fix(common): make defaultMaxBlobSizeStr a string literal so -ldflags -X works

A previous version initialised the variable via strconv.FormatUint(...),
which Go's linker treats as a non-constant expression — so -ldflags -X
silently no-ops the override. Every benchmark that tried to set a
smaller MaxBlobSize at link time was actually running with the 128 MiB
default, masking what we were measuring.

The correct form is a plain string literal in the source. The Fibre
cap is documented in the comment so the magic number stays
self-explanatory; init() still parses and falls back to the literal
value if parsing fails.

Author: Wondertan

block/internal/common/consts.go

@@ -2,26 +2,29 @@ package common
 
 import "strconv"
 
-// fibreMaxPayload is the maximum payload Fibre will accept in a single
-// blob: protocol max blob size (1 << 27 = 128 MiB) minus the 5-byte
-// Fibre blob header (1 byte version + 4 byte data size). See
-// celestia-app/v9/fibre/blob.go (blobHeaderLen) and fibre/protocol_params.go
-// (MaxBlobSize). Sized to fit a full Fibre blob and nothing more.
-const fibreMaxPayload = (1 << 27) - 5
-
 // defaultMaxBlobSizeStr holds the string representation of the default blob
-// size limit. Override at link time via:
+// size limit. Anchored to Fibre's actual cap: protocol MaxBlobSize
+// (1 << 27 = 128 MiB) minus the 5-byte Fibre blob header (1 byte version +
+// 4 byte data size). See celestia-app/v9/fibre/blob.go (blobHeaderLen)
+// and fibre/protocol_params.go (MaxBlobSize).
+//
+// MUST be a string literal: Go's `-ldflags "-X ..."` only takes effect
+// on variables initialized to a string constant, NOT a function call.
+// A previous version used strconv.FormatUint here, which compiled but
+// silently ignored ldflag overrides.
+//
+// Override at link time via:
 //
-//	go build -ldflags "-X github.com/evstack/ev-node/block/internal/common.defaultMaxBlobSizeStr=125829120"
-var defaultMaxBlobSizeStr = strconv.FormatUint(fibreMaxPayload, 10)
+//	go build -ldflags "-X github.com/evstack/ev-node/block/internal/common.defaultMaxBlobSizeStr=33554432"
+var defaultMaxBlobSizeStr = "134217723" // 1 << 27 - 5 = 128 MiB - 5 B
 
 // DefaultMaxBlobSize is the max blob size limit used for blob submission.
 var DefaultMaxBlobSize uint64
 
 func init() {
 	v, err := strconv.ParseUint(defaultMaxBlobSizeStr, 10, 64)
 	if err != nil || v == 0 {
-		DefaultMaxBlobSize = fibreMaxPayload
+		DefaultMaxBlobSize = 134217723
 		return
 	}
 	DefaultMaxBlobSize = v