address review: charge the escaped batch reply against the budget

crates/mcp/src/tools.rs

@@ -369,12 +369,14 @@ pub fn call_tool(b: &mut dyn Backend, name: &str, a: &Value) -> ToolResult {
                 let id = c.get("command").and_then(Value::as_str).unwrap_or("");
                 match exec(b, id, c.get("params").cloned().unwrap_or(json!({}))) {
                     Ok(v) => {
-                        used = used.saturating_add(v.to_string().len());
+                        let entry = json!({"command": id, "ok": true, "result": v});
+                        // What the reply carries: the entry as text, escaped again inside the JSON-RPC reply.
+                        used = used.saturating_add(json!(entry.to_string()).to_string().len());
                         if used > MAX_BATCH_BYTES {
                             out.push(json!({"command": id, "ok": false, "error": "the batch's results passed 64 MiB; stopped here"}));
                             return ToolResult { content: vec![json!({"type": "text", "text": Value::Array(out).to_string()})], is_error: true };
                         }
-                        out.push(json!({"command": id, "ok": true, "result": v}));
+                        out.push(entry);
                     }
                     Err(e) => {
                         out.push(json!({"command": id, "ok": false, "error": e}));

crates/mcp/tests/it/batch_budget.rs

@@ -43,3 +43,16 @@ fn the_batch_tool_is_bounded_in_commands_and_result_bytes() {
     assert!(err && text.contains("64 MiB"), "{}", &text[text.len().saturating_sub(200)..]);
     assert!(text.len() < (64 << 20) + (4 << 20));
 }
+
+#[test]
+fn the_batch_tool_charges_the_escaped_reply() {
+    // Quotes escape twice on the way out (`\\\"`), so 30 results of ~2 MiB serialize to ~120 MiB.
+    let mut server = Server::new(Box::new(Headless::with_document()));
+    let notes = json!({"jsonrpc": "2.0", "id": 1, "method": "tools/call", "params": {"name": "run_command", "arguments": {"command": "slide.notes", "params": {"text": "\"".repeat(1 << 20)}}}});
+    server.handle_line(&notes.to_string()).unwrap();
+    let commands = vec![json!({"command": "slide.inspect"}); 30];
+    let line = json!({"jsonrpc": "2.0", "id": 2, "method": "tools/call", "params": {"name": "batch", "arguments": {"commands": commands, "keepGoing": true}}});
+    let reply = server.handle_line(&line.to_string()).unwrap();
+    assert!(reply.len() < (64 << 20) + (4 << 20), "{} bytes", reply.len());
+    assert!(reply.contains("64 MiB"));
+}