A reload offer only for a page that is older, and a tab switch that moves one scroller

The update toast fired whenever a service worker was waiting, so after every
release it appeared on pages that were already the release -- including one
fetched with Ctrl+Shift+R. It now compares the waiting worker's release with
the page's own, and so does the reload that follows another tab accepting it.

On Admin -> Prompts, visually hidden labels were positioned against the page
and made the document 6771px tall behind an overflow-hidden root; the tab
handler's scrollIntoView then scrolled that root and lifted the shell 56px.
Every scroll region is now a containing block, and the handler moves only the
container that scrolls.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_pwa.py

@@ -311,3 +311,33 @@ def test_the_worker_precaches_what_a_page_will_ask_for():
     source = (STATIC_DIR / "js" / "sw.js").read_text()
     assert 'path + "?v=" + VERSION' in source
     assert "versioned(path)" in source
+
+
+def test_the_update_offer_asks_whether_this_page_is_older(client: TestClient, registered):
+    """After a release the toast offered a reload on every page, including one
+    just fetched with Ctrl+Shift+R, and reloading never made it go away. It
+    fired whenever a worker was waiting. But a page loaded after the update
+    already IS the update: it comes from the network, and every asset it names
+    carries `?v=`. The worker that waits is nearly always the previous one,
+    still holding the tab, because a reload never lets it run out of pages.
+
+    So the offer, and the automatic reload when another tab accepts it, compare
+    the worker's release with the page's own. Driven under Node against stubs
+    before committing: 1.8.3 offered a reload to a current page and to a page
+    that another tab's Reload had just made current. This does neither, and
+    still offers it to a page from an older release.
+    """
+    import re
+
+    import lembas
+
+    page = client.get("/chat").text
+    assert f"window.lembasRelease = \"{lembas.__version__}\";" in page
+
+    source = (STATIC_DIR / "js" / "app.js").read_text()
+    code = re.sub(r"/\*.*?\*/", "", source, flags=re.S)
+    start = code.index("function watchForUpdate")
+    block = code[start : code.index("navigator.serviceWorker.ready.then(watchForUpdate)")]
+    # Both ways a waiting worker is found, and the controllerchange reload.
+    assert block.count("isNewerThanThisPage(") == 3
+    assert 'searchParams.get("v")' in code

tests/test_ui_js.py

@@ -177,6 +177,30 @@ def test_the_tab_reset_finds_the_container_that_actually_scrolls():
     assert "scrollHeight > " in SOURCE
 
 
+def test_a_tab_switch_moves_only_the_container_that_scrolls():
+    """Switching a tab on /admin/prompts lifted the whole shell 56px, with the
+    topbar gone off the top and a strip of bare background under everything.
+
+    Two halves, and either one alone is enough to bring it back. The prompt
+    cards' `.visually-hidden` labels are `position: absolute`. With no
+    positioned ancestor they were placed against the page and stretched the
+    document to 6771px behind an `overflow: hidden` root. And the handler used
+    `scrollIntoView`, which scrolls every ancestor that can scroll, the root
+    included. Measured in headless Chromium at 1640x930 before and after.
+    """
+    app = (ROOT / "web/static/css/app.css").read_text(encoding="utf-8")
+    start = app.index(".scroll-region,")
+    rule = app[start : app.index("}", start)]
+    assert ".admin-scroll" in rule
+    assert "position: relative" in rule
+
+    code = re.sub(r"/\*.*?\*/", "", SOURCE, flags=re.S)
+    start = code.index('closest(".tabs__bar")')
+    handler = code[start : code.index("})();", start)]
+    assert "scrollIntoView" not in handler
+    assert "outer.scrollTop" in handler
+
+
 def test_the_two_ends_of_the_shell_stay_level():
     """The sidebar footer and the composer sit either side of the same vertical
     edge and are both content-sized, so without a common floor they end at