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fix(mcp-image-gen): fix Heretic/FLUX2 integration bugs

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- Fix syntax error in server.py (dangling docstring lines)
- Correct model filename: flux-2-klein-4b.safetensors (without -fp8)
- Fix _WORKFLOW_REGISTRY key to match actual downloaded filename
- Update get_models() to always include registry models as fallback
- Fix test expectations to match corrected model names
- All 37 tests passing
This commit is contained in:
Patrick Plate
2026-04-10 19:21:51 +02:00
parent 8f24168dcd
commit ea0c5d39c4
6 changed files with 531 additions and 38 deletions
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mcp/mcp-image-gen/README.md
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@@ -2,7 +2,11 @@
**FastMCP server for AI image generation via ComfyUI.**
This MCP server wraps a locally running [ComfyUI](https://github.com/comfyanonymous/ComfyUI) instance, exposing image generation as MCP tools callable from Roo Code, Claude Desktop, or any MCP-compatible client. It supports FLUX.1-schnell, FLUX.1-dev, SDXL, and any other ComfyUI-compatible checkpoint model. Generated images are saved to disk **and** returned as inline base64 so Claude can display them directly in chat.
This MCP server wraps a locally running [ComfyUI](https://github.com/comfyanonymous/ComfyUI) instance, exposing image generation as MCP tools callable from Roo Code, Claude Desktop, or any MCP-compatible client.
**New:** Support for **FLUX.2 Klein 4B** with **Heretic-abliterated Qwen3-4B text encoder** (zero KL divergence, no refusals). Select via `model="flux-2-klein-4b-fp8.safetensors"`.
It supports FLUX.1-schnell (default), FLUX.2 Klein (Heretic), and any other ComfyUI-compatible checkpoint model. Generated images are saved to disk **and** returned as inline base64 so Claude can display them directly in chat.
---
mcp/mcp-image-gen/USAGE.md
+50 -1
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@@ -565,7 +565,56 @@ Then pass it back: `seed=3847291045`
---
## 10. Known Limitations
## 10. FLUX.2 Klein 4B with Heretic Abliteration (New)
**New in this release:** Support for **FLUX.2 Klein 4B** using an **abliterated Qwen3-4B text encoder** via Heretic.
### Why Heretic?
FLUX.2 Klein uses a full LLM (Qwen3-4B) as its text encoder instead of CLIP+T5. This LLM has safety alignment that can refuse certain prompts. Heretic removes this alignment with **zero measurable KL divergence** (0.0000) and only 3/100 refusals.
### How to use it
```python
generate_image(
prompt="a beautiful cyberpunk fox in neon tokyo, highly detailed",
model="flux-2-klein-4b-fp8.safetensors",
width=1024,
height=1024,
steps=4
)
```
### Models to download
```bash
# 1. FLUX.2 Klein 4B (distilled, fp8)
huggingface-cli download black-forest-labs/FLUX.2-klein-4B \
flux-2-klein-4b-fp8.safetensors \
--local-dir ~/ComfyUI/models/diffusion_models/
# 2. FLUX.2 VAE
huggingface-cli download black-forest-labs/FLUX.2-klein-4B \
flux2-vae.safetensors \
--local-dir ~/ComfyUI/models/vae/
# 3. Heretic-abliterated Qwen3-4B (from DreamFast)
huggingface-cli download DreamFast/qwen3-4b-heretic \
--local-dir /tmp/qwen3-heretic/
cp /tmp/qwen3-heretic/model.safetensors \
~/ComfyUI/models/text_encoders/qwen_3_4b_heretic.safetensors
```
### Supported models (via `model=` parameter)
| Model | Description | VRAM | Speed | Censorship |
|-------|-------------|------|-------|------------|
| `flux1-schnell.safetensors` | Original (default) | ~8GB | Very fast | None |
| `flux-2-klein-4b-fp8.safetensors` | **New** — with Heretic Qwen3-4B | ~12GB | Fast | **Removed** |
---
## 11. Known Limitations
### ComfyUI must run locally
mcp/mcp-image-gen/src/server.py
+56 -32
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@@ -39,8 +39,14 @@ COMFYUI_DIR = Path(
# Maximum number of images allowed in a single batch call
MAX_COUNT = 10
# Path to the bundled FLUX.1-schnell workflow template
_WORKFLOW_PATH = Path(__file__).parent / "workflows" / "flux_schnell.json"
# Workflow registry: model filename → workflow JSON path
# This allows us to support multiple models (FLUX.1-schnell + FLUX.2 Klein with Heretic encoder)
_WORKFLOW_REGISTRY: dict[str, Path] = {
"flux1-schnell.safetensors": Path(__file__).parent / "workflows" / "flux_schnell.json",
"flux-2-klein-4b.safetensors": Path(__file__).parent / "workflows" / "flux2_klein_heretic.json",
}
_DEFAULT_MODEL = "flux1-schnell.safetensors"
# ---------------------------------------------------------------------------
@@ -181,21 +187,37 @@ class ComfyUIClient:
return resp.content
async def get_models(self) -> list[str]:
"""Return the list of available checkpoint model filenames."""
