fix(directory-picker-browse): keep the typed level in the last pane

Skipping the draft-following scan whenever ANY pane happened to list the
directory was the cheaper rule and the wrong one: erasing a segment left the
level being typed on the LEFT, with its own child pane still standing to its
right, so the two panes stopped reading as "where I am, and where I came
from".

The pane arity is now the invariant the editor maintains — the last pane lists
the level the path names, its parent sits beside it, and only a display root
lists alone. Only that last pane's own tail costs no scan; every other
directory part re-lands.

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: c0375331e0e82fd6864b2027e7e36e0c6cb9986a
-README.zh.md: 91d35de8821414c095db2a7834309864b5df0cd6
+README.md: 04d97adf71ae4a3ea8d89b24098f27cbdee20961
+README.zh.md: 603afaed7e4b4c77e699e009fc612e73c06d73aa

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

@@ -6,7 +6,7 @@ The **in-app browsing backend** of the [directory-picker seam](../directory-pick
 
 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); window insertion is binary with an O(1) full-window tail rejection, and `list` threads the caller's `AbortSignal` so a disconnect or timeout stops the scan instead of letting it outlive the caller. 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).
 
-**Dual-face package**: the browser half (`./client`) fills [ui-workspace's](../../client/ui-workspace/README.md) two directory-flow holes with the in-app **Select Workspace Directory** dialog (figma `Harness` 813-23126 family — Miller two-column view whose navigations land selection-anchored and quiet: the previous view keeps rendering while a crumb jump or a submitted path is scanned (a "Loading…" pill floats over it only once the scan outlives a 300ms silence window, never shifting the columns), then target and parent legs land as one two-pane frame with the target re-selected as its actual parent-level entry — so stepping back never collapses and no intermediate frame flashes (a parent leg outliving its 200ms wait bound lands the target alone and upgrades in place; a failed or truncated parent leg keeps the single-pane landing; the display root keeps the single wide level); breadcrumb with a click-to-edit path zone, advertised by the pencil glyph at the bar's right edge and lit on hover in the editor's own footprint, whose editor seeds a trailing separator and then keeps the panes under the draft: the final segment prefix-filters the level its directory part names (case-insensitively, over the listed — possibly truncated — rows only; a tail nobody matches releases the filter instead of emptying the pane), while a directory part no pane lists is scanned after a 250ms rest and lands like any other navigation — selection-anchored, two-pane away from the display root — so typing deeper descends and erasing segments walks back up, moving the Miller view without leaving the editor (a level a pane already shows needs no scan at all: the filter alone answers the draft) — a speculative scan is silent when it fails, and Enter still navigates by the exact text, owning the view until it lands; the editor cancels on Escape or when focus leaves the dialog card (window/tab switches and in-card focus moves keep the draft), and panes the draft walked to stay where the walk ended — the crumbs name that level and Open's fallback target follows them, so cancelling closes the editor rather than rewinding the walk; a fixed-label show-hidden footer toggle over the host's `hidden` flags, with a dot-led typed prefix revealing its matches and the current selection exempt from every filter; nested New-folder dialog), driving `host.listDirectory`/`host.createDirectory` and registering its own locale namespace (`directory-browser`, zh default / en). One cordis.yml row therefore composes both sides of the browse interaction; the client carries no capability-kind branching, and mounting a second flow package fails at load (the holes are `single` kind).
+**Dual-face package**: the browser half (`./client`) fills [ui-workspace's](../../client/ui-workspace/README.md) two directory-flow holes with the in-app **Select Workspace Directory** dialog (figma `Harness` 813-23126 family — Miller two-column view whose navigations land selection-anchored and quiet: the previous view keeps rendering while a crumb jump or a submitted path is scanned (a "Loading…" pill floats over it only once the scan outlives a 300ms silence window, never shifting the columns), then target and parent legs land as one two-pane frame with the target re-selected as its actual parent-level entry — so stepping back never collapses and no intermediate frame flashes (a parent leg outliving its 200ms wait bound lands the target alone and upgrades in place; a failed or truncated parent leg keeps the single-pane landing; the display root keeps the single wide level); breadcrumb with a click-to-edit path zone, advertised by the pencil glyph at the bar's right edge and lit on hover in the editor's own footprint, whose editor seeds a trailing separator and then keeps the panes under the draft: the final segment prefix-filters the level its directory part names (case-insensitively, over the listed — possibly truncated — rows only; a tail nobody matches releases the filter instead of emptying the pane), while any other directory part is scanned after a 250ms rest and lands like any other navigation — selection-anchored, two-pane away from the display root — so typing deeper descends and erasing segments walks back up, moving the Miller view without leaving the editor; the pane arity is the invariant, the last pane always listing the level the path names with its parent beside it (only that level's own tail costs no scan, and only a display root lists alone) — a speculative scan is silent when it fails, and Enter still navigates by the exact text, owning the view until it lands; the editor cancels on Escape or when focus leaves the dialog card (window/tab switches and in-card focus moves keep the draft), and panes the draft walked to stay where the walk ended — the crumbs name that level and Open's fallback target follows them, so cancelling closes the editor rather than rewinding the walk; a fixed-label show-hidden footer toggle over the host's `hidden` flags, with a dot-led typed prefix revealing its matches and the current selection exempt from every filter; nested New-folder dialog), driving `host.listDirectory`/`host.createDirectory` and registering its own locale namespace (`directory-browser`, zh default / en). One cordis.yml row therefore composes both sides of the browse interaction; the client carries no capability-kind branching, and mounting a second flow package fails at load (the holes are `single` kind).
 
