Every scenario runs through scripts/qa-strict-harness.mjs: each page, frame and worker gets an ordered block list before it runs (paid hosts and routes first, then only the preview, declared fixtures, keyless probes and cached free tile hosts), switches with real input on the picker, and records its assertions per layer and engine. The runner reads the catalog from the live page, fails any layer without an assertion on either engine, can build and serve a keyless checkout itself, and adds rapid, hidden-tab, context-loss, failure-injection, cold-chunk and soak scenarios. The main chunk gets a 1% size budget.
A picked engine now lives in the switch until it runs; only then is the
address written, so a pick superseded by Back or one that fails rewrites no
entry. An engine-changing history visit holds the outgoing share link, which
neither restores nor writes the visited entry, and the running engine takes
the address back once the switch settles, restoring any entry visited while
it was held or not yet listening. Handed-off layers keep running where the
incoming address agrees with the outgoing one and follow a visited entry
where it differs. A failed recovery keeps the error on the loading screen
with an engine picker for a retry, and a failing reveal of the new globe no
longer blocks the cover removal or later requests.
The engine switch moves out of main.js into src/standalone/engineSwitch.js: every
engine change in the page hands the session off (layers, Director, Contacts,
directions and satellite cameras), whether it came from the picker or from
history. Each attempt has a generation; a failure rolls back to the last engine
that started, requests made during a switch or recovery are reconciled once it
settles, and a picked engine adds its history entry only after it starts. The
first-frame wait only lifts the cover and never fails a started engine; a
hidden tab does not wait. Nothing starts after pagehide, and a failed recovery
leaves the picker usable.
German Khokhlov