fix(host,client): stream bounded listings, declare schemastery, guard Choose again

The browse level now streams through opendir into a name-sorted window of
maxEntries + 1 candidates (boundedInsert), so memory stays O(maxEntries)
no matter how many children a directory holds and enterability probing
touches only windowed candidates; a windowed broken symlink is not
backfilled since the eviction already marks the level truncated.
schemastery joins the package's runtime dependencies (the source launcher
and isolated installs failed to resolve the value import). The
folder-error dialog's Choose again goes inert while the flow hole is
empty, and the withdrawal effect also keys on the open transition, so a
flow can never open over a hole nobody serves.

packages/host/directory-picker-browse/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/host/directory-picker-browse/README.md
-README.md: 2f1994100f0fb8fcadae46094267057b3966197e
-README.zh.md: a149133a13ca99f176680c68b4931b9673f4aaa8
+README.md: 155b18eecb46d704dc181e29fdf7eb67fac42839
+README.zh.md: 154eeb571171116ae98e46efe77efd45986f67ea

packages/host/directory-picker-browse/README.md

@@ -4,7 +4,7 @@ English | [中文](README.zh.md)
 
 The **in-app browsing backend** of the [directory-picker seam](../directory-picker/README.md): `BrowseDirectoryPicker` registers `ctx.directoryPicker` with the `browse` capability — one-level directory listing and child-directory creation over Node's stdlib, which already carries the per-OS adaptation. Nothing renders on the host display, so this backend serves remote clients the native backend cannot.
 
-Behavior facts: listings return **directories only**, name-sorted, with symlinks-to-directories followed (broken/cyclic links skipped — the probe `stat` failing means "not enterable") and a host-owned `hidden` flag (POSIX dot convention) left for the client to act on; `crumbs` is the root-to-target ancestor chain, the root crumb labeled by its full path (`/`, `C:\`); an absent `list` path means the host account's home directory. `createDirectory` is non-recursive (a missing parent is a real failure, not a level to invent) and validates the name as a single non-blank segment even when called directly, mirroring the wire schema's fence. Both primitives reject an explicit path that is not fully qualified — relative forms, and on Windows the rooted drive-less forms (`\foo`, `/foo`) and incomplete UNC prefixes (`\\`, `\\server`) that `isAbsolute` accepts — with `directory-unreadable`/`directory-create-failed`, instead of letting `resolve` rebase it under the host process cwd or current drive. One `list` call materializes at most `maxEntries` rows (config, default 1000 — the bound GitHub's web UI applies to directory listings): a cut level keeps the name-sorted head, counts hidden rows against the bound, stops probing once the bound is hit, and reports `truncated: true` so the client can say the level is incomplete. Failures throw the seam's typed `DirectoryPickerError`. Policy rationale: [the directory-picker capability seam Agent Note](../../../.agents/notes/implemented/architecture/2026-07-28-directory-picker-capability-seam.md).
+Behavior facts: listings return **directories only**, name-sorted, with symlinks-to-directories followed (broken/cyclic links skipped — the probe `stat` failing means "not enterable") and a host-owned `hidden` flag (POSIX dot convention) left for the client to act on; `crumbs` is the root-to-target ancestor chain, the root crumb labeled by its full path (`/`, `C:\`); an absent `list` path means the host account's home directory. `createDirectory` is non-recursive (a missing parent is a real failure, not a level to invent) and validates the name as a single non-blank segment even when called directly, mirroring the wire schema's fence. Both primitives reject an explicit path that is not fully qualified — relative forms, and on Windows the rooted drive-less forms (`\foo`, `/foo`) and incomplete UNC prefixes (`\\`, `\\server`) that `isAbsolute` accepts — with `directory-unreadable`/`directory-create-failed`, instead of letting `resolve` rebase it under the host process cwd or current drive. One `list` call returns at most `maxEntries` rows (config, default 1000 — the bound GitHub's web UI applies to directory listings), and the level streams through a bounded window so memory stays O(maxEntries) no matter how many children the directory holds: a cut level keeps the name-sorted head, counts hidden rows against the bound, probes only windowed candidates, and reports `truncated: true` so the client can say the level is incomplete (a windowed broken symlink is not backfilled from beyond the window — the eviction already marks the level truncated). Failures throw the seam's typed `DirectoryPickerError`. Policy rationale: [the directory-picker capability seam Agent Note](../../../.agents/notes/implemented/architecture/2026-07-28-directory-picker-capability-seam.md).
 
