Storage hardening: btree size fix, WAL entryCount note, LSM put error handling

- btree.nim: insertNonFull returns bool; size only increments for new keys
- wal.nim: comment about entryCount reset on append
- lsm.nim: recovery/put/delete/putUnsafe raise IOError if put fails after flush

src/barabadb/storage/btree.nim

@@ -69,16 +69,18 @@ proc splitChild[K, V](parent: BTreeNode[K, V], index: int, order: int) =
   else:
     child.keys.setLen(mid)
 
-proc insertNonFull[K, V](node: BTreeNode[K, V], key: K, value: V, order: int) =
+proc insertNonFull[K, V](node: BTreeNode[K, V], key: K, value: V, order: int): bool =
+  ## Returns true if a new key was inserted, false if existing key got a new value.
   var i = node.keys.len - 1
   if node.isLeaf:
     while i >= 0 and key < node.keys[i]:
       dec i
     if i >= 0 and key == node.keys[i]:
       node.values[i].add(value)
-      return
+      return false
     node.keys.insert(key, i + 1)
     node.values.insert(@[value], i + 1)
+    return true
   else:
     while i >= 0 and key < node.keys[i]:
       dec i
@@ -87,19 +89,21 @@ proc insertNonFull[K, V](node: BTreeNode[K, V], key: K, value: V, order: int) =
       splitChild(node, i, order)
       if key > node.keys[i]:
         inc i
-    insertNonFull(node.children[i], key, value, order)
+    return insertNonFull(node.children[i], key, value, order)
 
 proc insert*[K, V](btree: var BTreeIndex[K, V], key: K, value: V) =
   acquire(btree.lock)
   try:
+    var inserted = false
     if btree.root.keys.len == btree.order - 1:
       var newRoot = newBTreeNode[K, V](isLeaf = false)
       newRoot.children.add(btree.root)
       splitChild(newRoot, 0, btree.order)
       btree.root = newRoot
-      insertNonFull(btree.root, key, value, btree.order)
+      inserted = insertNonFull(btree.root, key, value, btree.order)
     else:
-      insertNonFull(btree.root, key, value, btree.order)
+      inserted = insertNonFull(btree.root, key, value, btree.order)
+    if inserted:
       inc btree.size
   finally:
     release(btree.lock)

src/barabadb/storage/lsm.nim

@@ -375,11 +375,13 @@ proc newLSMTree*(dir: string, memMaxSize: int = DefaultMemTableSize): LSMTree =
               of wekPut:
                 if not result.memTable.put(key, value, timestamp):
                   result.flushUnsafe()
-                  discard result.memTable.put(key, value, timestamp)
+                  if not result.memTable.put(key, value, timestamp):
+                    raise newException(IOError, "WAL recovery: failed to insert key into memtable")
               of wekDelete:
                 if not result.memTable.put(key, @[], timestamp, deleted = true):
                   result.flushUnsafe()
-                  discard result.memTable.put(key, @[], timestamp, deleted = true)
+                  if not result.memTable.put(key, @[], timestamp, deleted = true):
+                    raise newException(IOError, "WAL recovery: failed to insert delete tombstone into memtable")
               of wekCommit:
                 discard
               of wekCheckpoint:
@@ -401,7 +403,8 @@ proc put*(db: LSMTree, key: string, value: seq[byte]) =
       db.flushUnsafe()
     db.immutableMem = db.memTable
     db.memTable = newMemTable(db.memMaxSize)
-    discard db.memTable.put(key, value, ts)
+    if not db.memTable.put(key, value, ts):
+      raise newException(IOError, "LSM put failed after flush")
 
 proc delete*(db: LSMTree, key: string) =
   let ts = uint64(getMonoTime().ticks())
@@ -416,7 +419,8 @@ proc delete*(db: LSMTree, key: string) =
       db.flushUnsafe()
     db.immutableMem = db.memTable
     db.memTable = newMemTable(db.memMaxSize)
-    discard db.memTable.put(key, @[], ts, deleted = true)
+    if not db.memTable.put(key, @[], ts, deleted = true):
+      raise newException(IOError, "LSM delete failed after flush")
 
 proc putUnsafe*(db: LSMTree, key: string, value: seq[byte], deleted: bool = false) =
   ## Direct LSM insert without WAL logging — used by recovery.
@@ -428,7 +432,8 @@ proc putUnsafe*(db: LSMTree, key: string, value: seq[byte], deleted: bool = fals
       db.flushUnsafe()
     db.immutableMem = db.memTable
     db.memTable = newMemTable(db.memMaxSize)
-    discard db.memTable.put(key, value, ts, deleted)
+    if not db.memTable.put(key, value, ts, deleted):
+      raise newException(IOError, "LSM putUnsafe failed after flush")
 
 proc deleteUnsafe*(db: LSMTree, key: string) =
   putUnsafe(db, key, @[], deleted = true)

src/barabadb/storage/wal.nim

@@ -38,6 +38,8 @@ 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)
 
 proc writeEntry*(wal: var WriteAheadLog, entry: WalEntry) =