fix(web): reject empty sidebar splits and clarify page targeting

.agents/notes/implemented/feature/2026-09-04-right-sidebar-docking-infrastructure.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 .agents/notes/implemented/feature/2026-09-04-right-sidebar-docking-infrastructure.md
-2026-09-04-right-sidebar-docking-infrastructure.md: 3f6bcff565598c4d8a24e374d308c388c1f6bb0a
-2026-09-04-right-sidebar-docking-infrastructure.zh.md: aea7aacc4cb50b8974ada4a7e7eec27ed41623b9
+2026-09-04-right-sidebar-docking-infrastructure.md: 936f73c9210baf4297eace2deb270bb9594d7e8d
+2026-09-04-right-sidebar-docking-infrastructure.zh.md: d234dbcbb2f60ba1dd3b3d9fca2936a16521751d

.agents/notes/implemented/feature/2026-09-04-right-sidebar-docking-infrastructure.md

@@ -39,7 +39,7 @@ The right Sidebar uses one mounted content tree in normal and fullscreen modes;
 
 [Default pages](2026-09-08-sidebar-default-pages.md) supersede default-guide reseeding here; [last-tab close rules](2026-09-08-sidebar-last-tab-close-rules.md) own explicit closing, while moving tabs still settles emptied panes.
 
-`ui-sidebar-right` keeps one `SurfaceState` per session id — the layout, its history, and the mint counter — in a store declared at the seat registration. Every action mints the ids its intent needs, asks a kit planner for the operations, runs the settle planner over the result, and records the whole intent as one history entry before assigning the session's surface back; no action edits a layout in place. The settle step is the product's rule: a docked pane whose last tab is closed, moved out, or floated is merged away, and when only the root pane remains and it is empty, the current default page is reseeded — there is always at least one tab and never an empty pane, so no pane-closing gesture exists. State is memory-only: a reload returns every session to the collapsed default, and switching sessions keeps each surface where it was. Layout is presentation state and never enters the session log.
+`ui-sidebar-right` keeps one `SurfaceState` per session id — the layout, its history, and the mint counter — in a store declared at the seat registration. Every action mints the ids its intent needs, asks a kit planner for the operations, runs the settle planner over the result, and records the whole intent as one history entry before assigning the session's surface back; no action edits a layout in place. The settle step is the product's rule: a docked pane whose last tab is closed, moved out, or floated is merged away, and an expanded empty root pane receives the current default page. A collapsed surface may remain empty until its next expansion; no separate pane-closing gesture exists. State is memory-only: a reload returns every session to the collapsed default, and switching sessions keeps each surface where it was. Layout is presentation state and never enters the session log.
 
 ### Beyond the surface
 
@@ -69,7 +69,7 @@ The surface renders tabs whose bodies it does not know: each tab carries a `kind
 
 **Undo and redo buttons on the panel header.** Shipped first, then removed: the sequence is an architectural fact, and stepping it is not a product action yet. The API stays reachable as `@internal` methods for tests and the future navigation controller.
 
-**Empty panes as a persistent state.** The first design allowed a pane to stay after its last tab left, with a placeholder. Rejected because nothing offered a way to close such a pane; every intent settles the surface so an emptied pane is merged away and an emptied root pane reseeds the current default page.
+**Empty panes as a persistent state.** The first design allowed a pane to stay after its last tab left, with a placeholder. Rejected because nothing offered a way to close such a pane; every intent settles the surface so an emptied side pane is merged away. An empty root receives the current default page only while the column is expanded.
 
 **Inline the kit through `packages/util` and the `INLINE_SAFE` list.** A build probe showed it works, but the util build chain has no CSS pipeline and the kit ships a stylesheet; the static-linked client package (the `ui-primitives` precedent) was chosen knowing that changing the kit means rebuilding the shell and reloading.
 
@@ -77,7 +77,7 @@ The surface renders tabs whose bodies it does not know: each tab carries a `kind
 
 - The docking surface itself no longer overflows its panel: `.surface` and `.pane` clamp to the column (`min-width: 0`, `overflow: hidden`), so a long unwrapped line scrolls inside the body and the strip's controls stay in view in every split.
 - Layout is undoable and per session, and it is memory-only; a reload starts every session collapsed. Undo is reachable only through `@internal` service methods; the product shows no history controls.
-- A pane cannot be left empty and the surface cannot be left tabless: closing, moving out, or floating a pane's last tab drops the pane, and emptying the last pane restores the current default page.
+- An expanded surface has no empty panes. Empty side panes merge away; an empty root receives the current default page only while expanded. New sessions and a collapsed surface whose last tab closed remain empty until expansion.
 - A pane holds at most one guide tab: a second one cannot be added, opened, duplicated, or moved in; the guide's uniqueness is per pane, so a split still seeds its new pane with a guide.
 - A pane may split only when each equal half can still hold what cannot shrink: the strip's fixed controls (its width minus the chip box and the fill, so the top-right pane's chrome counts on the half that hosts it) plus one chip at its minimum, measured in the component layer after every commit and on resize. Otherwise the split control stays, disabled with its own copy, the matching edge drop zones are withheld, and panes the user narrows keep their size; the product permits at most two horizontal panes, regardless of widening or divider movement.
 - The Sidebar panel never moves when the presentation switches, and its slide is the same in both presentations; the conversation is the only thing that animates on a switch. A hidden panel keeps its tabs mounted, so a preview survives a collapse.

.agents/notes/implemented/feature/2026-09-04-right-sidebar-docking-infrastructure.zh.md

@@ -39,7 +39,7 @@ Agent 产出的文件是最尖锐的案例。产出文件 chip 或 `read` 行的
 
 [默认页](2026-09-08-sidebar-default-pages.zh.md)取代此处的默认补入引导页；[最后一个 tab 的关闭规则](2026-09-08-sidebar-last-tab-close-rules.zh.md)负责显式关闭，移动 tab 仍会处理被清空的格。
 