 ## Model Experience
 

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

@@ -6,7 +6,7 @@
 
 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）；窗口插入为二分查找、满窗尾部单次比较即拒绝，且 `list` 透传调用方的 `AbortSignal`，断连或超时会停止扫描而不是让它在调用方离开后继续。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)。
 
-**双面包**：browser half（`./client`）以应用内 **选择工作区目录** 对话框（figma `Harness` 813-23126 家族——Miller 双列视图，其导航以选中项为锚、安静落地：扫描 crumb 跳转或提交的路径期间，先前视图持续渲染（"Loading…" 胶囊仅在扫描超出 300ms 静默窗口后才浮于其上，绝不挪动各列），随后目标与父层级两程以单个双栏帧落地，目标被重新选中为其在父层级中的实际条目——因此后退绝不塌缩，也没有中间帧闪现（父层级这一程超出其 200ms 等待上限时，目标单独落地，随后就地升级；父层级这一程失败或被截断时保持单栏落地；展示根保持单个宽层级）；带点击即编辑路径区的面包屑，该区由栏右端的铅笔图标点明、悬停时以编辑器自身的轮廓亮起，其编辑器预填尾随分隔符，随后让下方各栏跟随草稿：末段对其目录部分所指的层级做前缀过滤（不区分大小写，且仅作用于已列出、可能被截断的行；无一匹配的末段会解除过滤，而不是把该栏清空），而任何一栏都未列出的目录部分会在停顿 250ms 后被扫描，并像其他任何一次导航那样落地——以选中项为锚，在展示根之外即双栏——于是继续键入即下潜、删掉末段即上退，Miller 视图随之移动而不必离开编辑器（某一栏已经展示的层级则根本不需要扫描：过滤本身就答复了草稿）——推测性扫描失败时保持沉默，而 Enter 仍按确切文本导航，并在落地前独占视图；编辑器按 Escape 或焦点离开对话框卡片即取消（窗口／标签页切换与卡片内焦点移动保留草稿），而草稿走到的层级会留在原地——面包屑指明该层级、Open 的兜底目标随之而动，因此取消只是关闭编辑器，并不回退这段行走；基于宿主 `hidden` 标志、标签固定的"显示隐藏"footer 开关，键入以点开头的前缀会显出其匹配项，且当前选中项不受任何过滤影响；嵌套新建文件夹对话框）填入 [ui-workspace](../../client/ui-workspace/README.md) 的两个目录流洞，驱动 `host.listDirectory`／`host.createDirectory`，并注册自己的 locale 命名空间（`directory-browser`，zh 默认／en）。因此一行 cordis.yml 同时组合浏览交互的两侧；client 侧不含任何能力 kind 分支，挂载第二个流程包会在加载期失败（洞为 `single` kind）。
+**双面包**：browser half（`./client`）以应用内 **选择工作区目录** 对话框（figma `Harness` 813-23126 家族——Miller 双列视图，其导航以选中项为锚、安静落地：扫描 crumb 跳转或提交的路径期间，先前视图持续渲染（"Loading…" 胶囊仅在扫描超出 300ms 静默窗口后才浮于其上，绝不挪动各列），随后目标与父层级两程以单个双栏帧落地，目标被重新选中为其在父层级中的实际条目——因此后退绝不塌缩，也没有中间帧闪现（父层级这一程超出其 200ms 等待上限时，目标单独落地，随后就地升级；父层级这一程失败或被截断时保持单栏落地；展示根保持单个宽层级）；带点击即编辑路径区的面包屑，该区由栏右端的铅笔图标点明、悬停时以编辑器自身的轮廓亮起，其编辑器预填尾随分隔符，随后让下方各栏跟随草稿：末段对其目录部分所指的层级做前缀过滤（不区分大小写，且仅作用于已列出、可能被截断的行；无一匹配的末段会解除过滤，而不是把该栏清空），而其余任何目录部分都会在停顿 250ms 后被扫描，并像其他任何一次导航那样落地——以选中项为锚，在展示根之外即双栏——于是继续键入即下潜、删掉末段即上退，Miller 视图随之移动而不必离开编辑器；分栏个数是这里的不变量：最后一栏永远是路径所指的那一层，其上一层在它旁边（只有这一层自己的末段不触发扫描，也只有展示根会独占一栏）——推测性扫描失败时保持沉默，而 Enter 仍按确切文本导航，并在落地前独占视图；编辑器按 Escape 或焦点离开对话框卡片即取消（窗口／标签页切换与卡片内焦点移动保留草稿），而草稿走到的层级会留在原地——面包屑指明该层级、Open 的兜底目标随之而动，因此取消只是关闭编辑器，并不回退这段行走；基于宿主 `hidden` 标志、标签固定的"显示隐藏"footer 开关，键入以点开头的前缀会显出其匹配项，且当前选中项不受任何过滤影响；嵌套新建文件夹对话框）填入 [ui-workspace](../../client/ui-workspace/README.md) 的两个目录流洞，驱动 `host.listDirectory`／`host.createDirectory`，并注册自己的 locale 命名空间（`directory-browser`，zh 默认／en）。因此一行 cordis.yml 同时组合浏览交互的两侧；client 侧不含任何能力 kind 分支，挂载第二个流程包会在加载期失败（洞为 `single` kind）。
 
