Function buffer_count 

pub fn buffer_count(
    core: &Core,
    binding: &Arc<dyn ProducerBinding>,
    source: NodeId,
    count: usize,
    pack_fn_id: FnId,
) -> NodeId

Fixed-size buffer. Accumulate DATA handles; emit packed array every count items.

• Source DATA: retain + push. When buf.len() == count, pack + emit + clear.
• Source COMPLETE: flush remainder (may be < count), then complete.
• Source ERROR: terminate, release buffered.

Panics

Panics if count is 0.