-`ui-sidebar-right` 为每个会话 id 保存一份 `SurfaceState`——布局、历史与铸造计数——住在坑位注册时声明的 store 里。每个 action 先铸造意图所需的 id，向库的 planner 索取操作，对结果跑一遍 settle planner，把整个意图记为一条历史账，再把该会话的 surface 整体赋回；没有 action 就地改布局。settle 是产品规则：最后一个 tab 被关闭、拖走或悬浮出去的停靠 pane 会被合并掉；只剩根 pane 且为空时重新种上当前默认页——永远至少有一个 tab、永远没有空 pane，所以不存在"关闭 pane"手势。状态仅在内存：刷新使所有会话回到折叠默认态，切换会话时各 surface 保持原样。布局是呈现状态，永不进入会话日志。
+`ui-sidebar-right` 为每个会话 id 保存一份 `SurfaceState`——布局、历史与铸造计数——住在坑位注册时声明的 store 里。每个 action 先铸造意图所需的 id，向库的 planner 索取操作，对结果跑一遍 settle planner，把整个意图记为一条历史账，再把该会话的 surface 整体赋回；没有 action 就地改布局。settle 是产品规则：最后一个 tab 被关闭、拖走或悬浮出去的停靠 pane 会被合并掉；展开且为空的根 pane 会填入当前默认页。折叠的布局可以保持为空，直到下次展开；没有单独的关闭 pane 手势。状态仅在内存：刷新使所有会话回到折叠默认态，切换会话时各 surface 保持原样。布局是呈现状态，永不进入会话日志。
 
 ### 面之外
 
@@ -69,7 +69,7 @@ Agent 产出的文件是最尖锐的案例。产出文件 chip 或 `read` 行的
 
 **面板头部的 undo 与 redo 按钮。** 先上后撤：序列是架构事实，步进它现在还不是产品动作。API 以 `@internal` 方法保留给测试与将来的导航控制器。
 
-**空 pane 作为一种持久状态。** 第一版允许 pane 在最后一个 tab 离开后带占位留下。否决，因为没有任何方式关掉这样的 pane；每个意图都会整理 surface，被清空的 pane 合并掉，被清空的根 pane 重新种上当前默认页。
+**空 pane 作为一种持久状态。** 第一版允许 pane 在最后一个 tab 离开后带占位留下。否决，因为没有任何方式关掉这样的 pane；每个意图都会整理 surface，被清空的侧 pane 合并掉。空根 pane 只在该列展开时填入当前默认页。
 
 **经 `packages/util` 与 `INLINE_SAFE` 清单内联库。** 构建探针证明可行，但 util 构建链没有 CSS 管线而库带样式表；在知晓改库须重建壳并刷新页面的前提下，选择静态链接的 client 包（`ui-primitives` 先例）。
 
@@ -77,7 +77,7 @@ Agent 产出的文件是最尖锐的案例。产出文件 chip 或 `read` 行的
 
 - 停靠面自身不再溢出面板：`.surface` 与 `.pane` 收在列内（`min-width: 0`、`overflow: hidden`），长的不换行行在正文内滚动，tab 条控件在任何分栏下都可见。
 - 布局可撤销且按会话隔离，同时仅在内存；刷新使所有会话回到折叠态。undo 只能经 `@internal` 服务方法触达；产品不显示历史控件。
-- pane 不能留空、surface 不能没有 tab：关闭、拖走或悬浮出 pane 的最后一个 tab 会删掉该 pane，清空最后一个 pane 会恢复当前默认页。
+- 展开的布局不保留空 pane。空侧 pane 被合并，空根 pane 只在展开时填入当前默认页。新会话以及关闭最后一个 tab 后收起的布局保持为空，直到下次展开。
 - 一个 pane 最多持有一个引导 tab：第二个不能被添加、打开、复制或搬入；唯一性按 pane 算，所以分栏仍给新 pane 种引导。
 - pane 只有在等分后的两半都仍能容下不可收缩部分时才可分栏：tab 条的固定控件（条宽减去 chip 盒与填充，因此右上 pane 的面板控件只计在承载它的那一半）加一个最小宽度的 chip，由组件层在每次提交与尺寸变化后测量。否则分栏控件保留但禁用并带自己的文案，对应的边缘落区不再提供，用户拖窄的 pane 保持原尺寸；产品最多两个水平窗格，不因拉宽或拖分隔条而提高上限。
 - 切换呈现模式时 Sidebar 面板一动不动，两种模式的平移一模一样；切换时只有会话区在动。隐藏的面板保持 tab 挂载，预览在折叠后仍在。

.agents/notes/implemented/feature/2026-09-05-sidebar-text-preview-and-file-tree.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 .agents/notes/implemented/feature/2026-09-05-sidebar-text-preview-and-file-tree.md
-2026-09-05-sidebar-text-preview-and-file-tree.md: 1a743c35634c5772e8173b770228a7f736a9d710
-2026-09-05-sidebar-text-preview-and-file-tree.zh.md: 72253286862f1e8729683fb719e83cfcf544d8e8
+2026-09-05-sidebar-text-preview-and-file-tree.md: 9c0b6db832f19ba758ba2d3851db72f9a1fdb785
+2026-09-05-sidebar-text-preview-and-file-tree.zh.md: a5173c20b5203942df3c6f86b2bef5961946fa08

.agents/notes/implemented/feature/2026-09-05-sidebar-text-preview-and-file-tree.md

@@ -24,7 +24,7 @@ The body is a centred column — a lead line (`侧栏用来放你想一直看着
 
 The body is also the replacement seam. It renders the `sidebar.right.tab.guide` chain with the shipped guide as the chain's fallback, so a product that registers its own entry takes the whole body, and with no entry, or every entry declining, the shipped guide draws. Because the shipped guide is the fallback and not a chain entry, there is always exactly one body and it cannot be outvoted by accident.
 
-A pane holds at most one guide, and the docking layer enforces it as product behaviour: the strip's add control hides while a guide is present, opening the guide into such a pane focuses it, a guide is never duplicated, and a guide dragged, dropped, or docked into a pane that already has one merges into it (the arriving tab closes). Settling a surface reseeds the guide when the root pane empties, so there is always at least one tab and never an empty pane.
+A pane holds at most one guide, and the docking layer enforces it as product behaviour: the strip's add control hides while a guide is present, opening the guide into such a pane focuses it, a guide is never duplicated, and a guide dragged, dropped, or docked into a pane that already has one merges into it (the arriving tab closes). An expanded empty root receives the current default page. Collapsed layouts may remain empty until expansion, when the default-page selection runs.
 
