feat(editor): add resizable split groups

README.md

@@ -319,6 +319,8 @@ All keybindings are customizable via [`keybindings.json`](config/keybindings.jso
 
 Set [`keyboard.modifierKey`](docs-web/src/content/docs/reference/settings.md#keyboard) to `"control+super"` to also accept Super/Cmd for Ctrl shortcuts, or `"super"` to use Super/Cmd instead. The default is `"control"`. Binding definitions stay unchanged, and the terminal must forward the shortcuts.
 
+Use the editor tab bar’s **More** menu to split right or down (up to four groups), or close a split. Each new group starts with an independent, numbered untitled document; opening a file replaces the untouched placeholder. The command palette groups split actions under **Split:**, including **Split: Equalize Sizes**. Views of the same document share text and undo history, with independent cursors and scrolling. **Ctrl+K Left/Right/Up/Down** focuses the group in that direction; **F6** and **Shift+F6** cycle groups, the sidebar, and the panel. Closing the last tab removes its group; **Close Split** merges its remaining tabs into a neighbor.
+
 The full default keybinding list is in [`docs-web/src/content/docs/reference/keybindings.md`](docs-web/src/content/docs/reference/keybindings.md).
 
 ## Testing

config/keybindings.json

@@ -86,6 +86,10 @@
   { "key": "f6", "command": "focus.nextGroup" },
   { "key": "shift+f6", "command": "focus.prevGroup" },
   { "key": "ctrl+f6", "command": "terminal.toggleShortcutForwarding" },
+  { "key": "ctrl+k left", "command": "focus.editorLeft" },
+  { "key": "ctrl+k right", "command": "focus.editorRight" },
+  { "key": "ctrl+k up", "command": "focus.editorUp" },
+  { "key": "ctrl+k down", "command": "focus.editorDown" },
   { "key": "f10", "command": "menu.file" },
   { "key": "alt+f", "command": "menu.file" },
   { "key": "alt+e", "command": "menu.edit" },

config/settings.json

@@ -4,7 +4,8 @@
   "appearance": {
     "icons": "none",
     "scrollbarGlyphs": "blocks",
-    "pointerShapes": true
+    "pointerShapes": true,
+    "highlightActiveGroupBorder": true
   },
   "editor": {
     "autoClosing": {

docs-web/src/content/docs/guides/editor.md

@@ -11,6 +11,16 @@ On exit, the current text-file tab list replaces the remembered list for that wo
 
 Sessions are kept outside the project under the config directory's `sessions/` folder, with at most 128 tabs per session and 32 sessions. Sessions unused for 30 days are removed, and missing or non-regular files are skipped during restoration. **Session: Clear Saved Tabs** removes saved sessions without closing open files and pauses session saving until the next launch.
 
+## Split Editors
+
+Use the editor tab bar's **More** menu to choose **Split Right** (side by side) or **Split Down** (stacked). Repeat on a group to create up to four editor groups, including a grid. Each new group starts with an independent untitled document, numbered across the workspace. Opening a file replaces that untouched placeholder; once edited, the untitled document stays in its own tab.
+
+Views of the same document share text, undo history, and save state, with independent cursors, selections, and scrolling. Opening a file normally uses the active group, including when the same document is already open elsewhere. Split commands use the **Split:** prefix in the command palette; the More menu keeps only **Split Right**, **Split Down**, and **Close Split** for managing splits.
+
+Click a group or press **Ctrl+K Left/Right/Up/Down** to focus it. The active group’s border is highlighted by default; turn off **Highlight active split** in **Settings > Appearance > Window** to disable it. **F6** and **Shift+F6** cycle through editor groups, the sidebar, and the panel.
+
+Drag dividers alongside editor content to resize groups; side-by-side dividers leave the tab rows clear. **Split: Equalize Sizes** in the command palette balances their sizes again. Closing a group's last tab removes that group; **Close Split** merges its tabs into a neighboring group, keeping one view when both contain the same document.
+
 ## Syntax Highlighting
 
