fix(watch): accept -d/--db to point at a graph.db outside cwd (#987)

Every other command that operates on a graph DB (build, stats, query,
fn-impact, impact, etc.) accepts \`-d, --db <path>\`, but \`watch\` did
not — it rejected the flag with \`error: unknown option '--db'\` and
only honored the positional \`[dir]\`. This forced users in monorepo
and multi-repo setups to \`cd\` into the watched directory, defeating
the purpose of having \`--db\` elsewhere.

Add the option to the watch command, plumb it through watchProject
and setupWatcher, and fall back to \`<rootDir>/.codegraph/graph.db\`
when \`--db\` is absent.

Closes #984

Author: carlos-alm

src/cli/commands/watch.ts

@@ -6,6 +6,7 @@ export const command: CommandDefinition = {
   name: 'watch [dir]',
   description: 'Watch project for file changes and incrementally update the graph',
   options: [
+    ['-d, --db <path>', 'Path to graph.db'],
     ['--poll', 'Use stat-based polling (default on Windows to avoid ReFS/Dev Drive crashes)'],
     ['--native', 'Force native OS file watchers instead of polling'],
     ['--poll-interval <ms>', 'Polling interval in milliseconds (default: 2000)'],
@@ -22,6 +23,7 @@ export const command: CommandDefinition = {
       engine,
       poll,
       pollInterval: opts.pollInterval ? Number(opts.pollInterval) : undefined,
+      dbPath: opts.db ? path.resolve(opts.db) : undefined,
     });
   },
 };

src/domain/graph/watcher.ts

@@ -165,8 +165,8 @@ interface WatcherContext {
 }
 
 /** Initialize DB, engine, cache, and statements for watch mode. */
-function setupWatcher(rootDir: string, opts: { engine?: string }): WatcherContext {
-  const dbPath = path.join(rootDir, '.codegraph', 'graph.db');
+function setupWatcher(rootDir: string, opts: { engine?: string; dbPath?: string }): WatcherContext {
+  const dbPath = opts.dbPath ?? path.join(rootDir, '.codegraph', 'graph.db');
   if (!fs.existsSync(dbPath)) {
     throw new DbError('No graph.db found. Run `codegraph build` first.', { file: dbPath });
   }
@@ -297,7 +297,7 @@ function setupShutdownHandler(ctx: WatcherContext, cleanup: () => void): void {
 
 export async function watchProject(
   rootDir: string,
-  opts: { engine?: string; poll?: boolean; pollInterval?: number } = {},
+  opts: { engine?: string; poll?: boolean; pollInterval?: number; dbPath?: string } = {},
 ): Promise<void> {
   const ctx = setupWatcher(rootDir, opts);