diff --git a/haiku_rag_slim/haiku/rag/skills/_tools.py b/haiku_rag_slim/haiku/rag/skills/_tools.py
index 22c17b8b..28821d00 100644
--- a/haiku_rag_slim/haiku/rag/skills/_tools.py
+++ b/haiku_rag_slim/haiku/rag/skills/_tools.py
@@ -240,7 +240,7 @@ def create_skill_tools(
         tools["get_document"] = get_document
 
     if "execute_code" in tool_names:
-        _sandbox: list[Any] = []  # mutable container for closure; holds [Sandbox] or []
+        _sandbox_state: dict[str, Any] = {}  # {run_id, sandbox} — reset per invocation
 
         async def execute_code(ctx: RunContext[SkillRunDeps], code: str) -> str:
             """Execute Python code in a sandboxed interpreter.
@@ -249,7 +249,8 @@ def create_skill_tools(
             and a virtual filesystem at /documents/ with document content and
             structure (metadata.json, content.txt, items.jsonl per document).
 
-            Use print() to output results. Variables persist between calls.
+            Use print() to output results. Variables persist between calls
+            within the same skill invocation.
 
             Args:
                 code: Python code to execute.
@@ -257,15 +258,17 @@ def create_skill_tools(
             from haiku.rag.agents.analysis.dependencies import AnalysisContext
             from haiku.rag.agents.analysis.sandbox import Sandbox
 
-            if not _sandbox:
+            rid = ctx.run_id or ""
+            if _sandbox_state.get("run_id") != rid:
                 state = _get_state(ctx, state_type)
                 doc_filter = state.document_filter if state else None
                 context = AnalysisContext(filter=doc_filter)
-                _sandbox.append(
-                    Sandbox(db_path=db_path, config=config, context=context)
+                _sandbox_state["run_id"] = rid
+                _sandbox_state["sandbox"] = Sandbox(
+                    db_path=db_path, config=config, context=context
                 )
 
-            sandbox = _sandbox[0]
+            sandbox = _sandbox_state["sandbox"]
             result = await sandbox.execute(code)
 
             state = _get_state(ctx, state_type)