 ### The text preview
 

.agents/notes/implemented/feature/2026-09-05-sidebar-text-preview-and-file-tree.zh.md

@@ -24,7 +24,7 @@ Sidebar 随包交付三个 tab 类型：**引导页**（`ui-sidebar-right`）、
 
 体同时也是替换接缝。它渲染 `sidebar.right.tab.guide` 链，并以随包交付的引导页作为链的 fallback，于是注册了自己入口的产品接管整个体，而没有入口、或每个入口都拒绝时，随包交付的引导页照常绘制。因为随包交付的引导页是 fallback 而不是链上的一个入口，所以永远恰有一个体，也不可能被意外投掉。
 
-一个 pane 最多持有一个引导页，停靠层把这条作为产品行为强制执行：有引导页时 tab 条的添加控件隐藏，往这样的 pane 打开引导页只是聚焦它，引导页永不复制，被拖拽、落下或回坞进已有引导页的 pane 的引导页并入它（来者关闭）。settle 一个 surface 时，根 pane 空了就重新播下引导页，于是永远至少有一个 tab、永远没有空 pane。
+一个 pane 最多持有一个引导页，停靠层把这条作为产品行为强制执行：有引导页时 tab 条的添加控件隐藏，往这样的 pane 打开引导页只是聚焦它，引导页永不复制，被拖拽、落下或回坞进已有引导页的 pane 的引导页并入它（来者关闭）。展开且为空的根 pane 会填入当前默认页。折叠的布局可以保持为空，展开时才选择并创建默认页。
 
 ### 文本预览
 

.agents/notes/implemented/feature/2026-09-08-sidebar-last-tab-close-rules.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 .agents/notes/implemented/feature/2026-09-08-sidebar-last-tab-close-rules.md
-2026-09-08-sidebar-last-tab-close-rules.md: 4fb0e54af1075dd595d18db4d74779a7cfd2656b
-2026-09-08-sidebar-last-tab-close-rules.zh.md: 87cadf0f15eecb0cadc2fb2dacc5695771fd66f7
+2026-09-08-sidebar-last-tab-close-rules.md: ed76b0ad0b8bbadcf5eace12a7da3bd38c733d0e
+2026-09-08-sidebar-last-tab-close-rules.zh.md: bcc54c0c39cc65434f21ef8f6f81a382b6eecdb7

.agents/notes/implemented/feature/2026-09-08-sidebar-last-tab-close-rules.md

@@ -10,7 +10,7 @@ The settle planner guarantees the docked surface is never empty: closing the las
 
 ## Decision
 
-The docked surface's last tab carries one rule, decided in the Sidebar store's `closeTab` and mirrored to the kit through a new `canCloseTab(tabId)` control-policy prop (joining `canSplit` and `canAddTab`): the guide standing as the only docked tab is unclosable — no chip close control, no menu close item, and a programmatic close records nothing; any other lone tab closes together with the column in one history entry, resets fullscreen to push mode, and lets the settle planner prepare the current default page for the next expansion. `soleDockedTab(state, tabId)` in [stores.ts](../../../../packages/client/ui-sidebar-right/src/client/stores.ts) names the condition; floating panels take no part in it. Per the packages rule "enforce a decision in the operation that makes it", the store's `closeTab` is the enforcement and `canCloseTab` only mirrors it into the chrome. This rule supersedes the close-protection part of [the default-page decision](2026-09-08-sidebar-default-pages.md); its selection rule remains active.
+The docked surface's last tab carries one rule, decided in the Sidebar store's `closeTab` and mirrored to the kit through a new `canCloseTab(tabId)` control-policy prop (joining `canSplit` and `canAddTab`): the guide standing as the only docked tab is unclosable — no chip close control, no menu close item, and a programmatic close records nothing; any other lone tab closes together with the column in one history entry, resets fullscreen to push mode, and leaves the layout empty until the next expansion seeds the then-current default page. `soleDockedTab(state, tabId)` in [stores.ts](../../../../packages/client/ui-sidebar-right/src/client/stores.ts) names the condition; floating panels take no part in it. Per the packages rule "enforce a decision in the operation that makes it", the store's `closeTab` is the enforcement and `canCloseTab` only mirrors it into the chrome. This rule supersedes the close-protection part of [the default-page decision](2026-09-08-sidebar-default-pages.md); its selection rule remains active.
 
 Two kit-side presentation rules complete it in [TabPanel.tsx](../../../../packages/client/ui-dockkit/src/components/TabPanel.tsx) and [TabMenu.tsx](../../../../packages/client/ui-dockkit/src/components/TabMenu.tsx): a pane's lone chip whose close is withheld draws quiet — no capsule, no hover fill — since there is nothing to select against and nothing to do to it; and a menu that would hold no item at all produces no visible popup, so a secondary press on such a chip shows nothing rather than an empty box.
 

.agents/notes/implemented/feature/2026-09-08-sidebar-last-tab-close-rules.zh.md

@@ -10,7 +10,7 @@ settle planner 保证停靠面永不为空：关掉最后一个 tab 会重新播
 
 ## 决定
 
-停靠面的最后一个 tab 带一条规则，由 Sidebar store 的 `closeTab` 决定，并经新的控制策略 prop `canCloseTab(tabId)`（与 `canSplit`、`canAddTab` 并列）镜像给套件：作为唯一停靠 tab 的引导页不可关闭——chip 上没有关闭控件，菜单里没有关闭项，编程式关闭什么都不记录；任何其它 tab 独自留下时，关闭会连同整列一起收起、把全屏重置为挤压模式并记为一条历史，于是 settle planner 为下次展开准备当前默认页。[stores.ts](../../../../packages/client/ui-sidebar-right/src/client/stores.ts) 里的 `soleDockedTab(state, tabId)` 命名这个条件；浮动面板不参与。按照 packages 规则「在做出决定的操作里执行它」，store 的 `closeTab` 是执行点，`canCloseTab` 只是把它镜像到界面。本规则取代[默认页决策](2026-09-08-sidebar-default-pages.zh.md)中的关闭保护部分；其默认页选择规则仍然有效。
+停靠面的最后一个 tab 带一条规则，由 Sidebar store 的 `closeTab` 决定，并经新的控制策略 prop `canCloseTab(tabId)`（与 `canSplit`、`canAddTab` 并列）镜像给套件：作为唯一停靠 tab 的引导页不可关闭——chip 上没有关闭控件，菜单里没有关闭项，编程式关闭什么都不记录；任何其它 tab 独自留下时，关闭会连同整列一起收起、把全屏重置为挤压模式并记为一条历史，布局保持为空，直到下次展开时创建当时的默认页。[stores.ts](../../../../packages/client/ui-sidebar-right/src/client/stores.ts) 里的 `soleDockedTab(state, tabId)` 命名这个条件；浮动面板不参与。按照 packages 规则「在做出决定的操作里执行它」，store 的 `closeTab` 是执行点，`canCloseTab` 只是把它镜像到界面。本规则取代[默认页决策](2026-09-08-sidebar-default-pages.zh.md)中的关闭保护部分；其默认页选择规则仍然有效。
 
