SessionV2 durable execution and monotonic state

SessionV2.prompt() durably admits exactly one session_input row before advisory SessionExecution.wake(sessionID); resume:false is admit-only. The serialized runner promotes inbox rows into visible user messages and makes one explicit llm.stream(request) call per provider turn after reloading projected history; never bridge through legacy SessionPrompt.loop(...). Preserve project isolation and persist matching, parent-child, replay, and stable session identity so restarts do not change behavior. Session-state writes must reject or ignore stale turn completions rather than use last-writer-wins; identity must not depend on counters or timestamps. Keep frozen prompt/LTM bytes and persisted delta positions cache-stable, bound or coalesce updates, and safely default malformed persisted values.