fix: document apply ordering invariant; visible indeterminate checkbox + test

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwxdSt4reTm7Dj1oxRvpP3

web/src/components/DiffView.test.tsx

@@ -131,3 +131,25 @@ test("select-all header checkbox calls onToggleAllUpdates(true) when clicked whi
   await user.click(screen.getByRole("checkbox", { name: /выбрать все.*updates/i }))
   expect(onToggleAllUpdates).toHaveBeenCalledWith(true)
 })
+
+test("select-all header checkbox is indeterminate when only some update rows are selected", () => {
+  const csWithMultipleUpdates: ChangesetResponse = {
+    updates: [
+      { key: "A www.example.com.", kind: "update", type: "A", name: "www.example.com.", desired: ["1.1.1.1"], actual: ["9.9.9.9"], readOnly: false },
+      { key: "A api.example.com.", kind: "update", type: "A", name: "api.example.com.", desired: ["1.1.1.2"], actual: ["9.9.9.8"], readOnly: false },
+      { key: "A cdn.example.com.", kind: "update", type: "A", name: "cdn.example.com.", desired: ["1.1.1.3"], actual: ["9.9.9.7"], readOnly: false },
+    ],
+    prunes: [],
+    readOnly: [],
+    inSyncCount: 0,
+  }
+  renderDiff({
+    changeset: csWithMultipleUpdates,
+    // Partial selection: one of three keys — neither all nor none — is what
+    // must drive the header checkbox into the indeterminate ("mixed") state.
+    selectedUpdates: new Set(["A www.example.com."]),
+  })
+
+  const selectAll = screen.getByRole("checkbox", { name: /выбрать все.*updates/i })
+  expect(selectAll).toHaveAttribute("aria-checked", "mixed")
+})

web/src/components/ui/checkbox.tsx

@@ -8,7 +8,7 @@ function Checkbox({ className, ...props }: CheckboxPrimitive.Root.Props) {
     <CheckboxPrimitive.Root
       data-slot="checkbox"
       className={cn(
-        "peer relative flex size-4 shrink-0 items-center justify-center rounded-[4px] border border-input transition-colors outline-none group-has-disabled/field:opacity-50 after:absolute after:-inset-x-3 after:-inset-y-2 focus-visible:border-ring focus-visible:ring-3 focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-3 aria-invalid:ring-destructive/20 aria-invalid:aria-checked:border-primary dark:bg-input/30 dark:aria-invalid:border-destructive/50 dark:aria-invalid:ring-destructive/40 data-checked:border-primary data-checked:bg-primary data-checked:text-primary-foreground dark:data-checked:bg-primary",
+        "peer relative flex size-4 shrink-0 items-center justify-center rounded-[4px] border border-input transition-colors outline-none group-has-disabled/field:opacity-50 after:absolute after:-inset-x-3 after:-inset-y-2 focus-visible:border-ring focus-visible:ring-3 focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-3 aria-invalid:ring-destructive/20 aria-invalid:aria-checked:border-primary dark:bg-input/30 dark:aria-invalid:border-destructive/50 dark:aria-invalid:ring-destructive/40 data-checked:border-primary data-checked:bg-primary data-checked:text-primary-foreground dark:data-checked:bg-primary data-indeterminate:border-primary data-indeterminate:bg-primary/40 data-indeterminate:text-primary-foreground",
         className
       )}
       {...props}