 两条套件侧的呈现规则在 [TabPanel.tsx](../../../../packages/client/ui-dockkit/src/components/TabPanel.tsx) 与 [TabMenu.tsx](../../../../packages/client/ui-dockkit/src/components/TabMenu.tsx) 里补全它：某格仅剩的一个 chip 在关闭被收起时画成安静样式——没有胶囊底色，没有悬停填充——因为既没有别的 tab 可供选择，也没有任何可对它做的事；一个连一项都没有的菜单不会产生可见弹层，于是对这样的 chip 次键按下什么都不显示，而不是画一个空框。
 

.agents/notes/implemented/feature/2026-09-09-sidebar-and-preview-interaction-polish.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 .agents/notes/implemented/feature/2026-09-09-sidebar-and-preview-interaction-polish.md
-2026-09-09-sidebar-and-preview-interaction-polish.md: 63205125fc5833f643217d38fabc9cb897ab1f9c
-2026-09-09-sidebar-and-preview-interaction-polish.zh.md: bcfcbeb61cae71b45539393df20a9a6bfc00e3f0
+2026-09-09-sidebar-and-preview-interaction-polish.md: df0e768aa1aea913344c356d84c2a7d3386ccc6b
+2026-09-09-sidebar-and-preview-interaction-polish.zh.md: d3f8b00fd86ec12d867d48a917cd4a65cab18ba9

.agents/notes/implemented/feature/2026-09-09-sidebar-and-preview-interaction-polish.md

@@ -10,7 +10,7 @@ Five small interaction defects around the right Sidebar and the document preview
 
 ## Decision
 
-**Default pages seed lazily.** `createSurface` in [stores.ts](../../../../packages/client/ui-sidebar-right/src/client/stores.ts) mints a collapsed, empty surface; the store's `advance` passes the seed factory to `planSettle` only when the intent leaves the column expanded. The expansion that would first show an empty layout is what seeds the then-current default page, and closing the last closable tab collapses the column and leaves the layout empty until the next expansion. The [last-tab close rule](2026-09-08-sidebar-last-tab-close-rules.md) and [default-page selection](2026-09-08-sidebar-default-pages.md) stay as decided; only the seeding moment moved.
+**Default pages seed lazily.** `createSurface` in [stores.ts](../../../../packages/client/ui-sidebar-right/src/client/stores.ts) mints a collapsed, empty surface; the store's `advance` passes the seed factory to `planSettle` only when the intent leaves the column expanded. The expansion that would first show an empty layout is what seeds the then-current default page, and closing the last closable tab collapses the column and leaves the layout empty until the next expansion. The [last-tab close rule](2026-09-08-sidebar-last-tab-close-rules.md) and [default-page selection](2026-09-08-sidebar-default-pages.md) stay as decided; default pages are created on expansion. Splitting an empty pane is a no-op: it mints no tabs, records no history, and reports no new pane.
 
 **Page uniqueness is pane-scoped.** The guide-only merge generalized to every page kind (`pageKind`/`panePage`): opening a page focuses an existing tab only inside the pane the open targets, and a page dragged, dropped, or docked into a pane already showing that kind's page merges into the pane's own. Resource tabs keep the kit's surface-wide reveal.
 

.agents/notes/implemented/feature/2026-09-09-sidebar-and-preview-interaction-polish.zh.md

@@ -10,7 +10,7 @@ Status: implemented
 
 ## Decision
 
-**默认页惰性播种。**[stores.ts](../../../../packages/client/ui-sidebar-right/src/client/stores.ts) 的 `createSurface` 铸造一个折叠且为空的停靠面；store 的 `advance` 只在意图让列保持展开时才把种子工厂传给 `planSettle`。首次会展示空布局的那次展开播种彼时的默认页；关闭最后一个可关 tab 时收起整列，布局保持为空直到下次展开。[最后一个 tab 的关闭规则](2026-09-08-sidebar-last-tab-close-rules.zh.md)与[默认页选择](2026-09-08-sidebar-default-pages.zh.md)维持原决定；改变的只是播种时机。
+**默认页惰性播种。**[stores.ts](../../../../packages/client/ui-sidebar-right/src/client/stores.ts) 的 `createSurface` 铸造一个折叠且为空的停靠面；store 的 `advance` 只在意图让列保持展开时才把种子工厂传给 `planSettle`。首次会展示空布局的那次展开播种彼时的默认页；关闭最后一个可关 tab 时收起整列，布局保持为空直到下次展开。[最后一个 tab 的关闭规则](2026-09-08-sidebar-last-tab-close-rules.zh.md)与[默认页选择](2026-09-08-sidebar-default-pages.zh.md)维持原决定；默认页在展开时创建。对空分栏执行 split 不产生变化，不创建 tab，不记录历史，也不返回新分栏。
 
 **页唯一性以格为界。**只对引导页的合并规则推广到每种页 kind（`pageKind`/`panePage`）：打开一个页只在这次打开的目标格内聚焦既有 tab；把页拖入、放入或收回到已展示该 kind 页的格会并入该格自己的 tab。资源 tab 保留套件的全停靠面聚焦。
 

packages/client/ui-primitives/tests/atoms.client.spec.tsx

@@ -108,11 +108,14 @@ describe('Menu', () => {
     // the focus move it causes is the one signal left, and it closes.
     const iframe = document.createElement('iframe')
     document.body.appendChild(iframe)
-    iframe.focus()
-    expect(document.activeElement).toBe(iframe)
-    fireEvent.blur(window)
-    expect(onClose).toHaveBeenCalledTimes(1)
-    iframe.remove()
+    try {
+      iframe.focus()
+      expect(document.activeElement).toBe(iframe)
+      fireEvent.blur(window)
+      expect(onClose).toHaveBeenCalledTimes(1)
+    } finally {
+      iframe.remove()
+    }
   })
 
   it('selected item shows the trailing check; align=end, side=top, and className apply', () => {

packages/client/ui-sidebar-right/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/client/ui-sidebar-right/README.md
-README.md: 484667e6286e672b0541b0345e2ba02c21215aed
-README.zh.md: 521406868e3fe62240a838cfc2ea41b2c78e3134
+README.md: d0bf1b9a52aa93760d388f1677181d111faebb72
+README.zh.md: 087c55d1ae12d22173e2d2d2c1b5e164df58c774

packages/client/ui-sidebar-right/README.md

@@ -65,7 +65,7 @@ Carrying the mint counter in the surface is what makes a recorded sequence repla
 
