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

docs/capability-seams.md

@@ -136,6 +136,10 @@ flowchart LR
   svc_spillStore["ctx.spillStore<br/>Spill storage seam"]
   pkg_spill_local["spill-local"]
   pkg_spill_policy["spill-policy"]
+  pkg_directory_picker["directory-picker"]
+  svc_directoryPicker["ctx.directoryPicker<br/>Workspace-directory picking seam"]
+  pkg_directory_picker_dialog["directory-picker-dialog"]
+  pkg_directory_picker_browse["directory-picker-browse"]
   pkg_webserver["webserver"]
   svc_httpServer["ctx.httpServer<br/>HTTP route registration"]
   pkg_connection["connection"]
@@ -159,6 +163,9 @@ flowchart LR
   pkg_compact --> svc_compact
   pkg_compact_basic --> svc_compact
   pkg_compact_tool_result_prune --> svc_toolResultPrune
+  pkg_directory_picker --> svc_directoryPicker
+  pkg_directory_picker_browse --> svc_directoryPicker
+  pkg_directory_picker_dialog --> svc_directoryPicker
   pkg_fs --> svc_fs
   pkg_fs_local --> svc_fs
   pkg_fs_sandbox --> svc_fs
@@ -235,6 +242,7 @@ flowchart LR
   svc_codeRuntime --> pkg_tools
   svc_commands --> pkg_tui
   svc_compact --> pkg_compact_basic
+  svc_directoryPicker --> pkg_apiproxy
   svc_fs --> pkg_tool_fs
   svc_httpServer --> pkg_connection
   svc_httpServer --> pkg_hmr
@@ -348,6 +356,7 @@ flowchart LR
 | `ctx.tasks` | `seam` | [`tasks`](../packages/tasks/tasks) | [`tasks-local`](../packages/tasks/tasks-local) | [`tool-bash`](../packages/bash/tool-bash), [`tool-pty`](../packages/pty/tool-pty), [`tool-subagent`](../packages/subagent/tool-subagent), [`tool-tasks`](../packages/tasks/tool-tasks) | - | Producers (background bash, PTY sends, and subagent delegations) register running work; tool-tasks is the model-facing control surface that reads, lists, and kills it; tasks-local is the process-local registry. |
 | `ctx.web` | `seam` | [`web`](../packages/web/web) | [`web-search-exa`](../packages/web/web-search-exa), [`web-search-perplexity`](../packages/web/web-search-perplexity), [`web-search-deepseek`](../packages/web/web-search-deepseek), [`web-fetch-local`](../packages/web/web-fetch-local) | [`tool-web`](../packages/web/tool-web) | - | Search and fetch providers register into one ctx.web seam; tool-web owns the stable model-facing names. |
 | `ctx.spillStore` | `seam` | [`spill`](../packages/spill/spill) | [`spill-local`](../packages/spill/spill-local) | [`spill-policy`](../packages/spill/spill-policy) | - | 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. |
+| `ctx.directoryPicker` | `seam` | `directory-picker` | `directory-picker-dialog`, `directory-picker-browse` | `apiproxy` | - | 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. |
 | `ctx.httpServer` | `core` | `webserver` | - | `connection`, `modules`, `hmr` | - | Plain node:http carrier: named-route registry, index transform taps, and the static dist fallback; web-transport plugins register their own routes. |
 | `ctx.clientModuleHost` | `core` | `modules` | - | `hmr` | - | Composes the __DSH_BOOT__ entry graph from an incremental dshClient scan, serves plugin bundles, and notifies rebuilt/graph-changed subscribers. |
 | `ctx.workflows` | `seam` | [`workflow`](../packages/workflow/workflow) | [`workflow-workerthread`](../packages/workflow/workflow-workerthread) | [`tool-workflow`](../packages/workflow/tool-workflow), [`tool-ralph`](../packages/workflow/tool-ralph) | - | One engine per context (bash shape, no named-provider registry); the general workflow and fixed Ralph consumers start runs whose agent() calls fan out through ctx.subagents. |