 TTT highlights code with [textmate-go](https://github.com/eugenioenko/textmate-go), a pure Go port of VS Code's TextMate engine built for ttt. It embeds TextMate grammars for 124 languages, detected from the file name, and colors constructs that span lines (block comments, template literals, docstrings, tags with attributes on several lines) correctly.
@@ -86,8 +96,8 @@ They have no default shortcut. Bind them in `keybindings.json`, for example:
 
 ```json
 [
-  { "key": "ctrl+k up", "command": "view.scrollUp" },
-  { "key": "ctrl+k down", "command": "view.scrollDown" }
+  { "key": "ctrl+k pgup", "command": "view.scrollUp" },
+  { "key": "ctrl+k pgdn", "command": "view.scrollDown" }
 ]
 ```
 

docs-web/src/content/docs/reference/keybindings.md

@@ -21,8 +21,12 @@ In-app shortcut labels use `Ctrl` in Control mode, `Mod` (Ctrl or Super) in Both
 | Ctrl+P | `command.palette` | Open command palette |
 | Ctrl+K P | `file.quickOpen` | Quick open file |
 | Escape | *(built-in)* | Dismiss overlay / collapse cursors / focus the editor |
-| F6 | `focus.nextGroup` | Focus next group (editor → sidebar → bottom panel → editor; hidden groups are skipped) |
-| Shift+F6 | `focus.prevGroup` | Focus previous group (reverse order) |
+| F6 | `focus.nextGroup` | Focus next editor group, sidebar, or panel |
+| Shift+F6 | `focus.prevGroup` | Focus previous group |
+| Ctrl+K Left | `focus.editorLeft` | Focus editor group left |
+| Ctrl+K Right | `focus.editorRight` | Focus editor group right |
+| Ctrl+K Up | `focus.editorUp` | Focus editor group up |
+| Ctrl+K Down | `focus.editorDown` | Focus editor group down |
 
 ## File
 

docs-web/src/content/docs/reference/settings.md

@@ -71,6 +71,7 @@ Lua plugin key hooks receive enabled Super/Cmd shortcuts as Ctrl shortcuts in `"
 | `appearance.overrides` | object | `{}` | Replace any UI glyph, keyed by icon name (see [Icon overrides](#icon-overrides)). An override wins over both the plain and Nerd Font glyph. |
 | `appearance.scrollbarGlyphs` | string | `"blocks"` | Glyphs that draw git change marks on the editor scrollbar: `"blocks"` uses the half and eighth blocks every font has, which place a mark exactly near the top or bottom of a cell and stretch one in the middle to the nearer edge; `"legacy"` adds the Symbols for Legacy Computing thin bars, which place every mark to the exact eighth of a cell. Kitty, Ghostty, WezTerm and foot draw those themselves; elsewhere the font needs them or the marks show as boxes. |
 | `appearance.pointerShapes` | bool | `true` | Change the mouse pointer shape (I-beam, hand, resize divider, dragging hand) via terminal OSC 22 sequences. Set to `false` for compatibility with terminals or multiplexers that do not support OSC 22 or if you prefer a static pointer. Mouse clicks, selection, scrolling, drag gestures, and mouse reporting remain enabled when false. |
+| `appearance.highlightActiveGroupBorder` | bool | `true` | Highlight the active editor group’s border when editors are split. Changes apply immediately. Also in **Settings > Appearance > Window**. |
 
 ## Icon overrides
 
@@ -450,7 +451,8 @@ When `editor.formatOnSave` is `true`, external formatters take priority over LSP
   "appearance": {
     "icons": "none",
     "scrollbarGlyphs": "blocks",
-    "pointerShapes": true
+    "pointerShapes": true,
+    "highlightActiveGroupBorder": true
   },
   "editor": {
     "tabSize": 4,