 ## 模型体验
 

packages/host/directory-picker-browse/src/client/DirectoryBrowser.tsx

@@ -23,13 +23,14 @@
  * separator, and keeps the panes under the draft: the final segment
  * prefix-filters the level its directory part names (a dot-led prefix also
  * reveals the hidden entries it names, and a prefix nobody matches releases
- * the filter), while a directory part no pane lists is scanned after a short
+ * the filter), while any other directory part is scanned after a short
  * debounce and lands like any other navigation — selection-anchored and
- * two-pane away from the display root — so typing deeper descends and
- * erasing segments walks back up, moving the Miller view without leaving the
- * editor. Panes the draft walked to stay put when the editor closes
- * (cancellation included): the crumbs name where the walk ended, and Open's
- * fallback target follows them.
+ * two-pane away from the display root. The pane arity holds throughout: the
+ * last pane is the level the path names and the one beside it is its parent,
+ * so typing deeper descends and erasing segments walks back up, moving the
+ * Miller view without leaving the editor. Panes the draft walked to stay put
+ * when the editor closes (cancellation included): the crumbs name where the
+ * walk ended, and Open's fallback target follows them.
  */
 import { useCallback, useEffect, useRef, useState } from 'react'
 import clsx from 'clsx'
@@ -151,12 +152,16 @@ function draftPrefixFor(listing: DirectoryListing, draft: string | null): string
 }
 
