From f4fd6db8faa15bf02f38a14b652cc46936f8d6bf Mon Sep 17 00:00:00 2001
From: Christophe Besson <cbesson@gmail.com>
Date: Thu, 17 Sep 2026 03:40:52 +0200
Subject: spa: a blank page can never be silent again
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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>
---
 packages/meshbay-hub/src/meshbay_hub/api/webapp.py |   4 +
 .../src/meshbay_hub/static/boot-guard.js           | 200 +++++++++++++++++++++
 .../src/meshbay_hub/static/hub-client.js           |  37 +++-
 3 files changed, 239 insertions(+), 2 deletions(-)
 create mode 100644 packages/meshbay-hub/src/meshbay_hub/static/boot-guard.js

(limited to 'packages/meshbay-hub/src')

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 -->
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/boot-guard.js b/packages/meshbay-hub/src/meshbay_hub/static/boot-guard.js
new file mode 100644
index 0000000..f5e3aa1
--- /dev/null
+++ b/packages/meshbay-hub/src/meshbay_hub/static/boot-guard.js
@@ -0,0 +1,200 @@
+/**
+ * The page can never stay silently blank.
+ *
+ * A reader once had nothing but white for an evening: the shell arrived, the
+ * modules were served from the browser's own store so not one request reached
+ * the hub, and nothing ever rendered. No message, no error on screen, nothing
+ * in the server's log to look at — the same account worked in a private window
+ * and in another browser, which is the signature of something wrong in this
+ * origin's stored state rather than in what was deployed. Clearing the site's
+ * data fixed it. Clearing the *cache*, three times, had not: a service worker
+ * and IndexedDB are not the cache, and nothing on screen said so.
+ *
+ * This answers the *silence*, not whatever caused it. A blank page is a bug
+ * report nobody can write, and a phone has no console to open.
+ *
+ * **A classic script, deliberately, and first.** The failure it guards against
+ * includes the module graph never linking — one bad module and no module code
+ * runs at all, so a guard inside `app.js` would be part of what failed. This
+ * one has no imports and cannot be stopped by them.
+ *
+ * It does nothing when the application mounts, which is the ordinary case: it
+ * looks once, late, and speaks only to a reader already staring at nothing.
+ */
+(function () {
+  'use strict';
+
+  // Long enough that a cold phone on a slow network is never interrupted —
+  // argon2's wasm, forty modules and a catalogue — and short enough that
+  // nobody sits in front of white wondering. The app mounts in well under two
+  // seconds when it mounts at all.
+  var GIVE_UP_MS = 10000;
+  var problems = [];
+
+  function note(what) {
+    if (problems.length < 5) problems.push(String(what).slice(0, 200));
+  }
+
+  // Capture phase: a `<script>` or stylesheet that fails to load fires `error`
+  // at the element, and that one does not bubble.
+  window.addEventListener('error', function (e) {
+    if (e && e.target && e.target !== window && e.target.src) {
+      note('could not load ' + String(e.target.src).replace(/^https?:\/\/[^/]+/, ''));
+    } else if (e && e.message) {
+      note(e.message);
+    }
+  }, true);
+
+  window.addEventListener('unhandledrejection', function (e) {
+    var r = e && e.reason;
+    note((r && (r.message || r)) || 'a promise rejected');
+  });
+
+  var FR = (navigator.language || '').toLowerCase().indexOf('fr') === 0;
+  var TEXT = FR ? {
+    title: 'MeshBay n’a pas pu démarrer',
+    body: 'L’application s’est arrêtée avant d’afficher quoi que ce soit. '
+        + 'Cela vient presque toujours des données que ce navigateur garde pour ce site.',
+    retry: 'Réessayer',
+    reset: 'Réinitialiser les données de ce site',
+    warn: 'Vous devrez vous reconnecter. Vos fichiers et vos groupes ne sont pas '
+        + 'touchés : ils vivent sur les nœuds, pas ici.',
+    doing: 'Réinitialisation…',
+    blocked: 'Un autre onglet de ce site garde la base ouverte. Fermez les autres '
+           + 'onglets meshbay, puis réessayez.',
+  } : {
+    title: 'MeshBay could not start',
+    body: 'The application stopped before it drew anything. This is almost always '
+        + 'the data this browser keeps for this site.',
+    retry: 'Try again',
+    reset: 'Reset this site’s data',
+    warn: 'You will have to sign in again. Your files and groups are untouched: '
+        + 'they live on the nodes, not here.',
+    doing: 'Resetting…',
+    blocked: 'Another tab of this site is holding the database open. Close the '
+           + 'other meshbay tabs, then try again.',
+  };
+
+  /**
+   * Deleting a database waits for every connection to it to close, and another
+   * tab of this site is a connection. Unwatched, `deleteDatabase` then does
+   * nothing at all and says nothing — so this page would reload into the state
+   * it had just promised to clear, which is the bug this file exists to end.
+   * Blocked deletions are named and handed back.
+   */
+  function dropDatabase(name) {
+    return new Promise(function (res) {
+      var req;
+      try { req = indexedDB.deleteDatabase(name); } catch (e) { return res(null); }
+      var settled = false;
+      var end = function (v) { if (!settled) { settled = true; res(v); } };
