Constant LAST_ERROR_TAIL_BYTES 

const LAST_ERROR_TAIL_BYTES: i64 = 8192;

Bounded tail window read from a block’s own persisted output file when looking for a trailing error_during_execution frame — see last_error_frame. Large enough to comfortably hold the frame itself (a single JSON line, typically well under 1KB) plus whatever partial line/chunking noise might precede it; small enough to stay O(1) and not turn muxspect into a log-walker (that’s muxlog’s job, not this tool’s — see the tool’s own design spec §1).