 /**
- * The directory a draft addresses that no rendered pane lists — the level the
- * editor must scan for the panes to keep following the typed path. Null when
- * a pane already lists it (the prefix filter alone answers the draft), when
- * no separator has been typed yet, and when no level is listed at all: the
- * platform separator is read off a listing, so the editor's
- * failed-home-listing recovery path types blind until Enter.
+ * The directory a draft addresses that the panes are not already presenting
+ * as the current level — what the editor must scan to keep the view under the
+ * typed path. The pane arity is the invariant this preserves: the LAST pane
+ * always lists the level the path names, with its parent beside it (a display
+ * root lists alone), so a draft naming any other level re-lands rather than
+ * leaving a deeper level standing to the right of the one being typed. Null
+ * when that level is already the last pane, when no separator has been typed
+ * yet, and when no level is listed at all: the platform separator is read off
+ * a listing, so the editor's failed-home-listing recovery path types blind
+ * until Enter.
  */
 function pendingPreviewDirectory(
   parent: DirectoryListing | null,
@@ -165,9 +170,8 @@ function pendingPreviewDirectory(
 ): string | null {
   if (parent === null) return null
   const directory = draftDirectory(parent, draft)
-  if (directory === null || directory === levelDirectory(parent)) return null
-  if (child !== null && directory === levelDirectory(child)) return null
-  return directory
+  if (directory === null) return null
+  return directory === levelDirectory(child ?? parent) ? null : directory
 }
 
 /**

packages/host/directory-picker-browse/tests/directory-browser.spec.tsx

@@ -707,11 +707,13 @@ describe('DirectoryBrowser', () => {
     fireEvent.change(input, { target: { value: `${DOCS}/zzz` } })
     expect(within(columns()[1]!).getByText('harness')).toBeTruthy()
     expect(within(columns()[0]!).getByText('Documents')).toBeTruthy()
-    // Erasing back into the parent's own path moves the filter to the LEFT
-    // pane and releases the right one — no scan, both levels are on screen.
+    // Erasing back into the parent's own path re-lands on it rather than
+    // filtering the LEFT pane: the level being typed is always the last pane,
+    // never a pane with a deeper level standing to its right. Home is the
+    // display root, so it lands alone.
     fireEvent.change(input, { target: { value: `${HOME}/zz` } })
-    expect(within(columns()[0]!).getAllByRole('listitem').map(item => item.textContent)).toEqual(['Documents'])
-    expect(within(columns()[1]!).getByText('harness')).toBeTruthy()
+    await waitFor(() => { expect(columns()).toHaveLength(1) })
+    expect(screen.getAllByRole('listitem').map(item => item.textContent)).toEqual(['Documents'])
   })
 
   it('follows the draft into a directory no pane lists, landing the two-pane Miller view', async () => {
@@ -740,6 +742,26 @@ describe('DirectoryBrowser', () => {
     expect(columns()).toHaveLength(2)
   })
 
+  it('keeps the typed level in the last pane, its parent beside it, as the draft walks', async () => {
+    const b = mount()
+    await waitFor(() => { expect(screen.getByRole('listitem')).toBeTruthy() })
+    fireEvent.click(screen.getByRole('button', { name: 'browser.editPath' }))
+    const input = screen.getByLabelText<HTMLInputElement>('browser.editPath')
+    // Two levels down: the typed level on the right, its parent on the left.
+    fireEvent.change(input, { target: { value: `${HARNESS}/` } })
+    await waitFor(() => { expect(within(columns()[0]!).getByText('harness')).toBeTruthy() })
+    expect(columns()).toHaveLength(2)
+    expect(within(columns()[1]!).queryAllByRole('listitem')).toHaveLength(0)
+    // Erasing back to the parent's own path re-lands on it: the level being
+    // typed moves BACK into the last pane instead of staying on the left with
+    // its own child pane still to the right.
+    fireEvent.change(input, { target: { value: `${DOCS}/ha` } })
+    await waitFor(() => { expect(within(columns()[0]!).getByText('Documents')).toBeTruthy() })
+    expect(columns()).toHaveLength(2)
+    expect(within(columns()[1]!).getAllByRole('listitem').map(item => item.textContent)).toEqual(['harness'])
+    expect(b.listDirectory).toHaveBeenCalledWith(`${DOCS}/`, expect.anything())
+  })
+
   it('walks the panes back up when erased segments leave the listed levels', async () => {
     const b = mount()
     await waitFor(() => { expect(screen.getByRole('listitem')).toBeTruthy() })