 After every action the kit's settle planner keeps the expanded surface populated: a docked pane whose last tab was moved out or floated is merged away, and an emptied root pane receives the default page. A collapsed surface holds no such backfill — a session starts collapsed and empty, and a close that collapses the column leaves it empty — the expansion that would first show an empty layout is what seeds the default page. Explicit closing follows [the default-page and close rules](#the-guide). While expanded there is always at least one tab, and never an empty pane — so there is no separate "close pane" gesture.
 
-The docked surface's last tab carries one more rule, decided in the store's `closeTab` and mirrored to the kit through `canCloseTab`: the guide standing as the only docked tab draws no close control and no menu close item — its chip sits quiet, and with no extension item contributed a secondary press opens no menu — and a programmatic close of it records nothing; any other tab standing alone closes together with the column in one entry — the settle planner reseeds the current default page for the next expansion. Floating panels take no part in the rule: they render whether or not the column is expanded, and their tabs close freely.
+The docked surface's last tab carries one more rule, decided in the store's `closeTab` and mirrored to the kit through `canCloseTab`: the guide standing as the only docked tab draws no close control and no menu close item — its chip sits quiet, and with no extension item contributed a secondary press opens no menu — and a programmatic close of it records nothing; any other tab standing alone closes together with the column in one entry — the layout stays empty until the next expansion seeds its current default page. Floating panels take no part in the rule: they render whether or not the column is expanded, and their tabs close freely.
 
 State is memory-only. A reload returns every session to the collapsed default; switching sessions keeps each surface where it was.
 
@@ -84,7 +84,7 @@ Two more seats extend what is already there: `sidebar.right.tab.guide` (chain) r
 <a id="ctxsidebarright"></a>
 ## `ctx.sidebarRight`
 
-`openResource(address, options?)` and `openTab(kind, options?)` are the navigation controller, and every way into the column calls one of them: the conversation's file links and a tool row's line reference (`openResource(fileAddress, { params: { line } })`), the strip's add control and a guide entry box (`openTab`), a file tree's rows (`tab.actions.openResource`). A resource address is a `dsh-resource://<type>/…` URI; without `options.kind` the registry claims it (globs and `canOpen`, best band wins), with it that kind's type in force opens it. A page is named by kind; the tab is recorded under an address this package composes and nobody else spells (`contract/seed.ts`). Both run the same steps as one history entry: a tab already showing the same (kind, contentId) is focused unless `revealIfOpened: false` — a resource wherever it sits, a page only within the pane the open targets (the same page in another pane never draws the open away); otherwise a new tab lands in `options.replaceTab`'s pane and slot (closing that tab), else `options.paneId`, else the active docked pane; the panel expands, because content the user cannot see is not opened. Then the Tab domain records the navigation — `params` reach the body as `navigation.params`, with `revision` stepped — outside the layout history. `params` is typed by what is opened: a viewer for a resource type merges its entry into `SidebarRightResourceParamsMap` (the text preview declares `{ line?: number }`); a page type that takes parameters merges into `SidebarRightTabParamsMap` under its kind; values are JSON-shaped by convention, unchecked at run time. An address outside `dsh-resource://`, one no type claims, or a kind nothing registered throws: that is a wiring mistake, not a user error.
+`openResource(address, options?)` and `openTab(kind, options?)` are the navigation controller, and every way into the column calls one of them: the conversation's file links and a tool row's line reference (`openResource(fileAddress, { params: { line } })`), the strip's add control and a guide entry box (`openTab`), a file tree's rows (`tab.actions.openResource`). A resource address is a `dsh-resource://<type>/…` URI; without `options.kind` the registry claims it (globs and `canOpen`, best band wins), with it that kind's type in force opens it. A page is named by kind; the tab is recorded under an address this package composes and nobody else spells (`contract/seed.ts`). Both run the same steps as one history entry: a resource tab already showing the same (kind, contentId) is focused wherever it sits unless `revealIfOpened: false`; page tabs always deduplicate within the target pane, regardless of that option; otherwise a new tab lands in `options.replaceTab`'s pane and slot (closing that tab), else `options.paneId`, else the active docked pane; the panel expands, because content the user cannot see is not opened. Then the Tab domain records the navigation — `params` reach the body as `navigation.params`, with `revision` stepped — outside the layout history. `params` is typed by what is opened: a viewer for a resource type merges its entry into `SidebarRightResourceParamsMap` (the text preview declares `{ line?: number }`); a page type that takes parameters merges into `SidebarRightTabParamsMap` under its kind; values are JSON-shaped by convention, unchecked at run time. An address outside `dsh-resource://`, one no type claims, or a kind nothing registered throws: that is a wiring mistake, not a user error.
 
 `close(tabId)` closes a tab; `active()` reads the active tab. `isExpanded()` and `toggleExpanded()` read and drive the column's expansion; the presentation switch is the panel's own control and not part of this face. Layout operations, for callers that arrange the column programmatically, each recorded like the gesture it stands in for: `focus(tabId)` focuses a tab and its pane; `split(paneId?)` splits a docked pane (the active one by default) under the same pane budget and room rule as the strip's control and returns the new pane's id, or `undefined` — recording nothing — when it cannot; `float(tabId, rect?)` takes a docked tab out into a panel; `dock(paneId)` returns a floating panel to the active docked pane. A tab or pane that does not exist, or already is where the call would put it, is left alone. The face exposes operations only: no layout snapshot, no operation log, no lookup by address. `_undo()` / `_redo()` step the mounted surface's history; they are `@internal` — the sequence has no user-facing control, and these exist for tests. Commands need a mounted session surface; with none, they throw rather than write into a surface nobody draws.
 
