[wieslawsoltes]

VS Code schedules its immediate shutdown storage flush from beforeunload, then disposes and cancels that timer from pagehide. WebScene dispatched both events synchronously, so freshly accepted MCP secrets never reached IndexedDB before reload.

This splits the terminal lifecycle at the existing bounded #878 persistence boundary: veto-capable beforeunload remains synchronous, its zero-delay/IndexedDB lineage drains, pagehide runs once as the next browser task, and the terminal host request follows only after bounded descendants complete. Delayed timers, intervals, rAF, unrelated work, and tasks beyond the 1,024-task budget remain excluded.

Closes #880.

Validation:

• webscene_native_terminal_indexeddb_navigation: 1/1 passed in 1.21 seconds
• regression order: beforeunload,flush-timer,commit,continuation,pagehide
• restarted engine reads the committed value
• the retained self-refilling lifecycle test consumes the bounded budget and cannot starve navigation