Complete plan execution: gossip/raft bounds, deadlock fix, JSON escaping, memtable limits

Remaining plan items:
- 1.4 hybrid_search: JSON built with std/json instead of string concat
- 2.3 lsm.nim: reject oversized memtable entries
- 3.3 gossip.nim: bounds checking for idLen/nodeCount/hostLen
- 3.4 raft.nim: max length caps for cmdLen/dataLen/logLen
- 4.3 deadlock.nim: per-path seq stack instead of global parent table

src/barabadb/core/raft.nim

@@ -115,13 +115,19 @@ proc loadState(node: RaftNode) =
     if votedForLen > 0:
       node.votedFor = s.readStr(votedForLen)
     let logLen = int(s.readUint32())
+    if logLen > 1_000_000:
+      raise newException(ValueError, "Raft log length too large")
     node.log = newSeq[LogEntry](logLen)
     for i in 0..<logLen:
       let term = s.readUint64()
       let index = s.readUint64()
       let cmdLen = int(s.readUint32())
+      if cmdLen > 1_000_000:
+        raise newException(ValueError, "Raft command length too large")
       let cmd = s.readStr(cmdLen)
       let dataLen = int(s.readUint32())
+      if dataLen > 10_000_000:
+        raise newException(ValueError, "Raft data length too large")
       var data = newSeq[byte](dataLen)
       if dataLen > 0:
         if s.readData(addr data[0], dataLen) != dataLen: