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/deadlock.nim

@@ -1,7 +1,6 @@
 ## Deadlock Detection — wait-for graph
 import std/tables
 import std/sets
-import std/algorithm
 import std/locks
 
 type
@@ -68,32 +67,25 @@ proc removeTxn*(dd: DeadlockDetector, txnId: uint64) =
 proc detectCycleUnsafe(dd: DeadlockDetector): seq[uint64] =
   var visited = initHashSet[uint64]()
   var inStack = initHashSet[uint64]()
-  var parent = initTable[uint64, uint64]()
 
-  proc dfs(node: uint64): seq[uint64] =
+  proc dfs(node: uint64, path: seq[uint64]): seq[uint64] =
     visited.incl(node)
     inStack.incl(node)
+    var newPath = path & @[node]
     for neighbor in dd.adjacency.getOrDefault(node, @[]):
       if neighbor in inStack:
-        # Found cycle — reconstruct
-        var cycle = @[neighbor, node]
-        var current = node
-        while parent.getOrDefault(current, 0'u64) != neighbor and
-              parent.getOrDefault(current, 0'u64) != 0:
-          current = parent[current]
-          if current == 0: break
-          cycle.add(current)
-        # Verify we actually closed the cycle back to neighbor
-        if cycle[^1] != neighbor and parent.getOrDefault(cycle[^1], 0'u64) == neighbor:
-          cycle.add(neighbor)
-        elif cycle[^1] != neighbor:
-          # Incomplete cycle — should not happen with valid parent chain
-          return @[]
-        cycle.reverse()
+        # Found cycle — reconstruct from path
+        var cycle: seq[uint64] = @[]
+        var found = false
+        for n in newPath:
+          if n == neighbor:
+            found = true
+          if found:
+            cycle.add(n)
+        cycle.add(neighbor)
         return cycle
       if neighbor notin visited:
-        parent[neighbor] = node
-        let cycle = dfs(neighbor)
+        let cycle = dfs(neighbor, newPath)
         if cycle.len > 0:
           return cycle
     inStack.excl(node)
@@ -101,7 +93,7 @@ proc detectCycleUnsafe(dd: DeadlockDetector): seq[uint64] =
 
   for txnId in dd.txnIds:
     if txnId notin visited:
-      let cycle = dfs(txnId)
+      let cycle = dfs(txnId, @[])
       if cycle.len > 0:
         return cycle
   return @[]

src/barabadb/core/gossip.nim

@@ -75,6 +75,9 @@ proc serialize*(msg: GossipMessage): seq[byte] =
   s.close()
 
 proc deserializeGossipMessage*(data: seq[byte]): GossipMessage =
+  const MaxGossipIdLen = 256
+  const MaxGossipNodeCount = 4096
+  const MaxGossipHostLen = 256
   let s = newStringStream(cast[string](data))
   let magic = s.readStr(4)
   if magic != GossipMagic:
@@ -83,16 +86,24 @@ proc deserializeGossipMessage*(data: seq[byte]): GossipMessage =
   if version != GossipProtoVersion:
     raise newException(ValueError, "Unsupported gossip protocol version")
   let senderIdLen = int(s.readUint32())
+  if senderIdLen > MaxGossipIdLen:
+    raise newException(ValueError, "Gossip senderId too long")
   result.senderId = if senderIdLen > 0: s.readStr(senderIdLen) else: ""
   result.senderIncarnation = s.readUint64()
   let nodeCount = int(s.readUint32())
+  if nodeCount > MaxGossipNodeCount:
+    raise newException(ValueError, "Gossip node count too large")
   result.nodes = newSeq[(string, NodeState, uint64, string, int)](nodeCount)
   for i in 0 ..< nodeCount:
     let idLen = int(s.readUint32())
+    if idLen > MaxGossipIdLen:
+      raise newException(ValueError, "Gossip node id too long")
     let id = if idLen > 0: s.readStr(idLen) else: ""
     let state = NodeState(s.readUint32())
     let incarnation = s.readUint64()
     let hostLen = int(s.readUint32())
+    if hostLen > MaxGossipHostLen:
+      raise newException(ValueError, "Gossip host too long")
     let host = if hostLen > 0: s.readStr(hostLen) else: ""
     let port = int(s.readUint32())
     result.nodes[i] = (id, state, incarnation, host, port)

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: