Steadier page loads and web search

Three small things that could go wrong at the edges no longer do.

When an agent searched the web and one of the results pointed at a page that had since been removed, the whole page fetch failed. Now the missing page is simply reported as missing and the agent carries on with the other results.

Occasionally a page load could fail outright because the browser measurement the layout depends on ran before the script that provides it had loaded. The measurement now brings its own script along, so the order no longer matters.

Finally, a portal that starts up while its plugin registry is briefly unreachable now retries instead of giving up for the lifetime of that instance — so a momentary network hiccup no longer leaves installed plugins showing an old version until the next restart.