internal/app/app.go

@@ -66,7 +66,8 @@ type TerminalSpec struct {
 type App struct {
 	language        languageState
 	Root            *ui.Root
-	EditorGroup     *ui.EditorGroupWidget
+	EditorGroup     *ui.EditorGroupWidget // Follows activation so commands target the group receiving keys.
+	EditorSplit     *ui.EditorLayoutWidget
 	Sidebar         *ui.SidebarWidget
 	SplitPanel      *ui.SplitPanelWidget
 	ContentSplit    *ui.ContentSplitWidget
@@ -777,12 +778,7 @@ func (a *App) Init(screen *term.TcellScreen, renderer *render.Renderer, lspManag
 		screen.PostEvent(tcell.NewEventInterrupt(nil))
 	})
 	a.RefreshImageCellSize()
-	a.EditorGroup.TabBar.PostDragAutoScrollTick = func(generation uint64) {
-		screen.PostEvent(tcell.NewEventInterrupt(&ui.TabDragAutoScrollTick{Generation: generation}))
-	}
-	a.EditorGroup.Editor.PostDragAutoScrollTick = func(generation uint64) {
-		screen.PostEvent(tcell.NewEventInterrupt(&ui.EditorDragAutoScrollTick{Generation: generation}))
-	}
+	a.wireEditorAutoScroll(a.EditorGroup)
 	highlight.SetStepScheduler(func() {
 		screen.PostEvent(tcell.NewEventInterrupt(&highlightStep{}))
 	})
@@ -946,6 +942,7 @@ func openURLCommand(rawURL, platform string) *exec.Cmd {
 }
 
 func (a *App) FlushEditorOnChange() {
+	a.EditorGroup.SyncDocumentViews()
 	if a.EditorGroup.Editor != nil {
 		a.EditorGroup.Editor.FlushOnChange()
 	}

internal/app/app_lsp.go

@@ -640,7 +640,7 @@ func (a *App) applyInteractiveCodeActionEdit(path string, edit *lsp.WorkspaceEdi
 	for _, batch := range batches {
 		batchPath := URIToPath(batch.URI)
 		captured, wasOpen := openBuffers[batchPath]
-		current := a.EditorGroup.BufferForPath(batchPath)
+		current := a.editorBufferForPath(batchPath)
 		if (!wasOpen && current != nil) ||
 			(wasOpen && (current != captured.Buffer || current == nil || current.Version() != captured.Version)) {
 			return false, false
@@ -652,9 +652,11 @@ func (a *App) applyInteractiveCodeActionEdit(path string, edit *lsp.WorkspaceEdi
 
 func (a *App) snapshotCodeActionBuffers() map[string]codeActionBufferSnapshot {
 	snapshots := make(map[string]codeActionBufferSnapshot)
-	for _, path := range a.EditorGroup.OpenFilePaths() {
-		if buf := a.EditorGroup.BufferForPath(path); buf != nil {
-			snapshots[path] = codeActionBufferSnapshot{Buffer: buf, Version: buf.Version()}
+	for _, group := range a.editorGroups() {
+		for _, path := range group.OpenFilePaths() {
+			if buf := a.editorBufferForPath(path); buf != nil {
+				snapshots[path] = codeActionBufferSnapshot{Buffer: buf, Version: buf.Version()}
+			}
 		}
 	}
 	return snapshots

internal/app/callbacks.go

@@ -181,9 +181,14 @@ func (a *App) ShowChangesFolderContextMenu(dir, _ string, staged bool, sx, sy in
 
 func (a *App) DiffSearchSources() []ui.DiffSearchSource {
 	seen := map[string]bool{}
-	sources := a.EditorGroup.DiffTabSources()
-	for _, s := range sources {
-		seen[s.TabName] = true
+	var sources []ui.DiffSearchSource
+	for _, group := range append([]*ui.EditorGroupWidget{a.EditorGroup}, a.editorGroups()...) {
+		for _, source := range group.DiffTabSources() {
+			if !seen[source.TabName] {
+				seen[source.TabName] = true
+				sources = append(sources, source)
+			}
+		}
 	}
 	for _, g := range a.Changes.Groups() {
 		if !g.IsPR {
@@ -202,7 +207,7 @@ func (a *App) DiffSearchSources() []ui.DiffSearchSource {
 
 func (a *App) NavigateToSearchMatch(path string, line, col int) {
 	if strings.HasSuffix(path, " (diff)") {
-		if !a.EditorGroup.SwitchToTabByPath(path) {
+		if !a.switchToDiffTab(path) {
 			filePath := strings.TrimSuffix(path, " (diff)")
 			for _, g := range a.Changes.Groups() {
 				if !g.IsPR {
@@ -276,7 +281,7 @@ func joinReplacedLines(lines []string, original []byte) []byte {
 }
 
