fix(installer,cli): refuse to index $HOME / filesystem root (#860)

Running the installer or `codegraph init`/`index` from $HOME auto-indexed the
entire home tree (installer indexes process.cwd() with no guard), producing a
multi-GB ~/.codegraph/codegraph.db; the install dir sharing the ~/.codegraph
name then made every home subdir resolve its root to $HOME. On pre-1.0 macOS the
per-file watcher over that tree exhausted kern.maxfiles and crashed the machine
(#845; the fd blowup was fixed in 1.0.0, this fixes the root cause).

Add unsafeIndexRootReason() and refuse the home dir, a parent of home, and
filesystem roots at the installer auto-index, `init`, and `index`. Overridable
with --force. Closes #845.

src/installer/index.ts

@@ -28,7 +28,7 @@ import { getGlyphs } from '../ui/glyphs';
 // installer must stay importable even when native modules can't load).
 import { watchDisabledReason } from '../sync/watch-policy';
 import { isGitRepo, isSyncHookInstalled, installGitSyncHook } from '../sync/git-hooks';
-import { getCodeGraphDir, codeGraphDirName } from '../directory';
+import { getCodeGraphDir, codeGraphDirName, unsafeIndexRootReason } from '../directory';
 import { getTelemetry, recordIndexEvent, TELEMETRY_DOCS } from '../telemetry';
 
 // Backwards-compat: keep these named exports — downstream code may
@@ -501,6 +501,18 @@ async function initializeLocalProject(
 ): Promise<void> {
   const projectPath = process.cwd();
 
+  // Never auto-index the home directory or a filesystem root. Running the
+  // installer from `$HOME` would otherwise index the entire home tree — a
+  // multi-GB index, constant watcher churn, and (pre-1.0 on macOS) fd
+  // exhaustion that crashed the machine (#845). The install itself still
+  // completes; we just skip the auto-index and point them at a real project.
+  const unsafe = unsafeIndexRootReason(projectPath);
+  if (unsafe) {
+    clack.log.warn(`Skipping automatic indexing — ${projectPath} looks like ${unsafe}.`);
+    clack.log.info('Indexing it would pull in caches, other projects, and your whole tree. Run "codegraph init" inside a specific project instead.');
+    return;
+  }
+
   let CodeGraph: typeof import('../index').default;
   try {
     CodeGraph = (await import('../index')).default;