refactor(branch-selector): address qa-swarm review nits

Multi-perspective review (paul + xp + security-audit) surfaced low/nit items;
this addresses the actionable ones:

- Extract the duplicated "Loading branches…" literal into a shared
  LOADING_BRANCHES_LABEL const so the two render sites can't drift.
- Clarify the TaskInput comment: the cached default is best-effort — a
  default branch renamed since it was cached stays seeded until the user
  picks another (the auto-select only fires while nothing is selected).
- Lock the empty-state gating with a test asserting "No branches found."
  keeps the `hidden` class when the seeded trunk row makes the list
  non-empty, so it never flashes above the seeded row.

security-audit: 0 findings (API-derived branch name → auto-escaped React
text + the pre-existing selection path; no new sink).

Generated-By: PostHog Code
Task-Id: 562fb90f-d823-425d-b53c-5f482b55a8b2

Author: pauldambra

packages/ui/src/features/git-interaction/components/BranchSelector.test.tsx

@@ -96,6 +96,11 @@ describe("BranchSelector cloud mode", () => {
 
     expect(await screen.findByRole("option", { name: "main" })).toBeVisible();
     expect(screen.getByText("Loading branches…")).toBeVisible();
+    // The seeded row makes the list non-empty, so the empty-state stays gated
+    // off (Base UI only reveals it when the content group is data-empty) — it
+    // keeps the `hidden` class rather than flashing "No branches found." above
+    // the trunk row.
+    expect(screen.getByText("No branches found.")).toHaveClass("hidden");
   });
 
   it("does not seed the default branch once the user is searching", async () => {

packages/ui/src/features/git-interaction/components/BranchSelector.tsx

@@ -40,6 +40,10 @@ import { getSuggestedBranchName } from "../utils/getSuggestedBranchName";
 
 const COMBOBOX_LIMIT = 50;
 
+// Shared so the two "still loading branches" render sites (the empty-list
+// spinner and the seeded-default row) can never drift out of sync on a copy edit.
+const LOADING_BRANCHES_LABEL = "Loading branches…";
+
 // Sentinel value for the "Create new branch" action. Rendered as a real
 // ComboboxItem in the list footer so it's reachable by keyboard, not a
 // plain button the combobox's roving focus skips over.
@@ -472,7 +476,7 @@ export function BranchSelector({
         ) : null}
 
         {branchListLoading && branches.length === 0 ? (
-          <LoadingRow label="Loading branches…" />
+          <LoadingRow label={LOADING_BRANCHES_LABEL} />
         ) : (
           <ComboboxEmpty>No branches found.</ComboboxEmpty>
         )}
@@ -540,7 +544,9 @@ export function BranchSelector({
           item while the remote list loads. A loading row directly below it
           makes clear the rest of the branches are still on the way.
         */}
-        {seededDefaultBranch ? <LoadingRow label="Loading branches…" /> : null}
+        {seededDefaultBranch ? (
+          <LoadingRow label={LOADING_BRANCHES_LABEL} />
+        ) : null}
 
         {isCloudMode && cloudBranchesHasMore ? (
           <ComboboxListFooter>

packages/ui/src/features/task-detail/components/TaskInput.tsx

@@ -435,7 +435,10 @@ export function TaskInput({
   const liveCloudDefaultBranch = cloudBranchData?.defaultBranch ?? null;
   // Serve the persisted default branch until the live list resolves, so the
   // majority "start on trunk" case pre-selects trunk with zero wait on a cold
-  // start. Falls through to the fresh value the moment it arrives.
+  // start. The cached value is best-effort: `cloudDefaultBranch` switches to the
+  // live value the moment it arrives, but the picker's auto-select only fires
+  // while nothing is selected — so a default branch renamed since it was cached
+  // (rare) would leave the seeded name selected until the user picks another.
   const cloudDefaultBranch =
     liveCloudDefaultBranch ??
     (selectedCloudRepository