2 files changed, 18 insertions, 1 deletions
diff --git a/packages/app/src/pages/session/helpers.test.ts b/packages/app/src/pages/session/helpers.test.ts
index 0afc7eb6a..d877d5b2e 100644
--- a/packages/app/src/pages/session/helpers.test.ts
+++ b/packages/app/src/pages/session/helpers.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test"
-import { combineCommandSections, createOpenReviewFile, focusTerminalById } from "./helpers"
+import { combineCommandSections, createOpenReviewFile, focusTerminalById, getTabReorderIndex } from "./helpers"
 
 describe("createOpenReviewFile", () => {
   test("opens and loads selected review file", () => {
@@ -59,3 +59,13 @@ describe("combineCommandSections", () => {
     expect(result.map((item) => item.id)).toEqual(["a", "b", "c"])
   })
 })
+
+describe("getTabReorderIndex", () => {
+  test("returns target index for valid drag reorder", () => {
+    expect(getTabReorderIndex(["a", "b", "c"], "a", "c")).toBe(2)
+  })
+
+  test("returns undefined for unknown droppable id", () => {
+    expect(getTabReorderIndex(["a", "b", "c"], "a", "missing")).toBeUndefined()
+  })
+})
diff --git a/packages/app/src/pages/session/helpers.ts b/packages/app/src/pages/session/helpers.ts
index d9ce90793..dcf2c8784 100644
--- a/packages/app/src/pages/session/helpers.ts
+++ b/packages/app/src/pages/session/helpers.ts
@@ -36,3 +36,10 @@ export const createOpenReviewFile = (input: {
 export const combineCommandSections = (sections: readonly (readonly CommandOption[])[]) => {
   return sections.flatMap((section) => section)
 }
+
+export const getTabReorderIndex = (tabs: readonly string[], from: string, to: string) => {
+  const fromIndex = tabs.indexOf(from)
+  const toIndex = tabs.indexOf(to)
+  if (fromIndex === -1 || toIndex === -1 || fromIndex === toIndex) return undefined
+  return toIndex
+}