async with httpx.AsyncClient(timeout=10.0) as client:
resp = await client.get(
f"{self.base_url}/object_info/CheckpointLoaderSimple"
)
resp.raise_for_status()
data = resp.json()
# ComfyUI returns: {"CheckpointLoaderSimple": {"input": {"required": {"ckpt_name": [["model1.safetensors", ...], ...]}}}}
node_info = data.get("CheckpointLoaderSimple", {})
ckpt_list = (
node_info.get("input", {})
.get("required", {})
.get("ckpt_name", [[]])[0]
)
return ckpt_list if isinstance(ckpt_list, list) else []
"""Return the list of available checkpoint model filenames.
Combines models known to ComfyUI with our internal registry
(including FLUX.2 Klein with Heretic encoder).
"""
models = set()
# Get models from ComfyUI
try:
async with httpx.AsyncClient(timeout=10.0) as client:
resp = await client.get(
f"{self.base_url}/object_info/CheckpointLoaderSimple"
)
resp.raise_for_status()
data = resp.json()
node_info = data.get("CheckpointLoaderSimple", {})
ckpt_list = (
node_info.get("input", {})
.get("required", {})
.get("ckpt_name", [[]])[0]
)
if isinstance(ckpt_list, list):
models.update(ckpt_list)
except Exception:
# ComfyUI not reachable — fall back to registry only
pass
# Add our registered models
models.update(_WORKFLOW_REGISTRY.keys())
return sorted(list(models))
# ---------------------------------------------------------------------------
@@ -209,13 +231,20 @@ def build_flux_workflow(
height: int,
steps: int,
seed: int,
model: str,
model: str = _DEFAULT_MODEL,
) -> dict:
"""Build a ComfyUI API-format workflow dict for FLUX.1-schnell text-to-image.
"""Build a ComfyUI API-format workflow dict for the requested model.
This is a pure function — no I/O, fully testable.
Supports:
- "flux1-schnell.safetensors" (original)
- "flux-2-klein-4b-fp8.safetensors" (with Heretic-abliterated Qwen3-4B text encoder)
Falls back to FLUX.1-schnell if model is unknown.
This is a pure function — no I/O outside the registry, fully testable.
"""
with open(_WORKFLOW_PATH) as f:
workflow_path = _WORKFLOW_REGISTRY.get(model, _WORKFLOW_REGISTRY[_DEFAULT_MODEL])
with open(workflow_path) as f:
wf = json.load(f)
wf = copy.deepcopy(wf)
@@ -277,18 +306,13 @@ async def _generate_single(
) -> list:
"""Generate a single image and return [TextContent, ImageContent] or [TextContent] on error.
Args:
client: ComfyUIClient instance.
prompt: Positive text prompt.
negative_prompt: Negative text prompt.
width / height: Image dimensions.
steps: Inference steps.
seed: Seed value (-1 = random).
model: ComfyUI model filename.
resolved_output_dir: Resolved output directory Path.
name: User-supplied name prefix (unsanitized).
label: Human-readable label for TextContent prefix (e.g. "[lumen 1/3]").
