Function open_run 

pub fn open_run(
    config: &EventStoreConfig,
    instance_id: &str,
    run_id: RunId,
    parent_run_id: Option<RunId>,
    start_ts_init: UnixNanos,
    components: &RegisteredComponents,
    halt_signal: HaltSignal,
    clock: &'static AtomicTime,
) -> Result<EventStoreSession, BootError>

Opens a fresh run, spawns the writer, and submits a blocking RunStarted entry.

The kernel calls this from start() after components have registered with the trader so the captured RunStarted payload reflects the actual boot configuration. The function blocks until the writer’s high-watermark advances past zero (i.e. the RunStarted entry has durably committed) or until EventStoreConfig::run_started_timeout elapses.

feature_flags is appended after the configured feature_flags so the retention mode survives in the manifest as retention=<mode>.

Errors

Returns an error if the backend rejects open, if the writer rejects the submit, if the commit does not happen inside the configured ceiling, or if the writer fail-stops while waiting for the commit.