feat(directory): CODEGRAPH_DIR env var to override the index dir name (#636) (#741)

Two environments that share one working tree — most concretely Windows
and WSL — can't safely share a single `.codegraph/`: the daemon lockfile
records a platform-specific pid + socket (named pipe vs Unix socket), and
SQLite locking across the WSL2/Windows filesystem boundary is unreliable,
so two daemons over one index risks corruption.

Add a `CODEGRAPH_DIR` env var (default `.codegraph`) that overrides the
per-project data directory name, so each environment keeps its own index
in the same tree (e.g. `CODEGRAPH_DIR=.codegraph-win` on Windows). The
name is resolved live and validated (rejects separators / `..` / absolute,
falling back to the default with a one-time stderr warning). Indexing and
file-watching now skip ANY `.codegraph-*` sibling so neither side trips
over the other's data.

Routes the previously-hardcoded `.codegraph` literals (db path, lockfile,
error log, watcher ignore, file-scan skip, installer) through the
resolver. No extraction-version bump — index content is unchanged.

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

src/sync/watcher.ts

@@ -37,6 +37,7 @@ import type { Ignore } from 'ignore';
 import { isSourceFile, buildDefaultIgnore } from '../extraction';
 import { logDebug, logWarn } from '../errors';
 import { normalizePath } from '../utils';
+import { isCodeGraphDataDir } from '../directory';
 import { watchDisabledReason } from './watch-policy';
 
 /**
@@ -425,8 +426,12 @@ export class FileWatcher {
 
   /** Our own dirs are always ignored, regardless of .gitignore. */
   private isAlwaysIgnored(rel: string): boolean {
+    // First path segment. Ignore any CodeGraph data dir — the active one AND a
+    // sibling like `.codegraph-win` a second environment (Windows/WSL) created
+    // in the same tree, so neither side watches the other's index (#636).
+    const top = rel.split('/')[0] ?? rel;
     return (
-      rel === '.codegraph' || rel.startsWith('.codegraph/') ||
+      isCodeGraphDataDir(top) ||
       rel === '.git' || rel.startsWith('.git/')
     );
   }