+      req.onsuccess = function () { end(null); };
+      req.onerror = function () { end(null); };
+      req.onblocked = function () { end(name); };
+      setTimeout(function () { end(name); }, 2500);
+      return undefined;
+    });
+  }
+
+  /** Everything this origin holds, and the service worker with it. */
+  function resetSiteData(done) {
+    var waiting = [];
+    var blocked = [];
+    try { localStorage.clear(); } catch (e) { /* private mode */ }
+    try { sessionStorage.clear(); } catch (e) { /* private mode */ }
+
+    if (window.indexedDB) {
+      var names = indexedDB.databases
+        ? indexedDB.databases().then(function (dbs) {
+            return (dbs || []).map(function (d) { return d && d.name; }).filter(Boolean);
+          }).catch(function () { return ['meshbay', 'meshbay_keys']; })
+        // Safari and older engines have no `databases()`; these are ours.
+        : Promise.resolve(['meshbay', 'meshbay_keys']);
+      waiting.push(names.then(function (list) {
+        return Promise.all(list.map(dropDatabase)).then(function (results) {
+          results.forEach(function (n) { if (n) blocked.push(n); });
+        });
+      }).catch(function () {}));
+    }
+
+    if (window.caches && caches.keys) {
+      waiting.push(caches.keys().then(function (keys) {
+        return Promise.all((keys || []).map(function (k) { return caches.delete(k); }));
+      }).catch(function () {}));
+    }
+
+    if (navigator.serviceWorker && navigator.serviceWorker.getRegistrations) {
+      waiting.push(navigator.serviceWorker.getRegistrations().then(function (regs) {
+        return Promise.all((regs || []).map(function (r) { return r.unregister(); }));
+      }).catch(function () {}));
+    }
+
+    // Bounded: a hung unregister must not leave the reader on "Resetting…" for
+    // ever, which would be this bug wearing a different hat.
+    var fired = false;
+    var finish = function () { if (!fired) { fired = true; done(blocked); } };
+    Promise.all(waiting).then(finish).catch(finish);
+    setTimeout(finish, 4000);
+  }
+
+  function el(tag, style, text) {
+    var n = document.createElement(tag);
+    if (style) n.setAttribute('style', style);
+    if (text) n.textContent = text;
+    return n;
+  }
+
+  function show(root) {
+    var BTN = 'display:block;width:100%;margin:8px 0;padding:12px 16px;font:inherit;'
+            + 'font-size:15px;border-radius:8px;border:1px solid #c9ccd1;background:#fff;'
+            + 'color:#111;cursor:pointer';
+    var box = el('div', 'max-width:34em;margin:12vh auto;padding:0 20px;'
+      + 'font:15px/1.55 system-ui,-apple-system,Segoe UI,Roboto,sans-serif;color:#111');
+
+    box.appendChild(el('h1', 'font-size:20px;margin:0 0 12px', TEXT.title));
+    box.appendChild(el('p', 'margin:0 0 16px;color:#444', TEXT.body));
+
+    var retry = el('button', BTN, TEXT.retry);
+    retry.addEventListener('click', function () { location.reload(); });
+    box.appendChild(retry);
+
+    var reset = el('button', BTN + ';border-color:#b23;color:#b23', TEXT.reset);
+    reset.addEventListener('click', function () {
+      reset.disabled = true;
+      reset.textContent = TEXT.doing;
+      resetSiteData(function (blocked) {
+        if (!blocked.length) { location.reload(); return; }
+        // Reloading here would be a lie: the database is still there, held by
+        // another tab, and the page would come back exactly as broken.
+        reset.disabled = false;
+        reset.textContent = TEXT.reset;
+        var why = el('p', 'margin:12px 0 0;color:#b23;font-size:13px',
+          TEXT.blocked + ' (' + blocked.join(', ') + ')');
+        why.setAttribute('data-blocked', blocked.join(','));
+        box.appendChild(why);
+      });
+    });
+    box.appendChild(reset);
+
+    box.appendChild(el('p', 'margin:12px 0 0;color:#666;font-size:13px', TEXT.warn));
+
+    if (problems.length) {
+      // Verbatim, and on screen. Nothing else reaches a reader who cannot open
+      // a console, and it is the first thing anybody diagnosing this will ask.
+      var pre = el('pre', 'margin:16px 0 0;padding:10px;background:#f3f4f6;'
+        + 'border-radius:6px;font-size:12px;white-space:pre-wrap;word-break:break-word;'
+        + 'color:#333', problems.join('\n'));
+      box.appendChild(pre);
+    }
+
+    root.appendChild(box);
+  }
+
+  setTimeout(function () {
+    var root = document.getElementById('app');
+    // Mounted, which is the ordinary case and the end of this script's
+    // involvement. A later render replaces whatever is here anyway.
+    if (!root || root.firstChild) return;
+    show(root);
+  }, GIVE_UP_MS);
+}());
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/hub-client.js b/packages/meshbay-hub/src/meshbay_hub/static/hub-client.js
index dbd5037..eead457 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/hub-client.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/hub-client.js
@@ -18,6 +18,7 @@ const IDB_NAME = 'meshbay';
 // disagreeing about the version is a `VersionError` thrown at whichever of
 // them happens to run second.
 const IDB_VERSION = 2;
+const OPEN_DB_TIMEOUT_MS = 5000;
 const IDB_STORE = 'group_indexes';
 const IDB_PLAYLISTS = 'playlists';
 
