feat(host): directory-picker capability seam with dialog and browse backends

The web GUI's folder picking was hardwired to one interaction: a native
OS chooser compiled into the gateway, unusable for remote deployments
and swappable only by editing apiproxy source.

Directory picking becomes a three-package capability seam in
packages/host: ctx.directoryPicker returns a discriminated capability —
dialog (the extracted native chooser; host-display only) or browse
(new: one-level listing + child creation over Node stdlib, hidden flags
host-stamped, symlinks followed, ancestry crumbs; remote-capable). The
gateway injects the seam, advertises the kind via
host.describe.directoryPicker, serves host.listDirectory /
host.createDirectory under browse, and answers
directory-picker-unavailable across kinds. cordis.yml is the swap
point; apps/cli keeps dialog mounted, so behavior is unchanged until
the in-app browser PR flips the default. The connection fixture serves
a deterministic browse tree; WorkspacesService gains the browse calls
the browser UI will drive. Decision record:
.agents/notes/implemented/architecture/2026-07-28-directory-picker-capability-seam.md

scripts/gen-doc-graphs.ts

@@ -408,6 +408,15 @@ const SERVICE_ROLES: ServiceRole[] = [
     consumers: ['spill-policy'],
     note: 'The backend saves oversized tool text and returns a model-facing locator plus retrieval hint; spill-policy is the tools/post-execute consumer that decides when to spill.',
   },
+  {
+    key: 'directoryPicker',
+    pkg: 'directory-picker',
+    title: 'Workspace-directory picking seam',
+    mode: 'seam',
+    implementations: ['directory-picker-dialog', 'directory-picker-browse'],
+    consumers: ['apiproxy'],
+    note: 'Discriminated interaction capability: the dialog backend opens one native OS chooser on the host display, the browse backend serves listing/creation primitives for the in-app browser; the gateway advertises the kind via host.describe.',
+  },
   {
     key: 'httpServer',
     pkg: 'webserver',