Function run_checkpoint_task 

pub async fn run_checkpoint_task(
    pool: Arc<ConnectionPool>,
    config: CheckpointConfig,
    event_store: Option<Arc<dyn EventStore>>,
    namespace: String,
    shutdown_rx: Receiver<()>,
)

Run the WAL checkpoint background task.

Long-running async task — spawn with tokio::spawn. Loops until shutdown_rx observes a change (or its sender is dropped). Callers MUST hold the paired tokio::sync::watch::Sender for the daemon’s run scope and send on it to shut down — do NOT rely on pool’s Arc refcount reaching zero; a sibling owner (e.g. event_store) holding its own clone makes that check unreachable (issue #774).

Issues PRAGMA wal_checkpoint(PASSIVE) every tick via try_writer_nowait (zero-wait try-lock): a busy writer skips the tick rather than stalling write traffic. A WARNING fires once per below→above threshold crossing, not every tick.

event_store (ADR-094): when Some, appends a best-effort CheckpointOutcomeRecorded event on every at/above-warn_pages tick, plus one drain row when pressure falls back below warn_pages. None is a no-op. See crates/khive-db/docs/api/checkpoint.md for the full shutdown-mechanism and event-emission design history.