feat: port VLM + FLUX from BTE (Phase 4b)

VLM router (POST /vlm/analyze):
- Proxies to Spark 2 (Qwen3-VL via vLLM, OpenAI-compatible /v1/chat/completions)
- Port of BTE Svrnty.Bte.Domain/Features/AssetContext/OpenAiVlmClient.cs
  + VlmRubric.cs (rubric prompt builder + score parser)
- Anthropic dialect intentionally dropped — sovereign-only
- New rubric_mode="raw" passes brand_context through verbatim so BTE
  ExtractBrandSaga / ImageSetSourceReader (extraction-style prompts that
  expect their own JSON schema) get unwrapped JSON back without losing
  the score-axis path

FLUX router (POST /flux/render):
- Proxies to Spark 1 (FLUX.2-dev on ComfyUI; /prompt + /history poll + /view)
- Port of SparkBComfyClient.cs + LocalFluxImageProvider.cs + StopgapFluxWorkflow.cs
- Accepts a pre-assembled workflow_json (BTE IRecipeAssembler emits one)
  or builds the stopgap FLUX.2 graph from prompt + dims

Tests (pytest):
- test_vlm_parse.py — rubric prompt + score parse, 502 on Spark-down, mocked round-trip
- test_flux_workflow.py — stopgap graph shape, seed variance/determinism, 502 on Spark-down
- test_healthz.py updated (palette/rembg still 4a stubs)

16 pytest tests green.

Smoke (no Spark reachable):
- GET /healthz → 200 {"status":"ok"}
- POST /vlm/analyze → 502 "Spark 2 unreachable" (clear error)
- POST /flux/render → 502 "Spark 1 unreachable" (clear error)

Per BTE refactor audit §3 V — vision capabilities extracted from BTE to the
sovereign vision gateway. Phase 4c (delete-from-BTE) + Phase 4d (HTTP adapter)
follow in BTE.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/svrnty_vision/routers/flux.py

@@ -1,17 +1,247 @@
-"""FLUX image generation — stub until Phase 4b wires the ComfyUI HTTP client."""
+"""FLUX image generation — proxies to Spark 1 (ComfyUI HTTP API).
 
+Ported from BTE's SparkBComfyClient.cs + LocalFluxImageProvider.cs +
+StopgapFluxWorkflow.cs (Phase 4b). Workflow is either supplied by the caller
+(BTE's IRecipeAssembler emits a full graph) or assembled inline from the
+stopgap FLUX.2 template.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import base64
+import json
+import random
+import time
+import urllib.parse
+from typing import Any
+
+import httpx
 from fastapi import APIRouter, HTTPException, status
+from pydantic import BaseModel, Field
+
+from svrnty_vision.settings import settings
 
 router = APIRouter(prefix="/flux", tags=["flux"])
 
 
-@router.post("/render")
-async def render() -> None:
-    """Render an image via Spark 1 (FLUX on ComfyUI).
+# Default values match BTE's StopgapFluxWorkflow.cs.
+DEFAULT_GUIDANCE = 2.5
+DEFAULT_STEPS = 20
+POLL_INTERVAL_SECONDS = 2.0
 
