fix(browser): click by index reaches the last read's element

CHANGELOG.md

@@ -12,6 +12,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - The crosshair on a session browser's toolbar lets you leave notes on the page for the agent. The element under the pointer is outlined and named, a click opens a note beside it, and each note pins its element with a number, following it as the page scrolls. Notes wait in a tray floating over the bottom of the page, which never resizes under you. Hovering a note there lights its element, a click edits it, and Send (or Ctrl+Enter) types them into the session as one message: which element, a selector the agent's `browser_click` takes, the React component that drew it in a development build, and your note. Ctrl+Shift+E (Cmd+Shift+E on macOS) turns the crosshair on and off, and Esc leaves it. A send the session refuses keeps the notes and says why in the tray.
 - A session's browser downloads files. A download the page starts, from a link, a button, a new tab or a script, lands in your Downloads folder under the name the page gives it, with ` (1)` added rather than overwriting a file already there. The agent can also open a file's URL directly. The agent's click, key press or open answers with the file's path and size, and the window shows a toast naming the file, with a button that opens its folder. Before, a download button in the session's browser did nothing.
 
+### Fixed
+
+- A session browser's click, type or key press by index reaches the element the agent's last page read gave that index. After a scroll and a second read, an element the first read had listed under the same index, now out of view, could take the click instead, with no error.
+
 ## [0.80.0] - 2026-10-27
 
 > [!IMPORTANT]

internal/browser/chrome_live_test.go

@@ -379,3 +379,47 @@ func TestChromeClickRefusesAPointOutsideTheViewport(t *testing.T) {
 		t.Fatalf("click at 400,715 in an 800x600 viewport: %v, want an error naming the viewport", err)
 	}
 }
+
+func TestChromeClickByIndexHitsTheLastReadNotAnEarlierOne(t *testing.T) {
+	p, _ := liveChrome(t)
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "text/html")
+		fmt.Fprint(w, `<body style="margin:0">
+<button onclick="document.body.dataset.hit = 'top'">Top</button>
+<div style="height:3000px"></div>
+<button onclick="document.body.dataset.hit = 'bottom'">Bottom</button></body>`)
+	}))
+	t.Cleanup(srv.Close)
+	ctx, cancel := context.WithTimeout(context.Background(), pageWait)
+	defer cancel()
+	if err := p.Navigate(ctx, srv.URL); err != nil {
+		t.Fatal(err)
+	}
+	if err := p.Resize(ctx, Viewport{W: 800, H: 600, Scale: 1}); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := p.Info(ctx); err != nil {
+		t.Fatal(err)
+	}
+	if err := p.run(ctx, chromedp.Evaluate(`window.scrollTo(0, document.body.scrollHeight)`, nil)); err != nil {
+		t.Fatal(err)
+	}
+	info, err := p.Info(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(info.Interactive) != 1 || info.Interactive[0].Text != "Bottom" {
+		t.Fatalf("second read listed %+v, want only Bottom", info.Interactive)
+	}
+	index := info.Interactive[0].Index
+	if _, _, err := p.Click(ctx, Target{Index: &index}); err != nil {
+		t.Fatal(err)
+	}
+	var hit string
+	if err := p.run(ctx, chromedp.Evaluate(`document.body.dataset.hit || ""`, &hit)); err != nil {
+		t.Fatal(err)
+	}
+	if hit != "bottom" {
+		t.Fatalf("index %d from the last read clicked %q, want bottom", index, hit)
+	}
+}

internal/browser/pageinfo.go

@@ -4,6 +4,11 @@ package browser
 // data-lich-idx so a later click/type can find the same node, and it never
 // reads a form control's value into the result.
 //
+// Each read first wipes the stamps of the one before. An element scrolled out
+// of view keeps no index, so the index the last read gave to another element
+// cannot resolve to it; an index the last read did not hand out finds nothing
+// and click/type report the page changed.
+//
 // A password input has no innerText, so an innerText || value label chain
 // hands the live credential to the agent and into the session transcript.
 // Rather than classify which fields are sensitive — type === 'password' is
@@ -51,6 +56,7 @@ const pageInfoScript = `(() => {
       attr(el, 'name')
     ).trim();
   };
+  document.querySelectorAll('[data-lich-idx]').forEach((el) => el.removeAttribute('data-lich-idx'));
   const els = [...document.querySelectorAll(sel)].filter(isVisible);
   const interactive = els.slice(0, 200).map((el, i) => {
     el.setAttribute('data-lich-idx', String(i));