feat(client): fetch the media apps, the player, settings and search on first use

apps.js registers Videos, Music, Photos and every settings pane through
lazy.js; the group page does the same for the video player and the
settings panel, and the shell for the search page. The first download
goes from 49 modules / 386 KB gzip to 37 / 289 KB; opening Music now
fetches music-app.js and media-tiles.js and nothing of Videos.
test_first_load_is_lean holds the eager graph; test_spa_imports checks
that every on-demand load names an export that exists.

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

1 files changed, 54 insertions, 0 deletions

diff --git a/packages/meshbay-hub/tests/test_first_load_is_lean.py b/packages/meshbay-hub/tests/test_first_load_is_lean.py
new file mode 100644
index 0000000..74cd880
--- /dev/null
+++ b/packages/meshbay-hub/tests/test_first_load_is_lean.py
@@ -0,0 +1,54 @@
+"""
+What a browser downloads before the first screen renders.
+
+ES modules load their static `import` graph up front, whether the visitor opens
+what it leads to or not. The Videos, Music and Photos apps, the video player,
+the group settings and the search page used to be part of it — about a quarter
+of the client, paid by a member who only opens the chat. They are now fetched
+the first time they are shown (lazy.js); one static import added back anywhere
+on the path from app.js would quietly undo that, and nothing else would fail.
+"""
+
+import re
+from pathlib import Path
+
+STATIC = Path(__file__).resolve().parents[1] / "src" / "meshbay_hub" / "static"
+
+STATIC_IMPORT = re.compile(
+    r"""^\s*(?:import|export)\b[^'";]*?\bfrom\s*['"]\./([^'"]+)['"]"""
+    r"""|^\s*import\s*['"]\./([^'"]+)['"]""", re.M)
+
+# Loaded on demand, never at start-up.
+ON_DEMAND = {
+    "video-app.js", "music-app.js", "photos-app.js", "helloworld-app.js",
+    "chat-app-settings.js", "video-app-settings.js", "music-app-settings.js",
+    "photos-app-settings.js", "helloworld-app-settings.js",
+    "video-player.js", "group-settings.js", "search-page.js",
+}
+
+
+def _eager() -> set[str]:
+    seen, stack = set(), ["app.js"]
+    while stack:
+        name = stack.pop()
+        if name in seen or not (STATIC / name).exists():
+            continue
+        seen.add(name)
+        text = (STATIC / name).read_text(encoding="utf-8")
+        stack += [a or b for a, b in STATIC_IMPORT.findall(text)]
+    return seen
+
+
+def test_the_first_download_leaves_the_apps_out():
+    eager = _eager()
+    assert len(eager) > 20, "the import graph was not followed — re-read this test"
+    brought_back = sorted(eager & ON_DEMAND)
+    assert not brought_back, (
+        f"loaded at start-up again: {brought_back} — a static import on the "
+        f"path from app.js; import it through lazy.js instead")
+
+
+def test_every_module_loaded_on_demand_still_exists():
+    """A rename would make the check above pass for a file nobody serves."""
+    missing = sorted(n for n in ON_DEMAND if not (STATIC / n).exists())
+    assert not missing, missing