Various refactors and test hardening

arbnode/db/schema/schema.go

@@ -15,17 +15,20 @@ var (
 	SequencerBatchMetaPrefix            []byte = []byte("s") // maps a batch sequence number to BatchMetadata
 	DelayedSequencedPrefix              []byte = []byte("a") // maps a delayed message count to the first sequencer batch sequence number with this delayed count
 	MelStatePrefix                      []byte = []byte("l") // maps a parent chain block number to its computed MEL state
-	MelDelayedMessagePrefix             []byte = []byte("y") // maps a delayed sequence number to an accumulator and an RLP encoded message [TODO(NIT-4209): might need to replace or be replaced by RlpDelayedMessagePrefix]
-	MelSequencerBatchMetaPrefix         []byte = []byte("q") // maps a batch sequence number to BatchMetadata [TODO(NIT-4209): might need to replace or be replaced by SequencerBatchMetaPrefix]
+	MelDelayedMessagePrefix             []byte = []byte("y") // maps a delayed sequence number to an RLP-encoded DelayedInboxMessage (coexists with RlpDelayedMessagePrefix for legacy data below the initial MEL boundary)
+	MelSequencerBatchMetaPrefix         []byte = []byte("q") // maps a batch sequence number to BatchMetadata (coexists with SequencerBatchMetaPrefix for legacy data below the initial MEL boundary)
 
-	MessageCountKey             []byte = []byte("_messageCount")                // contains the current message count
-	LastPrunedMessageKey        []byte = []byte("_lastPrunedMessageKey")        // contains the last pruned message key
-	LastPrunedDelayedMessageKey []byte = []byte("_lastPrunedDelayedMessageKey") // contains the last pruned RLP delayed message key
-	DelayedMessageCountKey      []byte = []byte("_delayedMessageCount")         // contains the current delayed message count
-	SequencerBatchCountKey      []byte = []byte("_sequencerBatchCount")         // contains the current sequencer message count
-	DbSchemaVersion             []byte = []byte("_schemaVersion")               // contains a uint64 representing the database schema version
-	HeadMelStateBlockNumKey     []byte = []byte("_headMelStateBlockNum")        // contains the latest computed MEL state's parent chain block number
-	InitialMelStateBlockNumKey  []byte = []byte("_initialMelStateBlockNum")     // contains the initial MEL state's parent chain block number (legacy/MEL boundary)
+	MessageCountKey                     []byte = []byte("_messageCount")                        // contains the current message count
+	LastPrunedMessageKey                []byte = []byte("_lastPrunedMessageKey")                // contains the last pruned message key
+	LastPrunedDelayedMessageKey         []byte = []byte("_lastPrunedDelayedMessageKey")         // contains the last pruned RLP delayed message key
+	LastPrunedLegacyDelayedMessageKey   []byte = []byte("_lastPrunedLegacyDelayedMessageKey")   // contains the last pruned legacy delayed message key
+	LastPrunedMelDelayedMessageKey      []byte = []byte("_lastPrunedMelDelayedMessageKey")      // contains the last pruned MEL delayed message key
+	LastPrunedParentChainBlockNumberKey []byte = []byte("_lastPrunedParentChainBlockNumberKey") // contains the last pruned parent chain block number key
+	DelayedMessageCountKey              []byte = []byte("_delayedMessageCount")                 // contains the current delayed message count
+	SequencerBatchCountKey              []byte = []byte("_sequencerBatchCount")                 // contains the current sequencer message count
+	DbSchemaVersion                     []byte = []byte("_schemaVersion")                       // contains a uint64 representing the database schema version
+	HeadMelStateBlockNumKey             []byte = []byte("_headMelStateBlockNum")                // contains the latest computed MEL state's parent chain block number
+	InitialMelStateBlockNumKey          []byte = []byte("_initialMelStateBlockNum")             // contains the initial MEL state's parent chain block number (legacy/MEL boundary)
 )
 
 const CurrentDbSchemaVersion uint64 = 2

arbnode/db/schema/schema_test.go

@@ -0,0 +1,62 @@
+// Copyright 2026, Offchain Labs, Inc.
+// For license information, see https://github.com/OffchainLabs/nitro/blob/master/LICENSE.md
+package schema
+
+import (
+	"testing"
+)
+
+func TestPrefixUniqueness(t *testing.T) {
+	// All single-byte DB key prefixes must be unique to prevent data corruption.
+	prefixes := []struct {
+		name  string
+		value []byte
+	}{
+		{"MessagePrefix", MessagePrefix},
+		{"BlockHashInputFeedPrefix", BlockHashInputFeedPrefix},
+		{"BlockMetadataInputFeedPrefix", BlockMetadataInputFeedPrefix},
+		{"MissingBlockMetadataInputFeedPrefix", MissingBlockMetadataInputFeedPrefix},
+		{"MessageResultPrefix", MessageResultPrefix},
+		{"LegacyDelayedMessagePrefix", LegacyDelayedMessagePrefix},
+		{"RlpDelayedMessagePrefix", RlpDelayedMessagePrefix},
+		{"ParentChainBlockNumberPrefix", ParentChainBlockNumberPrefix},
+		{"SequencerBatchMetaPrefix", SequencerBatchMetaPrefix},
+		{"DelayedSequencedPrefix", DelayedSequencedPrefix},
+		{"MelStatePrefix", MelStatePrefix},
+		{"MelDelayedMessagePrefix", MelDelayedMessagePrefix},
+		{"MelSequencerBatchMetaPrefix", MelSequencerBatchMetaPrefix},
+	}
+	seen := make(map[string]string) // prefix string → variable name
+	for _, p := range prefixes {
+		key := string(p.value)
+		if existing, ok := seen[key]; ok {
+			t.Fatalf("prefix collision: %s and %s both use %q", existing, p.name, key)
+		}
+		seen[key] = p.name
+	}
+
+	keys := []struct {
+		name  string
+		value []byte
+	}{
+		{"MessageCountKey", MessageCountKey},
+		{"LastPrunedMessageKey", LastPrunedMessageKey},
+		{"LastPrunedDelayedMessageKey", LastPrunedDelayedMessageKey},
+		{"LastPrunedLegacyDelayedMessageKey", LastPrunedLegacyDelayedMessageKey},
+		{"LastPrunedMelDelayedMessageKey", LastPrunedMelDelayedMessageKey},
+		{"LastPrunedParentChainBlockNumberKey", LastPrunedParentChainBlockNumberKey},
+		{"DelayedMessageCountKey", DelayedMessageCountKey},
+		{"SequencerBatchCountKey", SequencerBatchCountKey},
+		{"DbSchemaVersion", DbSchemaVersion},
+		{"HeadMelStateBlockNumKey", HeadMelStateBlockNumKey},
+		{"InitialMelStateBlockNumKey", InitialMelStateBlockNumKey},
+	}
+	seenKeys := make(map[string]string)
+	for _, k := range keys {
+		key := string(k.value)
+		if existing, ok := seenKeys[key]; ok {
+			t.Fatalf("key collision: %s and %s both use %q", existing, k.name, key)
+		}
+		seenKeys[key] = k.name
+	}
+}