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>

2 files changed, 84 insertions, 3 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
diff --git a/packages/meshbay-hub/tests/test_spa_imports.py b/packages/meshbay-hub/tests/test_spa_imports.py
index 230f33f..8be70cb 100644
--- a/packages/meshbay-hub/tests/test_spa_imports.py
+++ b/packages/meshbay-hub/tests/test_spa_imports.py
@@ -79,9 +79,36 @@ def test_the_check_can_see_a_real_module():
     finding imports would make the test above pass over an empty set, which
     looks exactly like success.
     """
-    source = (STATIC / "apps.js").read_text(encoding="utf-8")
+    source = (STATIC / "group-page.js").read_text(encoding="utf-8")
     found = IMPORT.findall(source)
     assert len(found) >= 5, (
-        "the import pattern no longer matches apps.js — this test is then "
+        "the import pattern no longer matches group-page.js — this test is then "
         "checking nothing")
-    assert "configurableApps" in _exported(source)
+    assert "GroupPage" in _exported(source)
+
+
+# `lazy(() => import('./x.js'), 'Name')` (lazy.js), and the hand-written form
+# `import('./x.js').then(m => { _Page = m.Name; ...`.
+LAZY = re.compile(r"lazy\(\s*\(\)\s*=>\s*import\('\./([^']+)'\),\s*'(\w+)'")
+THEN = re.compile(r"import\('\./([^']+)'\)\.then\(\s*m\s*=>\s*\{\s*\w+\s*=\s*m\.(\w+)")
+
+
+def test_every_module_loaded_on_demand_exports_what_is_asked_for():
+    """
+    The same fault as above, one step later: a component fetched on demand
+    under a name its module does not export renders a spinner that never
+    ends — no error, since the fetch itself succeeded.
+    """
+    problems, seen = [], 0
+    for path in sorted(STATIC.glob("*.js")):
+        source = path.read_text(encoding="utf-8")
+        for spec, name in LAZY.findall(source) + THEN.findall(source):
+            seen += 1
+            target = STATIC / spec
+            if not target.exists():
+                problems.append(f"{path.name}: loads ./{spec} — no such file")
+            elif name not in _exported(target.read_text(encoding="utf-8")):
+                problems.append(f"{path.name}: loads {{{name}}} from ./{spec}, "
+                                f"which does not export it")
+    assert seen >= 15, f"only {seen} on-demand loads found — is the pattern stale?"
+    assert not problems, "unresolved on-demand loads:\n" + "\n".join(problems)