 ## Model Experience
 

packages/host/directory-picker-browse/README.zh.md

@@ -4,7 +4,7 @@
 
 [目录选择 seam](../directory-picker/README.md) 的**应用内浏览后端**：`BrowseDirectoryPicker` 以 `browse` 能力注册 `ctx.directoryPicker`——基于 Node 标准库（跨 OS 适配本就由它承担）提供单层目录列举与子目录创建。宿主屏幕上不渲染任何东西，因此该后端能服务 native 后端无法触及的远程客户端。
 
-行为事实：列举**只返回目录**、按名称排序，指向目录的符号链接会被跟随（断链／循环链接被跳过——探测 `stat` 失败即"不可进入"），并携带宿主判定的 `hidden` 标志（POSIX 点前缀约定），展示决策留给客户端；`crumbs` 是从根到目标的祖先链，根 crumb 以完整路径标注（`/`、`C:\`）；`list` 不带路径即列举宿主账户的家目录。`createDirectory` 不递归（父目录缺失是真实失败，不是要补造的层级），且即便被直接调用也把名称校验为单个非空段，与协议 schema 的栅栏一致。两个原语都拒绝非完全限定的显式路径——相对形态，以及 Windows 上 `isAbsolute` 会放行的无盘符有根形态（`\foo`、`/foo`）与不完整的 UNC 前缀（`\\`、`\\server`）——报 `directory-unreadable`／`directory-create-failed`，而不是任由 `resolve` 把它重定位到宿主进程 cwd 或当前盘符之下。单次 `list` 至多物化 `maxEntries` 行（配置项，默认 1000——GitHub 网页端对目录列举采用的同一上限）：被截断的层级保留按名排序的头部、隐藏行计入上限、达到上限即停止探测，并报告 `truncated: true`，供客户端提示层级不完整。失败抛出 seam 的类型化 `DirectoryPickerError`。策略依据：[目录选择能力 seam Agent Note](../../../.agents/notes/implemented/architecture/2026-07-28-directory-picker-capability-seam.md)。
+行为事实：列举**只返回目录**、按名称排序，指向目录的符号链接会被跟随（断链／循环链接被跳过——探测 `stat` 失败即"不可进入"），并携带宿主判定的 `hidden` 标志（POSIX 点前缀约定），展示决策留给客户端；`crumbs` 是从根到目标的祖先链，根 crumb 以完整路径标注（`/`、`C:\`）；`list` 不带路径即列举宿主账户的家目录。`createDirectory` 不递归（父目录缺失是真实失败，不是要补造的层级），且即便被直接调用也把名称校验为单个非空段，与协议 schema 的栅栏一致。两个原语都拒绝非完全限定的显式路径——相对形态，以及 Windows 上 `isAbsolute` 会放行的无盘符有根形态（`\foo`、`/foo`）与不完整的 UNC 前缀（`\\`、`\\server`）——报 `directory-unreadable`／`directory-create-failed`，而不是任由 `resolve` 把它重定位到宿主进程 cwd 或当前盘符之下。单次 `list` 至多返回 `maxEntries` 行（配置项，默认 1000——GitHub 网页端对目录列举采用的同一上限），且层级以流式方式经过一个有界窗口，无论目录有多少子项内存都保持 O(maxEntries)：被截断的层级保留按名排序的头部、隐藏行计入上限、只探测窗口内候选，并报告 `truncated: true`，供客户端提示层级不完整（窗口内的断链符号链接不会从窗口外回填——发生过驱逐本身已把层级标记为截断）。失败抛出 seam 的类型化 `DirectoryPickerError`。策略依据：[目录选择能力 seam Agent Note](../../../.agents/notes/implemented/architecture/2026-07-28-directory-picker-capability-seam.md)。
 
