[model_edit] — Calling with add_block operations — Misleading layout_mode error

[troyp76]

Bug Report

Reporter: agent

Date: 2026-07-24

Severity: High

Reproducibility: Always

---

Summary

The model_edit MCP tool rejects calls containing add_block operations with the error argument "layout_mode" not provided, even though layout_mode is declared as an optional parameter in the tool schema. The error fires unconditionally whenever add_block operations are present, regardless of whether layout_mode was actually supplied. The error message does not indicate that layout_mode is conditionally required.

Expected Behavior

layout_mode should be treated as a truly optional parameter as declared in the tool schema. When layout_mode is provided, the call should proceed to execution. When it is omitted with add_block operations, the tool should either accept the call (using a sensible default) or produce a clear error stating that layout_mode is required for add_block operations specifically.

Actual Behavior

Every call to model_edit that includes add_block operations fails with the error argument "layout_mode" not provided. This happens even when layout_mode is explicitly included in the call. The error message is generic — it does not specify which operation or parameter triggered the requirement, making it impossible to diagnose without trial and error.

When layout_mode is explicitly provided, a different error appears about #ref scoping (#StabilityControlSystem not found), which may be a separate issue or a cascading effect of the parameter validation failing first.

Reproduction Steps

Prerequisites:

• MATLAB R2025b Update 3 with Simulink
• SATK 2026.07.22 installed
• A Simulink model loaded in the current session (e.g., StabilityControlSystem)
• model_read tool available (SATK initialized)

1. Call model_edit with an add_block operation and a ref parameter, without providing layout_mode:

      model_edit(
        model: "StabilityControlSystem",
        scope: "blk_131",
        operations: [{op: "add_block", params: {Position: [50,50,130,90]}, ref: "testblk", type: "Constant", parent: "StabilityControlSystem/VehiclePlant"}]
      )
      
   

   Observe: Error argument "layout_mode" not provided
2. Call model_edit with the same add_block operation but explicitly include layout_mode: "incremental":

      model_edit(
        model: "StabilityControlSystem",
        scope: "blk_131",
        layout_mode: "incremental",
        operations: [{op: "add_block", params: {Position: [50,50,130,90]}, ref: "testblk", type: "Constant", parent: "StabilityControlSystem/VehiclePlant"}]
      )
      
   

   Observe: A different error — #StabilityControlSystem not found — ref/#ref are scoped to a single model_edit call
3. Note that create_subsystem and configure operations succeed without layout_mode, but add_block does not.

Minimal Reproduction

# In any agent session with Simulink MCP tools available:
# Call model_edit with add_block + ref, no layout_mode → "argument layout_mode not provided"
# Call model_edit with add_block + ref + layout_mode → "#ref not found" scoping error

Environment

Toolkit & Agent

Detail	Value
SATK Version	2026.07.22
Agent / Client	Claude Code CLI
Agent Workspace Root	\simulinkTests
MCP Server Mode	attach-to-existing (port 31516)
Available MCP Tools	model_read, model_edit, model_overview, model_query_params, model_resolve_params, model_check, model_read_diagnostics, model_test, model_configure, evaluate_matlab_code, run_matlab_file, run_matlab_test_file, check_matlab_code, detect_matlab_toolboxes

Skills

Skills · 0 ⊘ 0 ▶ 0 ✗ 0

filing-bug-reports · 1

• ⊘ filing-bug-reports
  testing-simulink-models · 1

• ⊘ testing-simulink-models
  ⊘ name-only · ▶ invoked · ✗ unregistered SATK

Skill Conflict Analysis

N/A — fewer than 2 skills with bodies loaded into context

MATLAB

Detail	Value
MATLAB Version	25.2.0.3123386 (R2025b) Update 3
MATLAB Working Directory	C:\simulinkTests
Simulink Version	25.2
Relevant Toolboxes	Simulink 25.2
setup.m Status	N/A
Connector Port	31516

Platform

Detail	Value
OS	Windows 11 Home Version 10.0 (Build 26200)
Architecture	win64

Error Output

argument "layout_mode" not provided

When layout_mode is explicitly provided:

[Autolayout] skip: model=StabilityControlSystem, scope=blk_131, empty_accumulated

ans =

    'status: error
     model: StabilityControlSystem
     scope: blk_131
     error_code: DEPENDENCY_ERROR
     message: #StabilityControlSystem not found — ref/#ref are scoped to a single model_edit call. Use the blk_ID from the previous call's "created" map instead of #StabilityControlSystem.'

Impact

• Scope: All users calling model_edit with add_block operations that use ref for intra-call block referencing.
• Workaround: Unclear. Providing layout_mode changes the error but does not resolve the #ref scoping issue. It is not known whether add_block without ref works without layout_mode.
• Blocking: Blocks building subsystems incrementally — cannot add blocks to a newly created subsystem in a separate model_edit call, which is the natural workflow for model construction.

Related Files

File	Relevance
.matlab\agentic-toolkits\simulink\tools\model_read\model_read.p	SATK tool implementation — model_edit is likely defined here or in a sibling file
.matlab\agentic-toolkits\simulink\VERSION	SATK version: 2026.07.22

Notes (optional)

• create_subsystem and configure operations succeed without layout_mode. The constraint appears specific to add_block (and possibly delete, replace_block, disconnect).
• The tool schema declares layout_mode as optional ("required": ["model", "targets", "params", "compile"] for model_query_params; for model_edit the required fields are ["model", "scope", "operations"]). The conditional requirement is not reflected in the schema or in any validation message.
• The #ref scoping error when layout_mode is provided may be a distinct bug: ref is documented as scoped to a single model_edit call, but the error message references #StabilityControlSystem which is the model name in the parent string, not a ref — suggesting the error message may be conflating the parent path syntax with the #ref syntax.
• This may be a server-side validation issue in the SATK tool implementation rather than an agent-side problem.

Additional Context

Reproduced by attempting D02 — Spec-Driven Plant Model Creation for Closed-Loop Simulation slAgenticTaskExplorer exercise.

[derrick-mw]

Hey @troyp76 ,

This issue was addressed in the latest SATK release. https://github.com/matlab/simulink-agentic-toolkit/releases/tag/2026.07.29

Please let us know if you still encounter this issue after installing the latest version.

Thanks,
Derrick

[troyp76]

Hi Derrick,

Seems to be working now after installing the new release.

Thanks,
Troy