diff --git a/src/features/team-mode/team-layout-tmux/rebalance-team-window.test.ts b/src/features/team-mode/team-layout-tmux/rebalance-team-window.test.ts
new file mode 100644
index 000000000..d392b6c15
--- /dev/null
+++ b/src/features/team-mode/team-layout-tmux/rebalance-team-window.test.ts
@@ -0,0 +1,84 @@
+/// <reference types="bun-types" />
+
+import { beforeEach, describe, expect, it, mock } from "bun:test"
+
+import {
+  rebalanceTeamWindowWith,
+  type RebalanceTeamWindowDeps,
+} from "./rebalance-team-window"
+
+describe("rebalanceTeamWindowWith", () => {
+  let runTmux: RebalanceTeamWindowDeps["runTmux"]
+  let log: RebalanceTeamWindowDeps["log"]
+  let calls: Array<Array<string>>
+
+  beforeEach(() => {
+    calls = []
+    runTmux = mock(async (args: string[]): Promise<{ success: boolean }> => {
+      calls.push(args)
+      return { success: true }
+    })
+    log = mock((): void => undefined)
+  })
+
+  it("#given main-vertical #when rebalance #then select-layout, set main-pane-width 60%, re-select-layout", async () => {
+    // given
+    const deps: RebalanceTeamWindowDeps = { runTmux, log }
+
+    // when
+    const result = await rebalanceTeamWindowWith("@1", "main-vertical", deps)
+
+    // then
+    expect(result).toBe(true)
+    expect(calls).toEqual([
+      ["select-layout", "-t", "@1", "main-vertical"],
+      ["set-window-option", "-t", "@1", "main-pane-width", "60%"],
+      ["select-layout", "-t", "@1", "main-vertical"],
+    ])
+  })
+
+  it("#given focus windowId and pane-list shrunk from 3 to 2 #when rebalanceTeamWindow runs #then select-layout is invoked with main-vertical", async () => {
+    // given
+    const deps: RebalanceTeamWindowDeps = { runTmux, log }
+
+    // when
+    const result = await rebalanceTeamWindowWith("@focus", "main-vertical", deps)
+
+    // then
+    expect(result).toBe(true)
+    expect(calls).toEqual([
+      ["select-layout", "-t", "@focus", "main-vertical"],
+      ["set-window-option", "-t", "@focus", "main-pane-width", "60%"],
+      ["select-layout", "-t", "@focus", "main-vertical"],
+    ])
+  })
+
+  it("#given tiled #when rebalance #then only select-layout called", async () => {
+    // given
+    const deps: RebalanceTeamWindowDeps = { runTmux, log }
+
+    // when
+    const result = await rebalanceTeamWindowWith("@1", "tiled", deps)
+
+    // then
+    expect(result).toBe(true)
+    expect(calls).toEqual([["select-layout", "-t", "@1", "tiled"]])
+  })
+
+  it("#given select-layout fails #when rebalance #then returns false, log once", async () => {
+    // given
+    runTmux = mock(async (args: string[]): Promise<{ success: boolean }> => {
+      calls.push(args)
+      return { success: false }
+    })
+
+    const deps: RebalanceTeamWindowDeps = { runTmux, log }
+
+    // when
+    const result = await rebalanceTeamWindowWith("@1", "main-vertical", deps)
+
+    // then
+    expect(result).toBe(false)
+    expect(log).toHaveBeenCalledTimes(1)
+  })
+})
diff --git a/src/features/team-mode/team-layout-tmux/rebalance-team-window.ts b/src/features/team-mode/team-layout-tmux/rebalance-team-window.ts
new file mode 100644
index 000000000..23abd0716
--- /dev/null
+++ b/src/features/team-mode/team-layout-tmux/rebalance-team-window.ts
@@ -0,0 +1,70 @@
+export type RebalanceLayout = "main-vertical" | "tiled"
+
+export type RebalanceTeamWindowDeps = {
+  runTmux: (args: string[]) => Promise<{ success: boolean }>
+  log: (message: string, meta?: Record<string, unknown>) => void
+}
+
+export async function rebalanceTeamWindowWith(
+  windowId: string,
+  layout: RebalanceLayout,
+  deps: RebalanceTeamWindowDeps,
+): Promise<boolean> {
+  if (windowId.length === 0) {
+    return false
+  }
+
+  const selectLayoutArgs = ["select-layout", "-t", windowId, layout]
+  const initialLayout = await deps.runTmux(selectLayoutArgs)
+  if (!initialLayout.success) {
+    deps.log("[rebalanceTeamWindow] FAILED", { windowId, layout, step: "select-layout" })
+    return false
+  }
+
+  if (layout === "tiled") {
+    return true
+  }
+
+  const setMainPaneWidth = await deps.runTmux([
+    "set-window-option",
+    "-t",
+    windowId,
+    "main-pane-width",
+    "60%",
+  ])
+  if (!setMainPaneWidth.success) {
+    deps.log("[rebalanceTeamWindow] FAILED", { windowId, layout, step: "set-window-option" })
+    return false
+  }
+
+  // tmux applies main-pane-width against the active layout, so select-layout again after resizing.
+  const finalLayout = await deps.runTmux(selectLayoutArgs)
+  if (!finalLayout.success) {
+    deps.log("[rebalanceTeamWindow] FAILED", { windowId, layout, step: "select-layout" })
+    return false
+  }
+
+  return true
+}
+
+export async function rebalanceTeamWindow(
+  windowId: string,
+  layout: RebalanceLayout,
+): Promise<boolean> {
+  const [{ log }, { getTmuxPath }, { runTmuxCommand }] = await Promise.all([
+    import("../../../shared"),
+    import("../../../tools/interactive-bash/tmux-path-resolver"),
+		import("../../../shared/tmux"),
+  ])
+
+  const tmuxPath = await getTmuxPath()
+  if (!tmuxPath) {
+    log("[rebalanceTeamWindow] SKIP: tmux not found", { windowId, layout })
+    return false
+  }
+
+  return rebalanceTeamWindowWith(windowId, layout, {
+    runTmux: (args) => runTmuxCommand(tmuxPath, args),
+    log,
+  })
+}