diff --git a/agents/s09_agent_teams.py b/agents/s09_agent_teams.py
index 284a1ac19..5f235ce34 100644
--- a/agents/s09_agent_teams.py
+++ b/agents/s09_agent_teams.py
@@ -78,6 +78,7 @@ class MessageBus:
     def __init__(self, inbox_dir: Path):
         self.dir = inbox_dir
         self.dir.mkdir(parents=True, exist_ok=True)
+        self._lock = threading.Lock()
 
     def send(self, sender: str, to: str, content: str,
              msg_type: str = "message", extra: dict = None) -> str:
@@ -92,19 +93,26 @@ def send(self, sender: str, to: str, content: str,
         if extra:
             msg.update(extra)
         inbox_path = self.dir / f"{to}.jsonl"
-        with open(inbox_path, "a") as f:
-            f.write(json.dumps(msg) + "\n")
+        with self._lock:
+            with open(inbox_path, "a") as f:
+                f.write(json.dumps(msg) + "\n")
         return f"Sent {msg_type} to {to}"
 
     def read_inbox(self, name: str) -> list:
         inbox_path = self.dir / f"{name}.jsonl"
         if not inbox_path.exists():
             return []
+        with self._lock:
+            content = inbox_path.read_text()
+            inbox_path.write_text("")
         messages = []
-        for line in inbox_path.read_text().strip().splitlines():
+        for line in content.splitlines():
+            line = line.strip()
             if line:
-                messages.append(json.loads(line))
-        inbox_path.write_text("")
+                try:
+                    messages.append(json.loads(line))
+                except json.JSONDecodeError:
+                    pass
         return messages
 
     def broadcast(self, sender: str, content: str, teammates: list) -> str:
diff --git a/agents/s10_team_protocols.py b/agents/s10_team_protocols.py
index 21f936df3..1bef669a5 100644
--- a/agents/s10_team_protocols.py
+++ b/agents/s10_team_protocols.py
@@ -88,6 +88,7 @@ class MessageBus:
     def __init__(self, inbox_dir: Path):
         self.dir = inbox_dir
         self.dir.mkdir(parents=True, exist_ok=True)
+        self._lock = threading.Lock()
 
     def send(self, sender: str, to: str, content: str,
              msg_type: str = "message", extra: dict = None) -> str:
@@ -102,19 +103,26 @@ def send(self, sender: str, to: str, content: str,
         if extra:
             msg.update(extra)
         inbox_path = self.dir / f"{to}.jsonl"
-        with open(inbox_path, "a") as f:
-            f.write(json.dumps(msg) + "\n")
+        with self._lock:
+            with open(inbox_path, "a") as f:
+                f.write(json.dumps(msg) + "\n")
         return f"Sent {msg_type} to {to}"
 
     def read_inbox(self, name: str) -> list:
         inbox_path = self.dir / f"{name}.jsonl"
         if not inbox_path.exists():
             return []
+        with self._lock:
+            content = inbox_path.read_text()
+            inbox_path.write_text("")
         messages = []
-        for line in inbox_path.read_text().strip().splitlines():
+        for line in content.splitlines():
+            line = line.strip()
             if line:
-                messages.append(json.loads(line))
-        inbox_path.write_text("")
+                try:
+                    messages.append(json.loads(line))
+                except json.JSONDecodeError:
+                    pass
         return messages
 
     def broadcast(self, sender: str, content: str, teammates: list) -> str:
diff --git a/agents/s11_autonomous_agents.py b/agents/s11_autonomous_agents.py
index 856bc92c3..44a024022 100644
--- a/agents/s11_autonomous_agents.py
+++ b/agents/s11_autonomous_agents.py
@@ -81,6 +81,7 @@ class MessageBus:
     def __init__(self, inbox_dir: Path):
         self.dir = inbox_dir
         self.dir.mkdir(parents=True, exist_ok=True)
+        self._lock = threading.Lock()
 
     def send(self, sender: str, to: str, content: str,
              msg_type: str = "message", extra: dict = None) -> str:
@@ -95,19 +96,26 @@ def send(self, sender: str, to: str, content: str,
         if extra:
             msg.update(extra)
         inbox_path = self.dir / f"{to}.jsonl"
-        with open(inbox_path, "a") as f:
-            f.write(json.dumps(msg) + "\n")
+        with self._lock:
+            with open(inbox_path, "a") as f:
+                f.write(json.dumps(msg) + "\n")
         return f"Sent {msg_type} to {to}"
 
     def read_inbox(self, name: str) -> list:
         inbox_path = self.dir / f"{name}.jsonl"
         if not inbox_path.exists():
             return []
+        with self._lock:
+            content = inbox_path.read_text()
+            inbox_path.write_text("")
         messages = []
-        for line in inbox_path.read_text().strip().splitlines():
+        for line in content.splitlines():
+            line = line.strip()
             if line:
-                messages.append(json.loads(line))
-        inbox_path.write_text("")
+                try:
+                    messages.append(json.loads(line))
+                except json.JSONDecodeError:
+                    pass
         return messages
 
     def broadcast(self, sender: str, content: str, teammates: list) -> str:
diff --git a/agents/s_full.py b/agents/s_full.py
index d4dcfd3c6..1a094801c 100644
--- a/agents/s_full.py
+++ b/agents/s_full.py
@@ -364,21 +364,33 @@ def drain(self) -> list:
 class MessageBus:
     def __init__(self):
         INBOX_DIR.mkdir(parents=True, exist_ok=True)
+        self._lock = threading.Lock()
 
     def send(self, sender: str, to: str, content: str,
              msg_type: str = "message", extra: dict = None) -> str:
         msg = {"type": msg_type, "from": sender, "content": content,
                "timestamp": time.time()}
         if extra: msg.update(extra)
-        with open(INBOX_DIR / f"{to}.jsonl", "a") as f:
-            f.write(json.dumps(msg) + "\n")
+        with self._lock:
+            with open(INBOX_DIR / f"{to}.jsonl", "a") as f:
+                f.write(json.dumps(msg) + "\n")
         return f"Sent {msg_type} to {to}"
 
     def read_inbox(self, name: str) -> list:
         path = INBOX_DIR / f"{name}.jsonl"
-        if not path.exists(): return []
-        msgs = [json.loads(l) for l in path.read_text().strip().splitlines() if l]
-        path.write_text("")
+        if not path.exists():
+            return []
+        with self._lock:
+            content = path.read_text()
+            path.write_text("")
+        msgs = []
+        for l in content.splitlines():
+            l = l.strip()
+            if l:
+                try:
+                    msgs.append(json.loads(l))
+                except json.JSONDecodeError:
+                    pass
         return msgs
 
     def broadcast(self, sender: str, content: str, names: list) -> str: