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/index.ts

@@ -48,6 +48,7 @@ import { ContextBuilder, createContextBuilder } from './context';
 import { Mutex, FileLock } from './utils';
 import { FileWatcher, WatchOptions, PendingFile, LockUnavailableError } from './sync';
 import { EXTRACTION_VERSION } from './extraction/extraction-version';
+import { getCodeGraphDir } from './directory';
 import { CodeGraphPackageVersion } from './mcp/version';
 
 // Re-export types for consumers
@@ -154,7 +155,7 @@ export class CodeGraph {
     this.queries = queries;
     this.projectRoot = projectRoot;
     this.fileLock = new FileLock(
-      path.join(projectRoot, '.codegraph', 'codegraph.lock')
+      path.join(getCodeGraphDir(projectRoot), 'codegraph.lock')
     );
     this.orchestrator = new ExtractionOrchestrator(projectRoot, queries);
     this.resolver = createResolver(projectRoot, queries);