feat(box): add host workspace mounting and sandbox_exec guidance

src/langbot/pkg/provider/runners/localagent.py

@@ -29,7 +29,13 @@ SANDBOX_EXEC_SYSTEM_GUIDANCE = (
     'When sandbox_exec is available, use it for exact calculations, statistics, structured data parsing, '
     'and code execution instead of estimating mentally. If the user provides numbers, tables, CSV-like text, '
     'JSON, or other data and asks for a computed answer, prefer running a short Python script in sandbox_exec '
-    'and then answer from the tool result.'
+    'and then answer from the tool result. Unless the user explicitly asks for the script, code, or implementation '
+    'details, do not include the generated script in the final answer; return the result and a brief explanation only.'
+)
+SANDBOX_EXEC_WORKSPACE_GUIDANCE = (
+    'A default host workspace is mounted at /workspace for file tasks. When the user asks to read, create, or '
+    'modify local files in the working directory, use sandbox_exec with /workspace paths directly; do not ask the '
+    'user for sandbox parameters such as host_path unless they explicitly need a different directory.'
 )
 
 
@@ -37,6 +43,15 @@ SANDBOX_EXEC_SYSTEM_GUIDANCE = (
 class LocalAgentRunner(runner.RequestRunner):
     """Local agent request runner"""
 
+    def _build_sandbox_system_guidance(self) -> str:
+        guidance = SANDBOX_EXEC_SYSTEM_GUIDANCE
+        default_host_workspace = str(
+            getattr(getattr(self.ap, 'instance_config', None), 'data', {}).get('box', {}).get('default_host_workspace', '')
+        ).strip()
+        if default_host_workspace:
+            guidance = f'{guidance} {SANDBOX_EXEC_WORKSPACE_GUIDANCE}'
+        return guidance
+
     def _build_request_messages(
         self,
         query: pipeline_query.Query,
@@ -48,7 +63,7 @@ class LocalAgentRunner(runner.RequestRunner):
             req_messages.append(
                 provider_message.Message(
                     role='system',
-                    content=SANDBOX_EXEC_SYSTEM_GUIDANCE,
+                    content=self._build_sandbox_system_guidance(),
                 )
             )