 func (a *App) ApplySearchReplace(filePath string, matches []ui.SearchMatch, replacement string, opts ui.SearchOptions) {
-	if a.EditorGroup.IsDirtyPath(filePath) {
+	if a.isEditorPathDirty(filePath) {
 		a.StatusWarn(i18n.Format("status.hasUnsavedChangesSaveItBeforeReplacing", i18n.Args{"filename": filepath.Base(filePath)}))
 		return
 	}
@@ -300,7 +305,7 @@ func (a *App) ApplySearchReplace(filePath string, matches []ui.SearchMatch, repl
 		return
 	}
 	a.invalidateRepositoryPath(filePath, RepositoryWorktree)
-	a.EditorGroup.ReloadFile(filePath)
+	a.reloadFile(filePath)
 	a.Search.Refresh()
 	a.StatusNotify(i18n.Format("status.replacedMatchesIn", i18n.Args{"matchesCount": len(matches), "filename": filepath.Base(filePath)}))
 }
@@ -332,7 +337,7 @@ func (a *App) confirmSearchReplaceAll(allMatches map[string][]ui.SearchMatch, re
 			replacedMatches, replacedFiles := 0, 0
 			var skipped []string
 			for filePath, matches := range allMatches {
-				if a.EditorGroup.IsDirtyPath(filePath) {
+				if a.isEditorPathDirty(filePath) {
 					skipped = append(skipped, filepath.Base(filePath))
 					continue
 				}
@@ -357,7 +362,7 @@ func (a *App) confirmSearchReplaceAll(allMatches map[string][]ui.SearchMatch, re
 				if invalidatePath == "" {
 					invalidatePath = filePath
 				}
-				a.EditorGroup.ReloadFile(filePath)
+				a.reloadFile(filePath)
 			}
 			a.invalidateRepositoryPath(invalidatePath, RepositoryWorktree)
 			a.Search.Refresh()
@@ -561,6 +566,7 @@ func (a *App) fetchPRFileContent(dv *ui.DiffEditorWidget, owner, repo, baseSHA,
 			fetchErr = err
 		}
 		a.Screen.PostEvent(tcell.NewEventInterrupt(&DiffContentResult{
+			Widget:   dv,
 			TabName:  tabName,
 			OldLines: oldLines,
 			NewLines: newLines,
@@ -730,16 +736,9 @@ func registerWidgetCallbacks(app *App) {
 		app.Root.SetFocus(app.EditorGroup)
 	}
 
-	app.EditorGroup.OnActiveTabChange = func() {
-		app.Root.ClearEditorLinkHover()
-		if findBar, ok := app.Root.TopOverlayWidget().(*ui.FindBarWidget); ok && findBar.OnEditorTabChange != nil {
-			findBar.OnEditorTabChange()
-		}
-		if bar := app.findBar(); bar != nil && bar.Query() != "" {
-			return
-		}
-		app.applySearchHighlights()
-	}
+	app.wireEditorGroupActivation(app.EditorGroup)
+
+	app.EditorGroup.OnActiveTabChange = app.editorTabChanged
 
 	app.EditorGroup.TabBar.OnTabClose = func(index int) {
 		app.EditorGroup.SwitchTab(index)
@@ -786,11 +785,6 @@ func registerWidgetCallbacks(app *App) {
 	}
 
 	app.Explorer.OnAction = func(id string) { reg.Execute(id) }
-	app.EditorGroup.OnEmpty = func() {
-		if app.welcomeWhenEmpty && len(app.Workspace.Paths()) == 0 {
-			app.ShowEmptyState()
-		}
-	}
 	app.Explorer.OnOpenFile = func(path string) {
 		app.EditorGroup.OpenFile(path)
 		app.FocusEditorIfEnabled()
@@ -888,12 +882,7 @@ func registerWidgetCallbacks(app *App) {
 	app.ContentSplit.OnResize = app.resizePanel
 	app.ContentSplit.OnResizeEnd = app.finishPanelResize
 