@@ -27,9 +28,32 @@ function navigate(path) {
 
 // ── IndexedDB cache ─────────────────────────────────────────────────────────
 
+/**
+ * The database, opened — or refused, but never left hanging.
+ *
+ * A version upgrade waits for every other connection to this database to
+ * close. A second tab of this site holding version 1 open is enough to stop
+ * it, and `indexedDB.open` then fires **neither** `success` nor `error`: it
+ * fires `blocked`, and if nothing handles that the promise never settles. Every
+ * `await openDB()` behind it waits for ever, which reads as a feature that
+ * silently does nothing rather than as a failure anybody can see.
+ *
+ * So `blocked` is heard, and a deadline covers the rest. Callers already treat
+ * a rejection as "no local cache this time" and carry on.
+ */
 function openDB() {
   return new Promise((resolve, reject) => {
     const req = indexedDB.open(IDB_NAME, IDB_VERSION);
+    let settled = false;
+    const done = (fn, arg) => { if (!settled) { settled = true; fn(arg); } };
+    // Generous: the other tab is asked to close and usually does within a
+    // frame. This is the backstop for the one that cannot — a page suspended
+    // on a phone, say — not a latency budget.
+    const deadline = setTimeout(() => done(reject, new Error(
+      'IndexedDB open timed out (another tab may hold an older version open)')),
+      OPEN_DB_TIMEOUT_MS);
+    req.onblocked = () => done(reject, new Error(
+      'IndexedDB upgrade blocked by another tab of this site'));
     req.onupgradeneeded = () => {
       const db = req.result;
       if (!db.objectStoreNames.contains(IDB_STORE)) {
@@ -43,8 +67,17 @@ function openDB() {
         db.createObjectStore(IDB_PLAYLISTS);
       }
     };
-    req.onsuccess = () => resolve(req.result);
-    req.onerror = () => reject(req.error);
+    req.onsuccess = () => {
+      clearTimeout(deadline);
+      // Giving up does not cancel the request: the other tab eventually closes,
+      // the upgrade goes through, and this fires with a live connection nobody
+      // is waiting for. Left open it squats the database — blocking the next
+      // upgrade *and* any attempt to delete it, which is the failure this
+      // whole guard exists to end, arriving through the back door.
+      if (settled) { try { req.result.close(); } catch { /* already gone */ } return; }
+      done(resolve, req.result);
+    };
+    req.onerror = () => { clearTimeout(deadline); done(reject, req.error); };
   });
 }
 
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