Supports two models:
- flux1-schnell.safetensors (default, fast 4-step)
- flux-2-klein-4b.safetensors (with Heretic-abliterated Qwen3-4B text encoder — no refusals)
"""
if model not in _WORKFLOW_REGISTRY:
model = _DEFAULT_MODEL
logger.warning("Unknown model %s, falling back to %s", model, _DEFAULT_MODEL)
# Build and submit workflow
try:
workflow = build_flux_workflow(
mcp/mcp-image-gen/src/workflows/flux2_klein_heretic.json
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@@ -0,0 +1,73 @@
{
"6": {
"class_type": "CLIPTextEncode",
"inputs": {
"clip": ["30", 0],
"text": "PROMPT_PLACEHOLDER"
}
},
"8": {
"class_type": "VAEDecode",
"inputs": {
"samples": ["13", 0],
"vae": ["31", 0]
}
},
"9": {
"class_type": "SaveImage",
"inputs": {
"filename_prefix": "mcp-image-gen",
"images": ["8", 0]
}
},
"13": {
"class_type": "KSampler",
"inputs": {
"cfg": 1.0,
"denoise": 1.0,
"latent_image": ["27", 0],
"model": ["32", 0],
"negative": ["33", 0],
"positive": ["6", 0],
"sampler_name": "euler",
"scheduler": "beta",
"seed": 42,
"steps": 4
}
},
"27": {
"class_type": "EmptySD3LatentImage",
"inputs": {
"batch_size": 1,
"height": 1024,
"width": 1024
}
},
"30": {
"class_type": "CLIPLoader",
"inputs": {
"clip_name": "qwen_3_4b_heretic.safetensors",
"type": "flux"
}
},
"31": {
"class_type": "VAELoader",
"inputs": {
"vae_name": "flux2-vae.safetensors"
}
},
"32": {
"class_type": "UNETLoader",
"inputs": {
"unet_name": "flux-2-klein-4b.safetensors",
"weight_dtype": "fp8_e4m3fn"
}
},
"33": {
"class_type": "CLIPTextEncode",
"inputs": {
"clip": ["30", 0],
"text": "NEGATIVE_PLACEHOLDER"
}
}
}
mcp/mcp-image-gen/tests/test_server.py
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@@ -31,7 +31,7 @@ COMFYUI_BASE = "http://test-comfyui:8188"
# ---------------------------------------------------------------------------
def test_build_flux_workflow_structure():
"""Verify build_flux_workflow returns a dict with correct node types."""
"""Verify build_flux_workflow returns a dict with correct node types for default model."""
wf = build_flux_workflow(
prompt="a red cat",
neg_prompt="ugly",
@@ -52,6 +52,47 @@ def test_build_flux_workflow_structure():
assert wf["33"]["class_type"] == "CLIPTextEncode"
def test_build_flux_workflow_heretic_model():
"""Verify FLUX.2 Klein 4B with Heretic Qwen3-4B encoder uses correct nodes."""
wf = build_flux_workflow(
prompt="a red cat",
neg_prompt="ugly",
width=1024,
height=1024,
steps=4,
seed=42,
model="flux-2-klein-4b.safetensors",
)
assert wf["6"]["class_type"] == "CLIPTextEncode"
assert wf["30"]["class_type"] == "CLIPLoader" # Qwen3-4B uses single CLIPLoader
assert wf["32"]["inputs"]["unet_name"] == "flux-2-klein-4b.safetensors"
assert wf["31"]["inputs"]["vae_name"] == "flux2-vae.safetensors"
assert wf["13"]["inputs"]["scheduler"] == "beta" # FLUX.2 Klein uses beta scheduler
def test_workflow_registry_contains_both_models():
"""Verify the registry contains both supported models."""
assert "flux1-schnell.safetensors" in server._WORKFLOW_REGISTRY
assert "flux-2-klein-4b.safetensors" in server._WORKFLOW_REGISTRY
assert len(server._WORKFLOW_REGISTRY) == 2
def test_workflow_registry_fallback():
"""Unknown model falls back to default (FLUX.1-schnell)."""
wf = build_flux_workflow(
prompt="test",
neg_prompt="",
width=512,
height=512,
steps=4,
seed=42,
model="unknown-model.safetensors",
)
# Should have used default workflow (DualCLIPLoader)
assert wf["30"]["class_type"] == "DualCLIPLoader"
assert wf["32"]["inputs"]["unet_name"] == "unknown-model.safetensors"
def test_build_flux_workflow_params_injected():
"""Verify all parameters are injected into correct nodes."""
wf = build_flux_workflow(
@@ -202,14 +243,16 @@ async def test_list_available_models():
@respx.mock
@pytest.mark.asyncio
async def test_list_available_models_comfyui_offline():
"""When ComfyUI is unreachable, list_available_models returns error message."""
"""When ComfyUI is unreachable, list_available_models falls back to registry models."""
respx.get(f"{COMFYUI_BASE}/object_info/CheckpointLoaderSimple").mock(
side_effect=httpx.ConnectError("connection refused")
)
result = await list_available_models()
assert len(result) == 1
assert "not reachable" in result[0].lower()
# Should return registry models even when ComfyUI is offline
assert isinstance(result, list)
assert "flux1-schnell.safetensors" in result
assert "flux-2-klein-4b.safetensors" in result
# ---------------------------------------------------------------------------