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

packages/cordis/tool-cordis/src/api-catalog.ts

@@ -260,6 +260,16 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
       },
     ],
   },
+  {
+    key: 'directoryPicker',
+    summary: 'Abstract directory-picking service.',
+    methods: [
+      {
+        signature: 'abstract capability(): DirectoryPickerCapability',
+        jsDoc: '/**\n * The backend\'s interaction capability.\n * @returns the discriminated capability consumers switch on.\n */',
+      },
+    ],
+  },
   {
     key: 'fs',
     summary: 'Abstract filesystem provider.',
@@ -1581,6 +1591,26 @@ export const TYPE_API: readonly TypeApiEntry[] = [
     name: 'DiffResultView',
     declaration: 'export interface DiffResultView {\n    card: \'diff\';\n    title?: string;\n    diffs: FileDiff[];\n}',
   },
+  {
+    name: 'DirectoryEntry',
+    declaration: 'export interface DirectoryEntry {\n    name: string;\n    path: string;\n    hidden: boolean;\n}',
+  },
+  {
+    name: 'DirectoryListing',
+    declaration: 'export interface DirectoryListing {\n    path: string;\n    home: string;\n    crumbs: DirectoryEntry[];\n    entries: DirectoryEntry[];\n}',
+  },
+  {
+    name: 'DirectoryPickerBrowseCapability',
+    declaration: 'export interface DirectoryPickerBrowseCapability {\n    kind: \'browse\';\n    list(path?: string): Promise<DirectoryListing>;\n    createDirectory(path: string, name: string): Promise<string>;\n}',
+  },
+  {
+    name: 'DirectoryPickerCapability',
+    declaration: 'export type DirectoryPickerCapability = DirectoryPickerDialogCapability | DirectoryPickerBrowseCapability;',
+  },
+  {
+    name: 'DirectoryPickerDialogCapability',
+    declaration: 'export interface DirectoryPickerDialogCapability {\n    kind: \'dialog\';\n    pick(signal: AbortSignal): Promise<string | null>;\n}',
+  },
   {
     name: 'Domain',
     declaration: 'export interface Domain<S extends DomainSpec> {\n    readonly name: string;\n    readonly global: DomainGlobalHandleOf<S>;\n    table<N extends keyof S[\'tables\'] & string>(name: N): KvTable<TableKeyOf<S, N>, TableValueOf<S, N>>;\n    close(): Promise<void>;\n}',