-    Phase 4a: stub. Phase 4b: proxies to Spark 1 ComfyUI workflow.
+
+class RenderRequest(BaseModel):
+    """Either `workflow_json` (a pre-assembled ComfyUI graph) or `prompt` + dims
+    (we build the stopgap FLUX.2-dev graph). `workflow_json` wins when both set.
     """
+
+    prompt: str | None = None
+    width: int = 1024
+    height: int = 1024
+    workflow_json: str | None = None
+    guidance: float = DEFAULT_GUIDANCE
+    steps: int = DEFAULT_STEPS
+    seed: int | None = None  # null → random per call (ComfyUI dedup avoidance)
+
+
+class RenderResponse(BaseModel):
+    prompt_id: str
+    image_base64: str
+    content_type: str = "image/png"
+    duration_ms: int
+    provider: str = "local"
+    model: str = "flux2"
+
+
+def build_stopgap_workflow(
+    prompt: str,
+    width: int,
+    height: int,
+    guidance: float = DEFAULT_GUIDANCE,
+    steps: int = DEFAULT_STEPS,
+    seed: int | None = None,
+) -> str:
+    """Ported from StopgapFluxWorkflow.Build (Svrnty.Bte.Shared.Recipes).
+
+    FLUX.2 stack on Spark 1: flux2_dev_fp8mixed UNET, Mistral-3 CLIP (type "flux2"),
+    flux2-vae. KSampler cfg=1.0; distilled guidance via FluxGuidance node.
+    Random seed per call: ComfyUI dedupes identical workflows.
+    """
+    if seed is None:
+        seed = random.randint(1, 2**31 - 1)
+
+    graph: dict[str, Any] = {
+        "5": {
+            "class_type": "EmptySD3LatentImage",
+            "inputs": {"width": width, "height": height, "batch_size": 1},
+        },
+        "6": {
+            "class_type": "CLIPTextEncode",
+            "inputs": {"clip": ["11", 0], "text": prompt},
+        },
+        "7": {
+            "class_type": "CLIPTextEncode",
+            "inputs": {"clip": ["11", 0], "text": ""},
+        },
+        "8": {
+            "class_type": "VAEDecode",
+            "inputs": {"samples": ["13", 0], "vae": ["10", 0]},
+        },
+        "9": {
+            "class_type": "SaveImage",
+            "inputs": {"filename_prefix": "bte", "images": ["8", 0]},
+        },
+        "10": {
+            "class_type": "VAELoader",
+            "inputs": {"vae_name": "flux2-vae.safetensors"},
+        },
+        "11": {
+            "class_type": "CLIPLoader",
+            "inputs": {
+                "clip_name": "mistral_3_small_flux2_fp8.safetensors",
+                "type": "flux2",
+            },
+        },
+        "12": {
+            "class_type": "UNETLoader",
+            "inputs": {
+                "unet_name": "flux2_dev_fp8mixed.safetensors",
+                "weight_dtype": "default",
+            },
+        },
+        "13": {
+            "class_type": "KSampler",
+            "inputs": {
+                "model": ["12", 0],
+                "positive": ["26", 0],
+                "negative": ["7", 0],
+                "latent_image": ["5", 0],
+                "seed": seed,
+                "steps": steps,
+                "cfg": 1.0,
+                "sampler_name": "euler",
+                "scheduler": "simple",
+                "denoise": 1.0,
+            },
+        },
+        "26": {
+            "class_type": "FluxGuidance",
+            "inputs": {"conditioning": ["6", 0], "guidance": guidance},
+        },
+    }
+    return json.dumps(graph)
+
+
+async def _queue_prompt(
+    client: httpx.AsyncClient, endpoint: str, workflow_json: str
+) -> str:
+    workflow = json.loads(workflow_json)
+    resp = await client.post(f"{endpoint}/prompt", json={"prompt": workflow})
+    resp.raise_for_status()
+    body = resp.json()
+    if "prompt_id" not in body:
+        raise HTTPException(
+            status_code=status.HTTP_502_BAD_GATEWAY,
+            detail=f"ComfyUI /prompt returned no prompt_id: {body}",
+        )
+    return body["prompt_id"]
+
+
+async def _poll_history(
+    client: httpx.AsyncClient, endpoint: str, prompt_id: str
+) -> list[dict[str, str]]:
+    deadline = time.monotonic() + settings.vision_request_timeout_seconds
+    while time.monotonic() < deadline:
+        resp = await client.get(f"{endpoint}/history/{prompt_id}")
+        resp.raise_for_status()
+        doc = resp.json()
+        entry = doc.get(prompt_id)
+        if entry and entry.get("status", {}).get("completed"):
+            return _extract_images(entry)
+        await asyncio.sleep(POLL_INTERVAL_SECONDS)
     raise HTTPException(
-        status_code=status.HTTP_501_NOT_IMPLEMENTED,
-        detail="flux.render not implemented in Phase 4a — see BTE-REFACTOR-EXECUTION-PLAN Phase 4b",
+        status_code=status.HTTP_504_GATEWAY_TIMEOUT,
+        detail=(
+            f"ComfyUI prompt {prompt_id} did not complete within "
+            f"{settings.vision_request_timeout_seconds}s."
+        ),
+    )
+
+
+def _extract_images(entry: dict[str, Any]) -> list[dict[str, str]]:
+    refs: list[dict[str, str]] = []
+    outputs = entry.get("outputs", {})
+    for node in outputs.values():
+        for img in node.get("images", []) or []:
+            refs.append(
+                {
+                    "filename": img.get("filename", ""),
+                    "subfolder": img.get("subfolder", ""),
+                    "type": img.get("type", "output"),
+                }
+            )
+    return refs
+
+
+async def _download_image(
+    client: httpx.AsyncClient, endpoint: str, ref: dict[str, str]
+) -> bytes:
+    qs = urllib.parse.urlencode(
+        {
+            "filename": ref["filename"],
+            "subfolder": ref["subfolder"],
+            "type": ref["type"],
+        }
+    )
+    resp = await client.get(f"{endpoint}/view?{qs}")
+    resp.raise_for_status()
+    return resp.content
+
+
+@router.post("/render", response_model=RenderResponse)
+async def render(req: RenderRequest) -> RenderResponse:
+    """Render an image via Spark 1 (FLUX.2-dev on ComfyUI).
+
+    If `workflow_json` is supplied (e.g. from BTE's IRecipeAssembler), it is
+    POSTed verbatim. Otherwise a stopgap FLUX.2 graph is built from `prompt`.
+    """
+    workflow_json = req.workflow_json
+    if not workflow_json:
+        if not req.prompt:
+            raise HTTPException(
+                status_code=status.HTTP_400_BAD_REQUEST,
+                detail="Provide workflow_json or prompt.",
+            )
+        workflow_json = build_stopgap_workflow(
+            req.prompt, req.width, req.height, req.guidance, req.steps, req.seed
+        )
+
+    endpoint = settings.spark1_flux_url.rstrip("/")
+    started = time.monotonic()
+
+    try:
+        async with httpx.AsyncClient(
+            timeout=settings.vision_request_timeout_seconds
+        ) as client:
+            prompt_id = await _queue_prompt(client, endpoint, workflow_json)
+            images = await _poll_history(client, endpoint, prompt_id)
+            if not images:
+                raise HTTPException(
+                    status_code=status.HTTP_502_BAD_GATEWAY,
+                    detail=f"ComfyUI returned no output images for prompt {prompt_id}.",
+                )
+            png_bytes = await _download_image(client, endpoint, images[0])
+    except httpx.HTTPError as e:
+        raise HTTPException(
+            status_code=status.HTTP_502_BAD_GATEWAY,
+            detail=f"Spark 1 (ComfyUI) at {endpoint} unreachable: {type(e).__name__}: {e}",
+        ) from e
+
+    duration_ms = int((time.monotonic() - started) * 1000)
+    return RenderResponse(
+        prompt_id=prompt_id,
+        image_base64=base64.b64encode(png_bytes).decode("ascii"),
+        content_type="image/png",
+        duration_ms=duration_ms,
     )

