Add bounded stdin to owner execution

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a06def-6490-7033-8448-2eab2d12ed44

src/sandboxer/core/manager.py

@@ -231,6 +231,8 @@ class SandboxManager:
         command_size = sum(len(arg.encode("utf-8")) for arg in request.command)
         if command_size > 65_536:
             raise ValueError("command argument vector exceeds 65536 bytes")
+        if request.stdin_text is not None and len(request.stdin_text.encode("utf-8")) > 1_000_000:
+            raise ValueError("command stdin exceeds 1000000 bytes")
         invalid_refs = [
             ref
             for ref in request.credential_route_refs
@@ -304,6 +306,7 @@ class SandboxManager:
                 execution_context=context,
                 timeout_seconds=request.timeout_seconds,
                 max_output_bytes=request.max_output_bytes,
+                stdin_text=request.stdin_text,
             )
         except Exception as exc:
             status.state = SandboxState.READY