feat(host): adaptive directory-picker default via -auto chooser

Add @deepseek-ai/dsh-host-directory-picker-auto, a node-half-only chooser
that samples the host situation once at boot (bind host via a new
httpServer.host getter, SSH markers, platform, DISPLAY/WAYLAND_DISPLAY)
and mounts the matching dual-face backend (-native or -browse) as a real
Loader entry in the in-memory root tree; the effect disposer removes it.
Entry-level mounting keeps the seam's one-row-swaps-both-faces invariant:
the client module table discovers the mounted backend's browser half
exactly as a config row's. apps/cli now composes -auto as its
directory-picker row; composing a backend row directly remains the pin.

packages/host/directory-picker-auto/src/index.ts

@@ -0,0 +1,52 @@
+/**
+ * Adaptive chooser of the directory-picker seam: resolves the host's
+ * situation once at boot (bind host, SSH launch, display session) and mounts
+ * the matching dual-face backend — `-native` or `-browse` — as a real Loader
+ * entry in the in-memory root tree. Because the backend arrives as an
+ * ordinary entry, its browser half is discovered exactly as a config-row's
+ * would be, so the seam's one-row-swaps-both-faces invariant holds for the
+ * resolved choice; pinning an interaction remains composing that backend row
+ * directly instead of this one.
+ * @module @deepseek-ai/dsh-host-directory-picker-auto
+ */
+
+import type { Context } from 'cordis'
+// Empty type imports carry the `loader` and `httpServer` Context merges for the reads below.
+import type {} from '@cordisjs/plugin-loader'
+import type {} from '@deepseek-ai/dsh-host-webserver'
+import type { DirectoryPickerBackendKind } from './resolve.ts'
+import { resolveDirectoryPickerBackend } from './resolve.ts'
+
+export type { DirectoryPickerBackendKind, DirectoryPickerEnv, DirectoryPickerHostFacts } from './resolve.ts'
+export { resolveDirectoryPickerBackend } from './resolve.ts'
+
+/** Cordis plugin name. */
+export const name = 'directory-picker-auto'
+/** Required services: the effective bind host (`httpServer`) and the entry tree the backend mounts into (`loader`). */
+export const inject = ['httpServer', 'loader']
+
+/** Backend package per resolved kind — fixed composition vocabulary, not a tunable. */
+const BACKEND_PACKAGES: Record<DirectoryPickerBackendKind, string> = {
+  native: '@deepseek-ai/dsh-host-directory-picker-native',
+  browse: '@deepseek-ai/dsh-host-directory-picker-browse',
+}
+
+/**
+ * Resolve the backend from one boot-time sample and mount it as a Loader
+ * entry; the effect's disposer removes the entry, so unloading this plugin
+ * unloads both faces of the mounted backend with it.
+ * @param ctx - cordis context carrying the injected `httpServer` and `loader`.
+ */
+export async function apply(ctx: Context): Promise<void> {
+  const backend = resolveDirectoryPickerBackend({
+    bindHost: ctx.httpServer.host,
+    platform: process.platform,
+    env: process.env,
+  })
+  await ctx.effect(async () => {
+    // Root-tree create: the Loader root is in-memory (write() is a no-op), so
+    // the mounted row can never be persisted back into a config file.
+    const id = await ctx.loader.create({ name: BACKEND_PACKAGES[backend] })
+    return () => { ctx.loader.remove(id) }
+  }, 'directory-picker-auto: backend entry')
+}

packages/host/directory-picker-auto/src/invariant.ts

@@ -0,0 +1,25 @@
+/**
+ * Package-owned invariant companion for the adaptive directory-picker chooser.
+ * @module @deepseek-ai/dsh-host-directory-picker-auto/invariant
+ */
+
+import type { Context } from 'cordis'
+import type { InvariantInstaller } from '@deepseek-ai/dsh-invariants'
+
+const PACKAGE_NAME = '@deepseek-ai/dsh-host-directory-picker-auto'
+
+/** Cordis companion plugin name. */
+export const name = 'host-directory-picker-auto-invariant'
+/** Service required before the companion can reserve package ownership. */
+export const inject = ['invariants']
+
+/** No runtime invariant: the sole effect is one boot-time Loader-entry mount owned by the plugin fiber; the store is authoritative. */
+const install: InvariantInstaller = () => {}
+
+/**
+ * Register the adaptive directory-picker invariant companion.
+ * @param ctx - Cordis context carrying the invariant service.
+ * @returns the installed registration's disposer after setup succeeds.
+ */
+export const apply = (ctx: Context): Promise<() => void> =>
+  Promise.resolve(ctx.invariants.register(PACKAGE_NAME, install))

packages/host/directory-picker-auto/src/resolve.ts

@@ -0,0 +1,46 @@
+/**
+ * Boot-time backend resolution for the adaptive directory-picker composition:
+ * one pure decision from sampled host facts to a concrete backend kind. The
+ * caller samples exactly once per boot, so the mounted capability stays
+ * stable for the service lifetime as the seam requires.
+ * @module @deepseek-ai/dsh-host-directory-picker-auto/resolve
+ */
+
+/** Concrete interaction backend the resolver chooses between. */
+export type DirectoryPickerBackendKind = 'native' | 'browse'
+
+/** Environment keys the resolution reads (a `process.env` subset). */
+export type DirectoryPickerEnv = Readonly<
+  Partial<Record<'SSH_CONNECTION' | 'SSH_TTY' | 'DISPLAY' | 'WAYLAND_DISPLAY', string>>
+>
+
+/** Host facts the backend choice is a pure function of, sampled once at boot. */
+export interface DirectoryPickerHostFacts {
+  /** Effective webserver bind host (`127.0.0.1` or `0.0.0.0`). */
+  bindHost: string
+  /** Host process platform. */
+  platform: NodeJS.Platform
+  /** Environment sample; SSH marks a remote operator, DISPLAY/WAYLAND_DISPLAY a Linux display. */
+  env: DirectoryPickerEnv
+}
+
+/** An env value counts only when set and non-blank (an empty export is "unset" by shell convention). */
+const present = (value: string | undefined): boolean => value !== undefined && value !== ''
+
+/**
+ * Resolve which backend serves this boot. `native` requires every signal that
+ * the operator can see the host display: a loopback-only bind (an
+ * all-interfaces bind admits remote browsers no OS chooser can reach), no SSH
+ * launch (under SSH port-forwarding the chooser would open on the unattended
+ * server), and a display session (assumed on darwin/win32, `DISPLAY`/
+ * `WAYLAND_DISPLAY` elsewhere). Anything ambiguous resolves to `browse`,
+ * which works everywhere.
+ * @param facts - the sampled host facts.
+ * @returns the backend kind to mount.
+ */
+export function resolveDirectoryPickerBackend(facts: DirectoryPickerHostFacts): DirectoryPickerBackendKind {
+  if (facts.bindHost !== '127.0.0.1') return 'browse'
+  if (present(facts.env.SSH_CONNECTION) || present(facts.env.SSH_TTY)) return 'browse'
+  if (facts.platform === 'darwin' || facts.platform === 'win32') return 'native'
+  return present(facts.env.DISPLAY) || present(facts.env.WAYLAND_DISPLAY) ? 'native' : 'browse'
+}