Telemetry: boot-slow beacon names the 3 slowest resources

The first boot-slow capture (5763ms total, html 68ms) proved the white screen
happens AFTER the shell arrives — but not which fetch eats the time. Append
the 3 slowest resource entries (path, start→end, transferSize; sz0 ≈ served
from SW/cache) so the next slow boot names its culprit. Reason cap 300→500
client+server to fit the detail.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/app.html

@@ -42,7 +42,7 @@
         function report(reason) {
           if (sent) return; sent = true;             // one beacon per page
           try {
-            var b = new Blob([JSON.stringify({ reason: String(reason || 'unknown').slice(0, 300),
+            var b = new Blob([JSON.stringify({ reason: String(reason || 'unknown').slice(0, 500),
                                                path: location.pathname })], { type: 'application/json' });
             navigator.sendBeacon && navigator.sendBeacon('/api/client-error', b);
           } catch (e) { /* best-effort telemetry */ }
@@ -73,6 +73,16 @@
               if (nav && nav.responseStart) detail += ' (html ' + Math.round(nav.responseStart) + 'ms)';
               if (navigator.connection && navigator.connection.effectiveType)
                 detail += ' on ' + navigator.connection.effectiveType;
+              // Name the culprits: the 3 slowest resource fetches so far, with
+              // start→end so gaps (idle/SW churn) are distinguishable from slow
+              // downloads. size=0 usually means it came from the SW/cache.
+              var res = (performance.getEntriesByType('resource') || [])
+                .slice().sort(function (a, b) { return b.duration - a.duration; }).slice(0, 3)
+                .map(function (r) {
+                  var name = r.name.replace(location.origin, '').slice(0, 80);
+                  return name + ' ' + Math.round(r.startTime) + '→' + Math.round(r.responseEnd) + 'ms sz' + (r.transferSize || 0);
+                });
+              if (res.length) detail += ' | slowest: ' + res.join(' ; ');
               report(detail);
             }
           } catch (e) { /* timing is best-effort */ }

goodnews/api.py

@@ -948,7 +948,7 @@ def create_app() -> FastAPI:
         with get_conn() as conn:
             conn.execute(
                 "INSERT INTO client_errors (reason, path, user_agent, app_version) VALUES (?, ?, ?, ?)",
-                ((body.reason or "")[:300], (body.path or "")[:200], ua, (body.version or "")[:60]),
+                ((body.reason or "")[:500], (body.path or "")[:200], ua, (body.version or "")[:60]),
             )
             conn.execute("DELETE FROM client_errors WHERE created_at < datetime('now','-14 days')")
             conn.commit()