spa: a blank page can never be silent again

boot-guard.js is a classic script loaded before the module graph, so it
survives the graph failing to link. If #app is still empty after ten
seconds it names what failed and offers a reset of this origin — cache,
storage, databases and the service worker, which clearing the cache does
not touch.

Two real defects found building it: openDB never settled when an upgrade
was blocked by another tab, and a connection it gave up on stayed open
and squatted the database.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/api/webapp.py b/packages/meshbay-hub/src/meshbay_hub/api/webapp.py
index 6ac5cdb..3e23961 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/webapp.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/webapp.py
@@ -180,6 +180,10 @@ _HTML = """\
        and app.js's own relative imports inherit the prefix, which is the only
        way the module graph is guaranteed not to be a mixture of two builds.
        See _asset_version() and VersionedStatics. -->
+  <!-- First, and not a module: if the graph below never links, no module code
+       runs at all, and this is what keeps the page from being silently blank.
+       It draws nothing unless #app is still empty ten seconds from now. -->
+  <script src="/a/{v}/boot-guard.js"></script>
   <!-- Argon2id (WebAssembly, inlined) — WebCrypto has no memory-hard KDF, and the
        keypair bundle needs one: it is protected by the passphrase alone and sits
        on every node its owner joins (C4). Vendored, see static/vendor/PROVENANCE.md -->