fix: orchestrator button + Pi SDK session error

- Move leftSidebarMode from URL state to local useState in unified-shell,
    avoiding force-dynamic router round-trip that made the button appear broken                                           - Replace fileURLToPath(new URL(..., import.meta.url)) with process.cwd()
    in bb-pi-bootstrap.ts — import.meta.url is a webpack:// URL in Next.js,
    causing cross-realm TypeError when passed to Node.js fileURLToPath()

src/lib/agent-workspace.ts

@@ -0,0 +1,41 @@
+import { listProjects } from './registry';
+import { resolveProjectScope } from './project-scope';
+
+export interface ResolveAgentWorkspaceOptions {
+  currentProjectRoot?: string;
+  requestedProjectKey?: string | null;
+  requestedProjectRoot?: string | null;
+}
+
+export interface ResolvedAgentWorkspace {
+  root: string;
+  key: string;
+  source: 'explicit-root' | 'scope-selection';
+}
+
+export async function resolveAgentWorkspace(options: ResolveAgentWorkspaceOptions = {}): Promise<ResolvedAgentWorkspace> {
+  const currentProjectRoot = options.currentProjectRoot ?? process.cwd();
+
+  if (options.requestedProjectRoot && options.requestedProjectRoot.trim()) {
+    const root = options.requestedProjectRoot.trim();
+    return {
+      root,
+      key: root.toLowerCase(),
+      source: 'explicit-root',
+    };
+  }
+
+  const registryProjects = await listProjects();
+  const scope = resolveProjectScope({
+    currentProjectRoot,
+    registryProjects,
+    requestedProjectKey: options.requestedProjectKey ?? null,
+    requestedMode: 'single',
+  });
+
+  return {
+    root: process.platform === 'win32' ? scope.selected.root : scope.selected.displayPath,
+    key: scope.selected.key,
+    source: 'scope-selection',
+  };
+}