ROOT CAUSE of per-session command drift on the extension path: the daemon's
liveness check (`is_connection_alive` → `Browser.getVersion`) is a BROWSER-level
command. The relay only answered Target.* locally and forwarded the rest, so
Browser.getVersion went to the extension, which can only do per-tab
chrome.debugger → it errored → CdpClient saw TransportError → connection deemed
DEAD → the daemon closed + reconnected + re-ran discover_and_attach_targets on
EVERY command. Each re-discover rebuilds pages from the relay's minimal
targetInfo and resets active_page_index=0, so eval/get-title/screenshot drifted
to the first tab (about:blank / a foreign focused tab).
Reproduced locally (throwaway Chrome + Extensions.loadUnpacked + fork.24 nm-host):
trace showed discover_and_attach_targets running on every command (pages
before=0) and [ev] active_idx reset to 0.
Fix: relay answers Browser.getVersion locally with a stub version (like
getTargets), so the liveness probe succeeds → connection stays alive → no
reconnect/re-discover → the session's active tab is preserved. Pairs with
fork.24's add_background_page. relay.rs: 10 unit tests.