-	app.ContentSplit.OnTopClick = func() {
-		if app.Root.HasModalOverlay() || app.Root.FocusClaimed() {
-			return
-		}
-		app.Root.SetFocus(app.EditorGroup)
-	}
+	app.ContentSplit.OnTopClick = app.focusEditorAfterClick
 
 	app.ContentSplit.OnBottomClick = func() {
 		if app.Root.HasModalOverlay() || app.Root.FocusClaimed() {
@@ -970,10 +959,36 @@ func registerWidgetCallbacks(app *App) {
 }
 
 func (a *App) tabMoreMenu() []ui.ContextMenuItem {
-	return []ui.ContextMenuItem{
+	items := []ui.ContextMenuItem{
 		{Label: i18n.Text("menu.reopenClosedTab"), Shortcut: a.KeyFor("tab.reopenClosed"), Command: "tab.reopenClosed", Disabled: !a.EditorGroup.HasClosedTabs()},
 		ui.MenuSep(),
 		{Label: i18n.Text("menu.closeAll"), Command: "tab.closeAll"},
 		{Label: i18n.Text("menu.closeAllSaved"), Command: "tab.closeAllSaved"},
+		ui.MenuSep(),
+	}
+	return append(items, a.editorGroupMenu()...)
+}
+
+func (app *App) editorTabChanged() {
+	app.Root.ClearEditorLinkHover()
+	if findBar, ok := app.Root.TopOverlayWidget().(*ui.FindBarWidget); ok && findBar.OnEditorTabChange != nil {
+		findBar.OnEditorTabChange()
+	}
+	if bar := app.findBar(); bar != nil && bar.Query() != "" {
+		return
+	}
+	app.applySearchHighlights()
+}
+
+func (a *App) switchToDiffTab(path string) bool {
+	if a.EditorGroup.SwitchToTabByPath(path) {
+		return true
 	}
+	for _, group := range a.editorGroups() {
+		if group.DiffWidgetByTab(path) != nil {
+			a.activateEditorGroup(group)
+			return group.SwitchToTabByPath(path)
+		}
+	}
+	return false
 }

internal/app/changes_async.go

@@ -563,10 +563,13 @@ func readCommitDetail(ctx context.Context, incarnation uint64, source repository
 func (a *App) OpenCommitDetail(dir, ref, short string) {
 	a.cancelPendingDiff()
 	tabID := commitDetailTabID(dir, ref)
-	if a.EditorGroup.CommitDetailWidgetByTab(tabID) != nil {
-		a.EditorGroup.SwitchToTabByPath(tabID)
-		a.FocusEditorIfEnabled()
-		return
+	for _, group := range a.editorGroups() {
+		if group.CommitDetailWidgetByTab(tabID) != nil {
+			a.activateEditorGroup(group)
+			group.SwitchToTabByPath(tabID)
+			a.FocusEditorIfEnabled()
+			return
+		}
 	}
 
 	source := a.Repository.repositorySource(dir)
@@ -636,14 +639,24 @@ func (a *App) ShutdownGitReads() {
 	}
 }
 
+func (a *App) commitDetailForResult(tabID, dir, ref string, incarnation uint64) *ui.CommitDetailWidget {
+	for _, group := range a.editorGroups() {
+		detail := group.CommitDetailWidgetByTab(tabID)
+		if detail != nil && detail.Dir == dir && detail.Ref == ref && detail.Incarnation == incarnation {
+			return detail
+		}
+	}
+	return nil
+}
+
 // ApplyCommitDetail fills only the still-open incarnation whose repository and
 // full hash match the result. Closing the tab while Git runs supersedes it.
 func (a *App) ApplyCommitDetail(result *CommitDetailResult) {
 	if result == nil || result.Canceled {
 		return
 	}
-	detail := a.EditorGroup.CommitDetailWidgetByTab(commitDetailTabID(result.Dir, result.Ref))
-	if detail == nil || detail.Dir != result.Dir || detail.Ref != result.Ref || detail.Incarnation != result.Incarnation {
+	detail := a.commitDetailForResult(commitDetailTabID(result.Dir, result.Ref), result.Dir, result.Ref, result.Incarnation)
+	if detail == nil {
 		return
 	}
 	if !result.AuthoredAt.IsZero() {