 ## 模型体验
 

packages/host/directory-picker-browse/package.json

@@ -27,7 +27,8 @@
   ],
   "license": "BSD-3-Clause",
   "dependencies": {
-    "@deepseek-ai/dsh-host-directory-picker": "workspace:^"
+    "@deepseek-ai/dsh-host-directory-picker": "workspace:^",
+    "schemastery": "^3.18.0"
   },
   "peerDependencies": {
     "@deepseek-ai/dsh-invariants": "^0.0.1",

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

@@ -9,7 +9,7 @@
  * @module @deepseek-ai/dsh-host-directory-picker-browse
  */
 
-import { mkdir, readdir, stat } from 'node:fs/promises'
+import { mkdir, opendir, stat } from 'node:fs/promises'
 import { homedir } from 'node:os'
 import { basename, dirname, join, posix, resolve, win32 } from 'node:path'
 import type { Context } from 'cordis'
@@ -53,6 +53,35 @@ export function fullyQualified(path: string, platform: NodeJS.Platform = process
     : posix.isAbsolute(path)
 }
 
+/** One streamed listing candidate: the dirent facts a row needs, nothing else retained. */
+export interface ListingCandidate {
+  /** Base name within the streamed level. */
+  name: string
+  /** Dirent says directory (no probe needed). */
+  isDirectory: boolean
+  /** Dirent says symlink (enterability needs a stat probe). */
+  isSymbolicLink: boolean
+}
+
+/**
+ * Insert a streamed candidate into the name-sorted bounded window, evicting
+ * the name-largest candidate when the window exceeds `keep`. Memory over an
+ * arbitrarily large level therefore stays O(keep) regardless of how many
+ * children the directory holds.
+ * @param window - the name-ascending window, mutated in place.
+ * @param candidate - the streamed candidate to place.
+ * @param keep - the window bound.
+ * @returns true when an eviction happened (the level has candidates beyond the window).
+ */
+export function boundedInsert(window: ListingCandidate[], candidate: ListingCandidate, keep: number): boolean {
+  const at = window.findIndex(existing => candidate.name.localeCompare(existing.name) < 0)
+  if (at === -1) window.push(candidate)
+  else window.splice(at, 0, candidate)
+  if (window.length <= keep) return false
+  window.pop()
+  return true
+}
+
 /** Message text of an unknown thrown value. */
 function messageOf(error: unknown): string {
   /* v8 ignore next -- node:fs rejects with Error instances; the String arm only satisfies the unknown narrowing. */
@@ -127,25 +156,32 @@ export default class BrowseDirectoryPicker extends DirectoryPicker {
       throw new DirectoryPickerError('directory-unreadable', path, `cannot list "${path}": not a fully qualified path`)
     }
     const target = resolve(path ?? home)
-    let names: { name: string; isDirectory: boolean; isSymbolicLink: boolean }[]
+    // Stream the level (opendir, one dirent at a time) into a name-sorted
+    // window of maxEntries + 1 candidates: memory stays bounded no matter how
+    // many children the directory holds, the window keeps the name-sorted
+    // head, and the +1 slot lets an in-window extra row prove the cut. A
+    // window candidate that turns out non-enterable (broken symlink) is not
+    // backfilled from beyond the window — an eviction already marks the
+    // level truncated, which stays the honest answer.
+    const keep = this.config.maxEntries + 1
+    const window: ListingCandidate[] = []
+    let evicted = false
     try {
-      const dirents = await readdir(target, { withFileTypes: true })
-      names = dirents.map(dirent => ({
-        name: dirent.name,
-        isDirectory: dirent.isDirectory(),
-        isSymbolicLink: dirent.isSymbolicLink(),
-      }))
+      const level = await opendir(target)
+      for await (const dirent of level) {
+        // Only rows a browser could enter contend for the window; dirent
+        // says "directory" outright, a symlink needs the later stat probe.
+        if (!dirent.isDirectory() && !dirent.isSymbolicLink()) continue
+        const candidate = { name: dirent.name, isDirectory: dirent.isDirectory(), isSymbolicLink: dirent.isSymbolicLink() }
+        if (boundedInsert(window, candidate, keep)) evicted = true
+      }
     } catch (error: unknown) {
       throw new DirectoryPickerError('directory-unreadable', target, `cannot list ${target}: ${messageOf(error)}`)
     }
-    // Sort candidates before probing so the bound keeps the name-sorted head
-    // of the level and probing (symlink stat) stops with the bound instead of
-    // touching every child of an oversized directory.
-    names.sort((a, b) => a.name.localeCompare(b.name))
     const entries: DirectoryEntry[] = []
-    let truncated = false
-    for (const entry of names) {
-      const row = await directoryRow(target, entry.name, entry.isDirectory, entry.isSymbolicLink)
+    let truncated = evicted
+    for (const candidate of window) {
+      const row = await directoryRow(target, candidate.name, candidate.isDirectory, candidate.isSymbolicLink)
       if (row === null) continue
       if (entries.length === this.config.maxEntries) {
         truncated = true