@@ -98,7 +98,7 @@ The Tab domain retains navigation, an abort signal, and bound actions per (Sessi
 
 Default pages depend on the number of registered guide entries, not the number of tab types or open tabs. Exactly one entry opens its page directly (Files in the shipped composition); zero or multiple entries open the guide. Explicitly adding a guide still opens the guide, even with one entry. The sole docked guide is the only tab that cannot close; closing any other sole tab also collapses the column. The chip, context menu, and `close` API apply the same rule.
 
-The guide tab is one entry capsule (a glyph and a title, nothing else) per `guide` entry the registered types contributed, in `order`, centred in the body; the guide has no words of its own. Picking a capsule calls `tab.actions.openTab(entry.kind, { replaceTab: true })`, so the guide gives way to the page it opened. A pane holds at most one guide tab. The strip's add control is drawn only while its pane holds none and opens one there with `openTab('guide', { paneId, revealIfOpened: false })`, so a guide in another pane does not capture the click; opening the guide into a pane that already has one focuses it instead; a guide dragged, dropped, or docked into such a pane merges into it — the arriving guide closes and the pane's own is focused; `duplicateTab` on the guide records nothing. A split, an emptied root pane, and the pane a sole tab vacates by dropping on its own edge use the same default-page rule, one tab per new pane; the self-edge drop leaves the dragged tab focused. A plain `openTab('guide')` keeps the tree-wide reveal every open has. The product allows two horizontal panes, initially equal, with divider ratios limited to 20%–80%. Insufficient width blocks a new split; with two panes already present, a body drop moves the tab between panes instead of creating a third. At the two-pane limit, split controls are hidden; closing back to one pane restores them.
+The guide tab is one entry capsule (a glyph and a title, nothing else) per `guide` entry the registered types contributed, in `order`, centred in the body; the guide has no words of its own. Picking a capsule calls `tab.actions.openTab(entry.kind, { replaceTab: true })`, so the guide gives way to the page it opened. A pane holds at most one guide tab. The strip's add control is drawn only while its pane holds none and opens one there with `openTab('guide', { paneId, revealIfOpened: false })`, so a guide in another pane does not capture the click; opening the guide into a pane that already has one focuses it instead; a guide dragged, dropped, or docked into such a pane merges into it — the arriving guide closes and the pane's own is focused; `duplicateTab` on the guide records nothing. A split, an expanded empty root pane, and the pane a sole tab vacates by dropping on its own edge use the same default-page rule, one tab per new pane; the self-edge drop leaves the dragged tab focused. A plain `openTab('guide')` opens or focuses the guide only within the active or named pane. Splitting an empty pane does nothing and returns no new pane. The product allows two horizontal panes, initially equal, with divider ratios limited to 20%–80%. Insufficient width blocks a new split; with two panes already present, a body drop moves the tab between panes instead of creating a third. At the two-pane limit, split controls are hidden; closing back to one pane restores them.
 
 <a id="copy"></a>
 ## Copy

packages/client/ui-sidebar-right/README.zh.md

@@ -65,7 +65,7 @@ kind: "package-reference"
 
 每个动作之后，套件的 settle planner 保证展开的停靠面有内容：最后一个 tab 被搬走或浮出的停靠格会被并掉；根格被清空时填入默认页。折叠的停靠面没有这种回填——会话以折叠且为空的停靠面开始，收起整列的关闭也让它保持为空——首次会展示空布局的那次展开才播种默认页。显式关闭遵循[默认页与关闭规则](#the-guide)。展开期间永远至少有一个 tab，永远没有空格——因此没有单独的「关闭格」手势。
 
-停靠面的最后一个 tab 还多带一条规则，由 store 的 `closeTab` 决定并经 `canCloseTab` 镜像给套件：作为唯一停靠 tab 的引导页不画关闭控件也不画菜单里的关闭项——它的 chip 呈安静样式，在没有扩展条目时次键按下也不弹出菜单——对它的编程式关闭什么都不记录；任何其它 tab 独自留下时，点击关闭会连同整列一起收起，记为一条历史——settle planner 为下次展开重新播种当前默认页。浮动面板不参与这条规则：它们无论列是否展开都会渲染，其 tab 照常关闭。
+停靠面的最后一个 tab 还多带一条规则，由 store 的 `closeTab` 决定并经 `canCloseTab` 镜像给套件：作为唯一停靠 tab 的引导页不画关闭控件也不画菜单里的关闭项——它的 chip 呈安静样式，在没有扩展条目时次键按下也不弹出菜单——对它的编程式关闭什么都不记录；任何其它 tab 独自留下时，点击关闭会连同整列一起收起，记为一条历史，布局保持为空，直到下次展开时创建当时的默认页。浮动面板不参与这条规则：它们无论列是否展开都会渲染，其 tab 照常关闭。
 
 状态只在内存中。刷新会让每个会话回到折叠的默认态；切换会话则让每个停靠面留在原处。
 
@@ -84,7 +84,7 @@ tab 类型分两阶段注册，随包发布的引导类型走的正是别的包
 <a id="ctxsidebarright"></a>
 ## `ctx.sidebarRight`
 
