diff --git a/.gitignore b/.gitignore
index 6e3390e3a..7d851b760 100644
--- a/.gitignore
+++ b/.gitignore
@@ -146,4 +146,8 @@ data/
 sessions/
 backups/
 uploads/
-config/mcp.json
\ No newline at end of file
+config/mcp.json
+# Local env backups (ignored)
+.env.bak
+.env.bak2
+.env.kai
diff --git a/src/claude/sdk_integration.py b/src/claude/sdk_integration.py
index 5a95f16da..dce9fdd74 100644
--- a/src/claude/sdk_integration.py
+++ b/src/claude/sdk_integration.py
@@ -309,11 +309,15 @@ def _stderr_callback(line: str) -> None:
                     path=str(claude_md_path),
                 )
 
-            # When DISABLE_TOOL_VALIDATION=true, pass None for allowed/disallowed
-            # tools so the SDK does not restrict tool usage (e.g. MCP tools).
+            # When DISABLE_TOOL_VALIDATION=true, pass [] (not None) for
+            # allowed/disallowed tools. claude-agent-sdk subprocess_cli.py
+            # calls list(options.allowed_tools) unconditionally and crashes
+            # with "'NoneType' object is not iterable". Empty list is treated
+            # by the CLI as "no --allowedTools flag" → no restriction, which
+            # is the intent of DISABLE_TOOL_VALIDATION=true.
             if self.config.disable_tool_validation:
-                sdk_allowed_tools = None
-                sdk_disallowed_tools = None
+                sdk_allowed_tools = []
+                sdk_disallowed_tools = []
             else:
                 sdk_allowed_tools = self.config.claude_allowed_tools
                 sdk_disallowed_tools = self.config.claude_disallowed_tools