Function spawn 

pub fn spawn(
    pool: &ConnectionPool,
    capacity: usize,
) -> Result<WriterTaskHandle, SqliteError>

Spawn the write-owner task (ADR-067 Component A) on the current Tokio runtime.

Opens a dedicated standalone writer connection independent of the pool’s Mutex-guarded writer() connection used by unmigrated paths. That one-time infrastructure open is uncounted; every dequeued top-level request or successful BEGIN IMMEDIATE increments the writer-task acquisition class. Returns the cloneable WriterTaskHandle sender half. The task normally runs until every handle clone is dropped and the channel closes; a request panic, failed rollback, or poisoned connection puts it into the permanent terminal state documented below.

capacity bounds the channel (PoolConfig::write_queue_capacity / KHIVE_WRITE_QUEUE_CAPACITY, ADR-067 recommends 256).

Errors

Must be called from within a Tokio runtime context (calls tokio::spawn). Returns an error if the pool cannot open a standalone writer connection (e.g. an in-memory pool has no standalone-connection support). See crates/khive-db/docs/api/writer-task.md for the migration-slice scope this commits per BEGIN IMMEDIATE.