-`openResource(address, options?)` 与 `openTab(kind, options?)` 是导航控制器，进入该列的每条路都调用其中之一：会话区的文件链接与工具行的行号引用（`openResource(fileAddress, { params: { line } })`），tab 条的添加控件与引导入口框（`openTab`），文件树的行（`tab.actions.openResource`）。资源地址是 `dsh-resource://<type>/…` URI；不带 `options.kind` 时由注册表认领（glob 与 `canOpen`，最高档胜出），带它时由该 kind 生效的类型打开。页按 kind 命名；tab 记录在本包拼出、别处无人书写的地址下（`contract/seed.ts`）。两者以同一组步骤作为一条历史运行：已展示同一 (kind, contentId) 的 tab 被聚焦，除非 `revealIfOpened: false`——资源不论在哪个格都算，页只在这次打开的目标格内算（另一格里的同一页不会把这次打开吸走）；否则新 tab 落到 `options.replaceTab` 所在的格与位置（并关掉那个 tab），再退而落到 `options.paneId`，再退而落到活跃停靠格；面板展开，因为用户看不到的内容不算打开。随后 Tab 域记录这次导航——`params` 以 `navigation.params` 抵达正文，`revision` 递增——不进布局历史。`params` 按所开之物定型：某资源类型的查看器把自己那项并入 `SidebarRightResourceParamsMap`（文本预览声明 `{ line?: number }`）；接受参数的页类型按其 kind 并入 `SidebarRightTabParamsMap`；值约定为 JSON 形状，运行时不校验。`dsh-resource://` 之外的地址、无人认领的地址、或未注册的 kind 都会 throw：那是接线错误，不是用户错误。
+`openResource(address, options?)` 与 `openTab(kind, options?)` 是导航控制器，进入该列的每条路都调用其中之一：会话区的文件链接与工具行的行号引用（`openResource(fileAddress, { params: { line } })`），tab 条的添加控件与引导入口框（`openTab`），文件树的行（`tab.actions.openResource`）。资源地址是 `dsh-resource://<type>/…` URI；不带 `options.kind` 时由注册表认领（glob 与 `canOpen`，最高档胜出），带它时由该 kind 生效的类型打开。页按 kind 命名；tab 记录在本包拼出、别处无人书写的地址下（`contract/seed.ts`）。两者以同一组步骤作为一条历史运行：已展示同一 (kind, contentId) 的资源 tab 被聚焦，不限所在分栏，除非 `revealIfOpened: false`；页 tab 始终只在目标分栏内去重，不受该选项影响；否则新 tab 落到 `options.replaceTab` 所在的格与位置（并关掉那个 tab），再退而落到 `options.paneId`，再退而落到活跃停靠格；面板展开，因为用户看不到的内容不算打开。随后 Tab 域记录这次导航——`params` 以 `navigation.params` 抵达正文，`revision` 递增——不进布局历史。`params` 按所开之物定型：某资源类型的查看器把自己那项并入 `SidebarRightResourceParamsMap`（文本预览声明 `{ line?: number }`）；接受参数的页类型按其 kind 并入 `SidebarRightTabParamsMap`；值约定为 JSON 形状，运行时不校验。`dsh-resource://` 之外的地址、无人认领的地址、或未注册的 kind 都会 throw：那是接线错误，不是用户错误。
 
 `close(tabId)` 关闭一个 tab；`active()` 读取活动 tab。`isExpanded()` 与 `toggleExpanded()` 读取并驱动该列的展开；形态切换是面板自己的控件，不属于这个接口。布局操作供以编程方式安排该列的调用方使用，每个都像它替代的手势一样被记录：`focus(tabId)` 聚焦一个 tab 及其格；`split(paneId?)` 在与 tab 条控件相同的格预算与空间规则下分栏一个停靠格（默认活跃格），返回新格的 id，做不到时返回 `undefined`——且不记录任何东西；`float(tabId, rect?)` 把停靠 tab 浮出为浮窗；`dock(paneId)` 把浮窗放回活跃停靠格。不存在的 tab 或格、或已处于调用目标状态的，都原样不动。该接口只暴露操作：没有布局快照、没有操作日志、没有按地址查找。`_undo()` / `_redo()` 步进已挂载停靠面的历史；它们是 `@internal`——序列没有面向用户的控件，这两个只为测试存在。命令需要一个已挂载的会话停靠面；没有时它们 throw，而不是写进一个没人绘制的面里。
 
@@ -98,7 +98,7 @@ Tab域按（Session，Tab id）保留导航、中止信号与绑定动作；私
 
 默认页取决于已注册的引导入口数，不取决于 tab 类型数或已打开的 tab 数。恰好一个入口时直接打开对应页面（随包组合中为 Files）；没有入口或有多个入口时打开引导页。即使只有一个入口，显式添加引导页仍会打开引导页。只有作为唯一停靠 tab 的引导页不可关闭；关闭其它任何唯一 tab 时会同时收起整列。chip、上下文菜单与 `close` API 使用同一规则。
 
-引导 tab 是各已注册类型贡献的每个 `guide` 条目一个入口胶囊（一个图标加一个标题，别无其他），按 `order` 排列并在正文中居中；引导页自己没有文字。选中一个胶囊会调用 `tab.actions.openTab(entry.kind, { replaceTab: true })`，于是引导页让位给它打开的页。一个格最多持有一个引导 tab。tab 条的添加控件只在该格没有引导 tab 时绘制，并以 `openTab('guide', { paneId, revealIfOpened: false })` 在该格打开一个，这样别的格里的引导页不会截走这次点击；把引导页开进已有引导页的格则改为聚焦它；把引导页拖入、放入或收回到这样的格会合并进去——来者关闭，该格自己的被聚焦；对引导页 `duplicateTab` 不记录任何东西。分栏、被清空的根格、以及唯一 tab 拖到本格边缘分屏后腾出的格使用相同的默认页规则，每个新格一个 tab；这种本格边缘拖放让被拖的 tab 保持聚焦。普通的 `openTab('guide')` 保留每次打开都有的整树聚焦。产品最多保留左右两格，默认均分，分隔条限定20%～80%。宽度不足以容纳两格时不允许新分栏；已有两格时，正文拖放用于跨格移动，不再创建第三格。达到两格上限时隐藏分栏控件；关闭回单格后恢复。
+引导 tab 是各已注册类型贡献的每个 `guide` 条目一个入口胶囊（一个图标加一个标题，别无其他），按 `order` 排列并在正文中居中；引导页自己没有文字。选中一个胶囊会调用 `tab.actions.openTab(entry.kind, { replaceTab: true })`，于是引导页让位给它打开的页。一个格最多持有一个引导 tab。tab 条的添加控件只在该格没有引导 tab 时绘制，并以 `openTab('guide', { paneId, revealIfOpened: false })` 在该格打开一个，这样别的格里的引导页不会截走这次点击；把引导页开进已有引导页的格则改为聚焦它；把引导页拖入、放入或收回到这样的格会合并进去——来者关闭，该格自己的被聚焦；对引导页 `duplicateTab` 不记录任何东西。分栏、展开且为空的根格、以及唯一 tab 拖到本格边缘分屏后腾出的格使用相同的默认页规则，每个新格一个 tab；这种本格边缘拖放让被拖的 tab 保持聚焦。普通的 `openTab('guide')` 只在活跃或指定分栏内打开或聚焦引导页。对空分栏执行 split 不产生变化，也不返回新分栏。产品最多保留左右两格，默认均分，分隔条限定20%～80%。宽度不足以容纳两格时不允许新分栏；已有两格时，正文拖放用于跨格移动，不再创建第三格。达到两格上限时隐藏分栏控件；关闭回单格后恢复。
 
