fix(app): default review tab to the branch diff on feature branches

packages/app/src/pages/session.tsx

@@ -56,6 +56,9 @@ import {
   createSessionTabs,
   createSizing,
   focusTerminalById,
+  resolveReviewChangeMode,
+  reviewChangeOptions,
+  type ReviewChangeMode,
   shouldFocusTerminalOnKeyDown,
   shouldShowFileTree,
 } from "@/pages/session/helpers"
@@ -82,13 +85,17 @@ type FollowupItem = FollowupDraft & { id: string }
 type FollowupEdit = Pick<FollowupItem, "id" | "prompt" | "context">
 const emptyFollowups: FollowupItem[] = []
 
-type ChangeMode = "git" | "branch" | "turn"
+type ChangeMode = ReviewChangeMode
 type VcsMode = "git" | "branch"
 
 const sessionViewState = () => ({
   messageId: undefined as string | undefined,
   mobileTab: "session" as "session" | "changes",
   changes: "git" as ChangeMode,
+  // Until the user explicitly picks a review mode, the default is auto-selected
+  // from changesOptions() so feature-branch sessions open on the full branch diff
+  // rather than working-tree-only ("git") changes.
+  changesTouched: false,
 })
 
 async function runPromptRollbackMutation<T, R>(input: {
@@ -358,17 +365,13 @@ export default function Page() {
     const project = sync().project
     return !!project && project.vcs !== "git"
   })
-  const changesOptions = createMemo<ChangeMode[]>(() => {
-    const list: ChangeMode[] = []
-    const project = sync().project
-    const vcs = sync().data.vcs
-    if (project?.vcs === "git") list.push("git")
-    if (project?.vcs === "git" && vcs?.branch && vcs?.default_branch && vcs.branch !== vcs.default_branch) {
-      list.push("branch")
-    }
-    list.push("turn")
-    return list
-  })
+  const changesOptions = createMemo<ChangeMode[]>(() =>
+    reviewChangeOptions({
+      vcs: sync().project?.vcs,
+      branch: sync().data.vcs?.branch,
+      defaultBranch: sync().data.vcs?.default_branch,
+    }),
+  )
   const mobileChanges = createMemo(() => !isDesktop() && store.mobileTab === "changes")
   const wantsReview = createMemo(() =>
     isDesktop()
@@ -736,11 +739,12 @@ export default function Page() {
 
   createEffect(() => {
     if (!sync().project) return
-    const list = changesOptions()
-    if (list.includes(store.changes)) return
-    const next = list[0]
-    if (!next) return
-    setStore("changes", next)
+    const next = resolveReviewChangeMode({
+      options: changesOptions(),
+      current: store.changes,
+      touched: store.changesTouched,
+    })
+    if (store.changes !== next) setStore("changes", next)
   })
 
   createEffect(
@@ -820,7 +824,7 @@ export default function Page() {
         options={changesOptions()}
         current={store.changes}
         label={label}
-        onSelect={(option) => option && setStore("changes", option)}
+        onSelect={(option) => option && setStore({ changes: option, changesTouched: true })}
         variant="ghost"
         size="small"
         valueClass="text-14-medium"

packages/app/src/pages/session/helpers.test.ts

@@ -7,6 +7,8 @@ import {
   createSessionTabs,
   focusTerminalById,
   getTabReorderIndex,
+  resolveReviewChangeMode,
+  reviewChangeOptions,
   shouldFocusTerminalOnKeyDown,
   shouldShowFileTree,
 } from "./helpers"
@@ -125,6 +127,54 @@ describe("getTabReorderIndex", () => {
   })
 })
 
+describe("reviewChangeOptions", () => {
+  test("prefers the branch diff on a feature-branch git session", () => {
+    expect(reviewChangeOptions({ vcs: "git", branch: "forge-task--abc", defaultBranch: "main" })).toEqual([
+      "branch",
+      "git",
+      "turn",
+    ])
+  })
+
+  test("omits branch when on the default branch", () => {
+    expect(reviewChangeOptions({ vcs: "git", branch: "main", defaultBranch: "main" })).toEqual(["git", "turn"])
+  })
+
+  test("omits branch when branch metadata is missing", () => {
+    expect(reviewChangeOptions({ vcs: "git" })).toEqual(["git", "turn"])
+  })
+
+  test("offers only turn diffs without git", () => {
+    expect(reviewChangeOptions({ vcs: "none" })).toEqual(["turn"])
+    expect(reviewChangeOptions({})).toEqual(["turn"])
+  })
+})
+
+describe("resolveReviewChangeMode", () => {
+  const options = reviewChangeOptions({ vcs: "git", branch: "forge-task--abc", defaultBranch: "main" })
+
+  test("auto-selects the branch diff when the user has not chosen a mode", () => {
+    expect(resolveReviewChangeMode({ options, current: "git", touched: false })).toBe("branch")
+  })
+
+  test("re-tracks the default even after an unrelated store default", () => {
+    expect(resolveReviewChangeMode({ options, current: "turn", touched: false })).toBe("branch")
+  })
+
+  test("keeps an explicit user choice", () => {
+    expect(resolveReviewChangeMode({ options, current: "git", touched: true })).toBe("git")
+    expect(resolveReviewChangeMode({ options, current: "turn", touched: true })).toBe("turn")
+  })
+
+  test("falls back to the default when the explicit choice is unavailable", () => {
+    expect(resolveReviewChangeMode({ options: ["git", "turn"], current: "branch", touched: true })).toBe("git")
+  })
+
+  test("returns the current mode when no options exist", () => {
+    expect(resolveReviewChangeMode({ options: [], current: "git", touched: false })).toBe("git")
+  })
+})
+
 describe("createSessionTabs", () => {
   test("normalizes the effective file tab", () => {
     createRoot((dispose) => {

packages/app/src/pages/session/helpers.ts

@@ -20,6 +20,40 @@ type TabsInput = {
 
 export const getSessionKey = (dir: string | undefined, id: string | undefined) => `${dir ?? ""}${id ? `/${id}` : ""}`
 
+export type ReviewChangeMode = "git" | "branch" | "turn"
+
+// Available review-tab change modes, in auto-default priority order. "branch"
+// (current branch vs default branch = the session's committed work) comes first
+// so a feature-branch session opens on the full task diff instead of
+// working-tree-only ("git") changes, which otherwise surface unrelated startup
+// drift (e.g. tooling that rewrites .opencode/package.json) as the "only" change.
+export function reviewChangeOptions(input: {
+  vcs?: string
+  branch?: string
+  defaultBranch?: string
+}): ReviewChangeMode[] {
+  const list: ReviewChangeMode[] = []
+  const isGit = input.vcs === "git"
+  if (isGit && input.branch && input.defaultBranch && input.branch !== input.defaultBranch) list.push("branch")
+  if (isGit) list.push("git")
+  list.push("turn")
+  return list
+}
+
+// Resolve the review mode to display. Until the user explicitly picks one
+// (`touched`), track the best default (options[0]); after that, keep their
+// choice and only fall back to the default when it is no longer available.
+export function resolveReviewChangeMode(input: {
+  options: ReviewChangeMode[]
+  current: ReviewChangeMode
+  touched: boolean
+}): ReviewChangeMode {
+  const next = input.options[0]
+  if (!next) return input.current
+  if (input.touched) return input.options.includes(input.current) ? input.current : next
+  return next
+}
+
 export function shouldShowFileTree(input: { visible: boolean; opened: boolean }) {
   return input.opened && input.visible
 }