of the three changed modules). Add a fallback case for
  readServerMapping. It redirects HOME/USERPROFILE to a tmp dir (os.homedir()
  honors them) so it exercises the real ~/.gitnexus fallback without writing
  into the developer's actual ~/.gitnexus/server-mapping.json.

Both files pass with and without GITNEXUS_HOME set.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gitnexus/test/unit/git-clone.test.ts

@@ -32,6 +32,15 @@ import fs from 'node:fs/promises';
 import { spawn } from 'node:child_process';
 import { getRemoteOriginUrl } from '../../src/storage/git.js';
 
+// CLONE_ROOT now derives from getGlobalDir() (GITNEXUS_HOME || ~/.gitnexus), so
+// assertions must mirror that derivation rather than hardcoding ~/.gitnexus —
+// otherwise an ambient GITNEXUS_HOME (e.g. a CI runner that sets it) makes the
+// "direct child of the clone root" assertions fail. Computed at module load,
+// the same point CLONE_ROOT is frozen, so the two always agree.
+const EXPECTED_CLONE_ROOT = path.resolve(
+  path.join(process.env.GITNEXUS_HOME || path.join(os.homedir(), '.gitnexus'), 'repos'),
+);
+
 describe('git-clone', () => {
   describe('extractRepoName', () => {
     it('extracts name from HTTPS URL', () => {
@@ -112,11 +121,9 @@ describe('git-clone', () => {
   });
 
   describe('getCloneDir', () => {
-    it('returns path under ~/.gitnexus/repos/', () => {
+    it('returns path under the clone root (getGlobalDir()/repos/)', () => {
       const dir = getCloneDir('my-repo');
-      expect(dir).toContain('.gitnexus');
-      expect(dir).toMatch(/repos/);
-      expect(dir).toContain('my-repo');
+      expect(dir).toBe(path.join(EXPECTED_CLONE_ROOT, 'my-repo'));
     });
 
     it('rejects ".." to prevent path-traversal escape from the clone root', () => {
@@ -131,7 +138,7 @@ describe('git-clone', () => {
     });
 
     it('returned path is always a direct child of the clone root', () => {
-      const cloneRoot = path.resolve(path.join(os.homedir(), '.gitnexus', 'repos'));
+      const cloneRoot = EXPECTED_CLONE_ROOT;
       const dir = getCloneDir('my-repo');
       const rel = path.relative(cloneRoot, path.resolve(dir));
       // path.relative from the parent to the child must be just the child name —
@@ -476,7 +483,7 @@ describe('git-clone', () => {
     //
     // These tests do NOT mock spawn — the barrier throws synchronously
     // before git is invoked, so the rejection is observable directly.
-    const cloneRoot = path.resolve(path.join(os.homedir(), '.gitnexus', 'repos'));
+    const cloneRoot = EXPECTED_CLONE_ROOT;
 
     it('rejects an absolute target outside CLONE_ROOT', async () => {
       await expect(cloneOrPull('https://github.com/a/b.git', '/etc/passwd')).rejects.toThrow(

gitnexus/test/unit/gitnexus-home-roots.test.ts

@@ -67,4 +67,34 @@ describe('GITNEXUS_HOME path roots', () => {
     );
     expect(UPLOAD_ROOT).toBe(path.resolve(os.homedir(), '.gitnexus', 'uploads'));
   });
+
+  it('server-mapping falls back to ~/.gitnexus when GITNEXUS_HOME is unset', async () => {
+    // os.homedir() honors $HOME (and $USERPROFILE on Windows), so redirect the
+    // home dir to a tmp path to exercise the real fallback (getGlobalDir() ->
+    // ~/.gitnexus) without writing into the developer's actual
+    // ~/.gitnexus/server-mapping.json.
+    const fakeHome = path.join(os.tmpdir(), 'gitnexus-fallback-home');
+    const savedHome = process.env.HOME;
+    const savedUserProfile = process.env.USERPROFILE;
+    delete process.env.GITNEXUS_HOME;
+    process.env.HOME = fakeHome;
+    process.env.USERPROFILE = fakeHome;
+    try {
+      await fs.mkdir(path.join(fakeHome, '.gitnexus'), { recursive: true });
+      await fs.writeFile(
+        path.join(fakeHome, '.gitnexus', 'server-mapping.json'),
+        JSON.stringify({ 'my-repo': 'fallback-service' }),
+        'utf-8',
+      );
+      vi.resetModules();
+      const { readServerMapping } = await import('../../src/core/embeddings/server-mapping.js');
+      expect(await readServerMapping('my-repo')).toBe('fallback-service');
+    } finally {
+      if (savedHome === undefined) delete process.env.HOME;
+      else process.env.HOME = savedHome;
+      if (savedUserProfile === undefined) delete process.env.USERPROFILE;
+      else process.env.USERPROFILE = savedUserProfile;
+      await fs.rm(fakeHome, { recursive: true, force: true });
+    }
+  });
 });