 <a id="copy"></a>
 ## 文案

packages/client/ui-sidebar-right/src/client/contract/slots.ts

@@ -105,7 +105,7 @@ export interface SidebarRightTabNavigation {
 export interface SidebarRightTabPlacement {
   /** Land a new tab in this pane instead. */
   readonly paneId?: PaneId
-  /** Defaults to `true`: a tab already showing the same content is focused instead of a second one opening. */
+  /** Resource tabs reveal existing content by default; `false` permits duplicates. Pages always deduplicate within the target pane. */
   readonly revealIfOpened?: boolean
   /** `true` opens in this tab's place — its pane and strip slot — and closes this tab in the same step. */
   readonly replaceTab?: boolean

packages/client/ui-sidebar-right/src/client/service.ts

@@ -111,8 +111,8 @@ export interface SidebarRightPlacement {
   /** Take this tab's place — its pane and its strip slot — and close it in the same step. */
   readonly replaceTab?: TabId
   /**
-   * Defaults to `true`: a tab already showing the same (kind, contentId) is
-   * focused and handed `params`. `false` opens another tab regardless.
+   * Resource tabs reveal an existing (kind, contentId) by default; `false`
+   * permits duplicates. Pages always deduplicate within the target pane.
    */
   readonly revealIfOpened?: boolean
 }
@@ -184,7 +184,7 @@ export interface ISidebarRight {
    * splits.
    * @param paneId - the pane to split; defaults to the active docked pane.
    * @returns the new pane's id, or `undefined` when nothing was split: the pane
-   *   is missing or floating, the budget is spent, or two halves would not fit.
+   *   is missing, floating, or empty, the budget is spent, or two halves would not fit.
    */
   split(paneId?: PaneId): PaneId | undefined
   /**

packages/client/ui-sidebar-right/src/client/stores.ts

@@ -88,7 +88,7 @@ export interface OpenContentIntent {
   readonly paneId?: PaneId
   /** Take this tab's pane and slot, and close it in the same entry. */
   readonly replaceTab?: TabId
-  /** `false` opens another tab even when the identity is already shown; defaults to `true`. */
+  /** Resource tabs reveal an existing identity by default; `false` permits duplicates. Pages always deduplicate within the target pane. */
   readonly revealIfOpened?: boolean
 }
 
@@ -286,6 +286,7 @@ export function createSidebarRightStore(
       splitPane: (d, sessionId: string, paneId?: PaneId, settled?: (paneId: PaneId) => void) => {
         d.bySession = seat(d, sessionId, (s) => {
           const next = advance(s, (state, mint, makeTab) => dockPaneIds(state).length >= 2
+            || getPane(state, paneId ?? activeDockPaneId(state)).tabs.length === 0
             ? []
             : planSplitPane(state, mint, paneId, makeTab), seed)
           if (settled !== undefined && next !== s) {

packages/client/ui-sidebar-right/tests/service.client.spec.ts

@@ -201,7 +201,7 @@ describe('SidebarRightController — opening', () => {
     expect(Object.values(layout().tabs).filter(tab => tab.title === 'a.txt')).toHaveLength(2)
   })
 
-  it('reveals an open guide for a plain open, as for any address', () => {
+  it('focuses the existing guide in the target pane', () => {
     const { controller, instance, publish, layout, tabOf, expand } = harness()
     instance.actions.open(SESSION)
     expand()

packages/client/ui-sidebar-right/tests/stores.client.spec.ts

@@ -12,6 +12,7 @@ import { describe, expect, it, vi } from 'vitest'
 import type { LayoutState, PaneId, TabId } from '@deepseek-ai/dsh-client-ui-dockkit'
 import { dockPaneIds, findTabPane, getPane, getSplit } from '@deepseek-ai/dsh-client-ui-dockkit'
 import { createSidebarRightStore } from '../src/client/stores.ts'
+import { pageAddress } from '../src/client/contract/seed.ts'
 
 const SESSION = 's-test'
 
@@ -99,6 +100,47 @@ describe('createSidebarRightStore — the sequence', () => {
     expect(Object.values(layout().tabs)).toHaveLength(1)
   })
 
+  it.each([false, true])('does not split an empty collapsed pane after close=%s', (afterClose) => {
+    const { actions, layout, surface } = harness()
+    if (afterClose) {
+      actions.openContent(SESSION, { kind: 'text', contentId: 'file:a', title: 'a' }, () => {})
+      actions.closeTab(SESSION, Object.values(layout().tabs)[0]!.id)
+    }
+    const before = surface()
+    const settled = vi.fn()
+    actions.splitPane(SESSION, undefined, settled)
+    expect(surface()).toBe(before)
+    expect(settled).not.toHaveBeenCalled()
+    expect(layout().expanded).toBe(false)
+    expect(Object.keys(layout().tabs)).toHaveLength(0)
+  })
+
+  it.each(['guide', 'files'])('opens %s in the requested pane and merges a moved duplicate there', (kind) => {
+    const { actions, layout } = harness()
+    const address = pageAddress(kind)
+    actions.openContent(SESSION, { kind, contentId: address, title: kind }, () => {})
+    const first = Object.values(layout().tabs)[0]!
+    const firstPane = layout().activePaneId
+    actions.splitPane(SESSION)
+    const secondPane = layout().activePaneId
+    const seed = getPane(layout(), secondPane).tabs[0]!
+    actions.openContent(SESSION, { kind: 'text', contentId: 'file:b', title: 'b', replaceTab: seed }, () => {})
+    const opened = vi.fn<(tabId: TabId) => void>()
+    actions.openContent(SESSION, { kind, contentId: address, title: kind, paneId: secondPane }, opened)
+    const second = opened.mock.calls[0]![0]
+    expect(second).not.toBe(first.id)
+    expect(getPane(layout(), firstPane).tabs).toEqual([first.id])
+    expect(getPane(layout(), secondPane).activeTabId).toBe(second)
+    expect(layout().activePaneId).toBe(secondPane)
+    const held = vi.fn()
+    actions.openContent(SESSION, { kind, contentId: address, title: kind, paneId: secondPane, revealIfOpened: false }, held)
+    expect(held).toHaveBeenCalledWith(second)
+    actions.dropTab(SESSION, first.id, secondPane, 'center')
+    expect(layout().tabs[first.id]).toBeUndefined()
+    expect(getPane(layout(), secondPane).activeTabId).toBe(second)
+    expect(dockPaneIds(layout())).toEqual([secondPane])
+  })
+
   it('allows two docked panes and rejects further splits without recording', () => {
     const { actions, layout, entries, expand } = harness()
     expand()