feat: balance layout and kbd workspace navigation

src/lib/layout-presets.test.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from "vitest";
 import {
   collectWindowIds,
   applyPresetToLayout,
+  balanceLayout,
   BUILT_IN_PRESETS,
 } from "./layout-presets";
 import type { MosaicNode } from "react-mosaic-component";
@@ -193,6 +194,84 @@ describe("layout-presets", () => {
     });
   });
 
+  describe("balanceLayout", () => {
+    it("returns null for null layout", () => {
+      expect(balanceLayout(null)).toBeNull();
+    });
+
+    it("returns single window unchanged", () => {
+      expect(balanceLayout("w1")).toBe("w1");
+    });
+
+    it("balances a simple binary split", () => {
+      const unbalanced: MosaicNode<string> = {
+        direction: "row",
+        first: "w1",
+        second: "w2",
+        splitPercentage: 70,
+      };
+      const balanced = balanceLayout(unbalanced);
+      expect(balanced).toEqual({
+        direction: "row",
+        first: "w1",
+        second: "w2",
+        splitPercentage: 50,
+      });
+    });
+
+    it("balances nested splits recursively", () => {
+      const unbalanced: MosaicNode<string> = {
+        direction: "row",
+        first: {
+          direction: "column",
+          first: "w1",
+          second: "w2",
+          splitPercentage: 30,
+        },
+        second: {
+          direction: "column",
+          first: "w3",
+          second: "w4",
+          splitPercentage: 80,
+        },
+        splitPercentage: 60,
+      };
+      const balanced = balanceLayout(unbalanced);
+
+      // All splits should be 50%
+      expect(balanced).toMatchObject({
+        splitPercentage: 50,
+        first: { splitPercentage: 50 },
+        second: { splitPercentage: 50 },
+      });
+    });
+
+    it("preserves window IDs and directions", () => {
+      const original: MosaicNode<string> = {
+        direction: "column",
+        first: "w1",
+        second: {
+          direction: "row",
+          first: "w2",
+          second: "w3",
+          splitPercentage: 75,
+        },
+        splitPercentage: 25,
+      };
+      const balanced = balanceLayout(original);
+      const windowIds = collectWindowIds(balanced);
+      expect(windowIds).toEqual(["w1", "w2", "w3"]);
+
+      // Check directions preserved
+      if (balanced && typeof balanced !== "string") {
+        expect(balanced.direction).toBe("column");
+        if (typeof balanced.second !== "string") {
+          expect(balanced.second.direction).toBe("row");
+        }
+      }
+    });
+  });
+
   describe("applyPresetToLayout", () => {
     it("throws error if too few windows", () => {
       const layout: MosaicNode<string> = "w1";

src/lib/layout-presets.ts

@@ -203,6 +203,31 @@ export function applyPresetToLayout(
   return preset.generate(windowIds);
 }
 
+/**
+ * Balances all split percentages in a layout tree to 50/50
+ * Useful for equalizing splits after manual resizing
+ */
+export function balanceLayout(
+  layout: MosaicNode<string> | null
+): MosaicNode<string> | null {
+  if (layout === null) {
+    return null;
+  }
+
+  // Leaf node (window ID), return as-is
+  if (typeof layout === "string") {
+    return layout;
+  }
+
+  // Branch node, balance this split and recurse
+  return {
+    direction: layout.direction,
+    first: balanceLayout(layout.first),
+    second: balanceLayout(layout.second),
+    splitPercentage: 50,
+  };
+}
+
 /**
  * Get a preset by ID
  */