packages/host/directory-picker-browse/tests/service.spec.ts

@@ -7,7 +7,8 @@ import { afterAll, beforeAll, describe, expect, it } from 'vitest'
 import { Context } from 'cordis'
 import { DirectoryPickerError } from '@deepseek-ai/dsh-host-directory-picker'
 import type { DirectoryPickerBrowseCapability } from '@deepseek-ai/dsh-host-directory-picker'
-import BrowseDirectoryPicker, { fullyQualified } from '../src/index.ts'
+import BrowseDirectoryPicker, { boundedInsert, fullyQualified } from '../src/index.ts'
+import type { ListingCandidate } from '../src/index.ts'
 
 let root: string
 let capability: DirectoryPickerBrowseCapability
@@ -21,6 +22,13 @@ beforeAll(async () => {
   await writeFile(join(root, 'notes.txt'), 'not a directory')
   await symlink(join(root, 'projects'), join(root, 'linked'), 'junction')
   await symlink(join(root, 'gone'), join(root, 'broken'), 'junction')
+  try {
+    await symlink(join(root, 'notes.txt'), join(root, 'file-link'))
+  } catch {
+    // Windows denies unprivileged file symlinks; the file-link row only
+    // feeds the POSIX lanes' coverage of the symlink-to-file arm, and every
+    // assertion below expects it to be filtered out anyway.
+  }
 
   const ctx = new Context()
   const fiber = ctx.plugin(BrowseDirectoryPicker)
@@ -63,11 +71,31 @@ describe('BrowseDirectoryPicker', () => {
       const exact = await bounded.list(join(root, 'projects'))
       expect(exact.entries.map(entry => entry.name)).toEqual(['harness'])
       expect(exact.truncated).toBe(false)
+      // A level that fits the window but exceeds the bound (two rows, bound
+      // one): the in-window extra row proves the cut without any eviction.
+      await mkdir(join(root, 'projects', 'harness', 'a'))
+      await mkdir(join(root, 'projects', 'harness', 'b'))
+      const inWindow = await bounded.list(join(root, 'projects', 'harness'))
+      expect(inWindow.entries.map(entry => entry.name)).toEqual(['a'])
+      expect(inWindow.truncated).toBe(true)
     } finally {
       await fiber.dispose()
     }
   })
 
+  it('boundedInsert keeps the window name-sorted and bounded, reporting evictions', () => {
+    const candidate = (name: string): ListingCandidate => ({ name, isDirectory: true, isSymbolicLink: false })
+    const window: ListingCandidate[] = []
+    expect(boundedInsert(window, candidate('m'), 2)).toBe(false)
+    expect(boundedInsert(window, candidate('z'), 2)).toBe(false)
+    // A smaller name lands in place and pushes the current largest out.
+    expect(boundedInsert(window, candidate('a'), 2)).toBe(true)
+    expect(window.map(entry => entry.name)).toEqual(['a', 'm'])
+    // A name beyond the window's tail enters last and leaves immediately.
+    expect(boundedInsert(window, candidate('t'), 2)).toBe(true)
+    expect(window.map(entry => entry.name)).toEqual(['a', 'm'])
+  })
+
   it('reports the ancestry as jump-target crumbs ending at the listed directory', async () => {
     const listing = await capability.list(join(root, 'projects'))
     const tail = listing.crumbs.at(-1)!