Phase 5: Storage fuzz tests + WAL entryCount fix + SSTable overflow checks + compaction sizeBytes accuracy

- WAL: entryCount is now accurate after restart by counting existing entries
- LSM writeSSTable: adds uint32 overflow checks for key/value/entry counts
- Compaction: sizeBytes now uses actual file size instead of rough guess
- Fuzz tests: 14 new tests covering WAL truncation, LSM put/get/delete,
  recovery, scan, overwrites, SSTable roundtrip, corruption, tombstones

src/barabadb/storage/compaction.nim

@@ -107,13 +107,16 @@ proc compact*(cs: CompactionStrategy, level: int): CompactionResult =
   let outputPath = cs.dataDir / "sstables" / ("level_" & $level & "_" & $tables[0].createdAt & ".sst")
   var sst = writeSSTable(final, outputPath, level + 1)
 
+  # Use actual file size instead of rough guess
+  let actualSize = try: getFileSize(outputPath) except: final.len * 64
+
   let outputMeta = SSTableMeta(
     path: outputPath,
     level: level + 1,
     minKey: sst.minKey,
     maxKey: sst.maxKey,
     entryCount: final.len,
-    sizeBytes: final.len * 64,
+    sizeBytes: actualSize,
     createdAt: tables[^1].createdAt,
   )
 

src/barabadb/storage/lsm.nim

@@ -135,6 +135,8 @@ proc writeSSTable*(entries: seq[Entry], path: string, level: int): SSTable =
   # Write header
   s.write(SSTableMagic)
   s.write(SSTableVersion)
+  if entries.len > high(uint32).int:
+    raise newException(ValueError, "SSTable entry count exceeds uint32 limit")
   s.write(uint32(entries.len))
   s.write(uint32(level))
   let indexOffsetPos = s.getPosition()
@@ -146,8 +148,12 @@ proc writeSSTable*(entries: seq[Entry], path: string, level: int): SSTable =
   var offsets = newSeq[(string, int64)](entries.len)
   for i, entry in entries:
     offsets[i] = (entry.key, int64(s.getPosition()))
+    if entry.key.len > high(uint32).int:
+      raise newException(ValueError, "SSTable key length exceeds uint32 limit")
     s.write(uint32(entry.key.len))
     s.write(entry.key)
+    if entry.value.len > high(uint32).int:
+      raise newException(ValueError, "SSTable value length exceeds uint32 limit")
     s.write(uint32(entry.value.len))
     if entry.value.len > 0:
       s.writeData(addr entry.value[0], entry.value.len)

src/barabadb/storage/wal.nim

@@ -26,6 +26,8 @@ type
     entryCount: uint64
     syncOnWrite: bool
 
+proc readEntries*(walPath: string, untilTimestamp: uint64 = 0): seq[WalEntry]
+
 proc newWriteAheadLog*(dir: string, syncOnWrite: bool = true): WriteAheadLog =
   createDir(dir)
   let path = dir / "wal.log"
@@ -38,9 +40,13 @@ proc newWriteAheadLog*(dir: string, syncOnWrite: bool = true): WriteAheadLog =
     stream.write(WALMagic)
     stream.write(WALVersion)
     stream.flush()
-  # NOTE: entryCount is reset to 0 when appending to existing WAL.
-  # For an accurate count, call readEntries() after construction.
-  WriteAheadLog(path: path, stream: stream, entryCount: 0, syncOnWrite: syncOnWrite)
+  # Count existing entries when appending to an existing WAL so
+  # entryCount() remains accurate across restarts.
+  var count: uint64 = 0
+  if exists and not isEmpty:
+    for e in readEntries(path):
+      inc count
+  WriteAheadLog(path: path, stream: stream, entryCount: count, syncOnWrite: syncOnWrite)
 
 proc writeEntry*(wal: var WriteAheadLog, entry: WalEntry) =
   wal.stream.write(uint8(entry.kind))