[thdxr]

when an execute was stopped (caller disconnect, timeout, toolbar stop) while page.goto waited on a server that hadn't answered, chromium kept Page.navigate in flight on the tab and queued every renderer-bound command behind it. the next execute's connectOverCDP timed out after 15s, the stop path's own commands hit the 60s extension timeout, and only closing the tab recovered.

the fix:

• on stop the relay sends Page.stopLoading to the session's tabs (handled browser-side, so it answers while the navigation is pending) before closing the script's browser connection (cli/src/relay.ts onStoppingExecute hook, cli/src/session-manager.ts endStoppedScript).
• the per-call timeout is now armed before the session's execute lock, so a call queued behind a stopped execute that is still settling answers within its own --timeout-ms (cli/src/session-manager/execution.ts).
• tests: cli/test/session-manager.test.ts (stop and timeout cancel navigation before abort; a queued call honours its timeout), cli/test/execute-realm-browser.ts (headless chromium: stop during a never-answering goto, next return 1 works fast).

verified end to end with headless chromium: before, the next execute after a killed caller never answered (gave up at 45s); after, ~110ms.

fixes #238