feat: add opt-in split buttons to block headers (#3159)

Add two icon buttons (horizontal/vertical split) to every block's header
bar, gated behind a new `app:showsplitbuttons` setting (default false).
When enabled, the buttons appear before the settings cog.

Motivation: for users who split panes frequently, having the buttons
always visible speeds up the workflow vs. right-click > context menu.
The split functionality already exists — this just surfaces it more
conveniently.

- New setting `app:showsplitbuttons` (Go + TS + default config)
- Split buttons in `blockframe-header.tsx`, using existing
`createBlockSplitHorizontally`/`createBlockSplitVertically`
- New pane clones the current block's meta so terminals inherit
shell/connection config

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: lucyfarnik

frontend/app/block/blockenv.ts

@@ -13,6 +13,7 @@ export type BlockEnv = WaveEnvSubset<{
     getSettingsKeyAtom: SettingsKeyAtomFnType<
         | "app:focusfollowscursor"
         | "app:showoverlayblocknums"
+        | "term:showsplitbuttons"
         | "window:magnifiedblockblurprimarypx"
         | "window:magnifiedblockopacity"
     >;

frontend/app/block/blockframe-header.tsx

@@ -11,7 +11,13 @@ import {
 import { ConnectionButton } from "@/app/block/connectionbutton";
 import { DurableSessionFlyover } from "@/app/block/durable-session-flyover";
 import { getBlockBadgeAtom } from "@/app/store/badge";
-import { recordTEvent, refocusNode } from "@/app/store/global";
+import {
+    createBlockSplitHorizontally,
+    createBlockSplitVertically,
+    recordTEvent,
+    refocusNode,
+    WOS,
+} from "@/app/store/global";
 import { globalStore } from "@/app/store/jotaiStore";
 import { uxCloseBlock } from "@/app/store/keymodel";
 import { TabRpcClient } from "@/app/store/wshrpcutil";
@@ -119,12 +125,45 @@ const HeaderEndIcons = React.memo(({ viewModel, nodeModel, blockId }: HeaderEndI
     const ephemeral = jotai.useAtomValue(nodeModel.isEphemeral);
     const numLeafs = jotai.useAtomValue(nodeModel.numLeafs);
     const magnifyDisabled = numLeafs <= 1;
+    const showSplitButtons = jotai.useAtomValue(blockEnv.getSettingsKeyAtom("term:showsplitbuttons"));
 
     const endIconsElem: React.ReactElement[] = [];
 
     if (endIconButtons && endIconButtons.length > 0) {
         endIconsElem.push(...endIconButtons.map((button, idx) => <IconButton key={idx} decl={button} />));
     }
+    if (showSplitButtons && viewModel?.viewType === "term") {
+        const splitHorizontalDecl: IconButtonDecl = {
+            elemtype: "iconbutton",
+            icon: "columns",
+            title: "Split Horizontally",
+            click: (e) => {
+                e.stopPropagation();
+                const blockAtom = WOS.getWaveObjectAtom<Block>(WOS.makeORef("block", blockId));
+                const blockData = globalStore.get(blockAtom);
+                const blockDef: BlockDef = {
+                    meta: blockData?.meta || { view: "term", controller: "shell" },
+                };
+                createBlockSplitHorizontally(blockDef, blockId, "after");
+            },
+        };
+        const splitVerticalDecl: IconButtonDecl = {
+            elemtype: "iconbutton",
+            icon: "grip-lines",
+            title: "Split Vertically",
+            click: (e) => {
+                e.stopPropagation();
+                const blockAtom = WOS.getWaveObjectAtom<Block>(WOS.makeORef("block", blockId));
+                const blockData = globalStore.get(blockAtom);
+                const blockDef: BlockDef = {
+                    meta: blockData?.meta || { view: "term", controller: "shell" },
+                };
+                createBlockSplitVertically(blockDef, blockId, "after");
+            },
+        };
+        endIconsElem.push(<IconButton key="split-horizontal" decl={splitHorizontalDecl} />);
+        endIconsElem.push(<IconButton key="split-vertical" decl={splitVerticalDecl} />);
+    }
     const settingsDecl: IconButtonDecl = {
         elemtype: "iconbutton",
         icon: "cog",

frontend/types/gotypes.d.ts

@@ -1422,6 +1422,7 @@ declare global {
         "term:bellindicator"?: boolean;
         "term:osc52"?: string;
         "term:durable"?: boolean;
+        "term:showsplitbuttons"?: boolean;
         "editor:minimapenabled"?: boolean;
         "editor:stickyscrollenabled"?: boolean;
         "editor:wordwrap"?: boolean;

pkg/wconfig/defaultconfig/settings.json

@@ -7,6 +7,7 @@
     "app:tabbar": "top",
     "app:confirmquit": true,
     "app:hideaibutton": false,
+    "term:showsplitbuttons": false,
     "app:disablectrlshiftarrows": false,
     "app:disablectrlshiftdisplay": false,
     "app:focusfollowscursor": "off",

pkg/wconfig/metaconsts.go

@@ -59,6 +59,7 @@ const (
 	ConfigKey_TermBellIndicator              = "term:bellindicator"
 	ConfigKey_TermOsc52                      = "term:osc52"
 	ConfigKey_TermDurable                    = "term:durable"
+	ConfigKey_TermShowSplitButtons           = "term:showsplitbuttons"
 
 	ConfigKey_EditorMinimapEnabled           = "editor:minimapenabled"
 	ConfigKey_EditorStickyScrollEnabled      = "editor:stickyscrollenabled"

pkg/wconfig/settingsconfig.go

@@ -110,6 +110,7 @@ type SettingsType struct {
 	TermBellIndicator       *bool    `json:"term:bellindicator,omitempty"`
 	TermOsc52               string   `json:"term:osc52,omitempty" jsonschema:"enum=focus,enum=always"`
 	TermDurable             *bool    `json:"term:durable,omitempty"`
+	TermShowSplitButtons    bool     `json:"term:showsplitbuttons,omitempty"`
 
 	EditorMinimapEnabled      bool    `json:"editor:minimapenabled,omitempty"`
 	EditorStickyScrollEnabled bool    `json:"editor:stickyscrollenabled,omitempty"`

schema/settings.json

@@ -168,6 +168,9 @@
         "term:durable": {
           "type": "boolean"
         },
+        "term:showsplitbuttons": {
+          "type": "boolean"
+        },
         "editor:minimapenabled": {
           "type": "boolean"
         },