Bug: follow mode unconditionally saves payload files regardless of --save flag

[eigmax]

Description

In examples/keeper/host/src/main.rs:256, the follow-mode loop passes save_only || true to fetch_one, which always evaluates to true. This means every processed block writes a <block>_payload.rlp file to disk, even when --save was not specified.

let (_, data) = fetch_one(rpc_url, &block_tag, save_only || true);

Expected behavior

When --follow is used without --save, payload files should not be saved to disk. The call should pass save_only instead of save_only || true.

Impact

Long-running followers accumulate .rlp files on disk, which can fill storage over time. This also changes the CLI contract — users expect --save to control file persistence.

Suggested fix

let (_, data) = fetch_one(rpc_url, &block_tag, save_only);

Found by Codex code review.