[Bug] Light node can appear healthy without verifiable proof of data availability sampling

[maslitti]

Summary

An Avail light node can report a healthy and running status while there is no clear or verifiable indication that data availability sampling is actively being performed.

This makes it difficult for operators to determine whether their node is effectively contributing to data availability verification.

---

Expected behavior

When a light node is running and marked as healthy, operators should be able to verify that:

• data availability sampling is actively occurring
• the node is successfully participating in DA verification
• participation can be confirmed through observable signals

This may include:

• explicit sampling success metrics
• API endpoints exposing DA verification status
• standardized logs confirming active sampling activity

---

Actual behavior

Even when the node is fully operational:

• the process remains running
• health checks report OK
• network connectivity appears normal

However:

• no metrics indicate sampling success
• no API endpoints expose DA participation status
• no logs confirm that data availability sampling is occurring

As a result, the node can appear healthy while actual data availability samp

[vbhattaccmu]

Hi @maslitti, thanks for the issue. To mitigate this issue we have added an API to track verified cell count per block number.
The endpoint can be accessed here by running the client from main on any public Avail network.

GET /v2/blocks/{block-number}/cell-count

If the verified cell count is available (greater than zero), the response is:

{
  "block_number": {block-number},
  "cell_count": {cell-count}
}

block_number - the block number for which the cell count is requested
cell_count - the number of cells that have been successfully sampled and verified for this block

If the verified cell count is zero or not available (sampling has not completed for this block), the response is:

{
  "error": "Verified cell count is not available; sampling has not completed for this block"
}

Also we log an error if verified count is less than required sampling count on logs.

if required > verified {
    error!(
	block_number,
	unverified_cells = unverified,
	event_type = "CELL_FETCH_INSUFFICIENT",
	"Failed to fetch sufficient cells for block verification"
    );
    return Ok(BlockProcessed::Skipped { block_number });
}

You may need to toggle error type on config's log level here to view the error. I hope this helps.

log_level = "error"
# Light client HTTP server host name (default: 127.0.0.1)
http_server_host = "127.0.0.1"