src/svrnty_vision/routers/vlm.py

@@ -1,17 +1,193 @@
-"""VLM (vision-language model) analysis — stub until Phase 4b moves Qwen3-VL code."""
+"""VLM (vision-language model) analysis — proxies to Spark 2 (Qwen3-VL via vLLM).
 
+Ported from BTE's OpenAiVlmClient.cs + VlmRubric.cs (Phase 4b). Cloud Anthropic
+dialect intentionally dropped — svrnty-vision is sovereign-only.
+"""
+
+from __future__ import annotations
+
+import base64
+import json
+from decimal import Decimal
+from typing import Any
+
+import httpx
 from fastapi import APIRouter, HTTPException, status
+from pydantic import BaseModel, Field
+
+from svrnty_vision.settings import settings
 
 router = APIRouter(prefix="/vlm", tags=["vlm"])
 
 
-@router.post("/analyze")
-async def analyze() -> None:
-    """Analyze an image with a vision-language model.
+class AnalyzeRequest(BaseModel):
+    """At least one of `image_base64` or `image_url` must be supplied.
 
-    Phase 4a: stub. Phase 4b: proxies to Spark 2 (Qwen3-VL via vLLM).
+    `rubric_mode` is `polished` (premium aesthetic) or `ugc` (organic).
+    `brand_context` is the prompt anchor (brand description / extraction directives).
+    Set `rubric_mode = "raw"` to bypass the brand-scoring rubric and pass
+    `brand_context` through verbatim (used by extraction prompts, e.g. screenshot DNA).
     """
-    raise HTTPException(
-        status_code=status.HTTP_501_NOT_IMPLEMENTED,
-        detail="vlm.analyze not implemented in Phase 4a — see BTE-REFACTOR-EXECUTION-PLAN Phase 4b",
+
+    image_base64: str | None = None
+    image_url: str | None = None
+    content_type: str = "image/png"
+    brand_context: str = ""
+    rubric_mode: str = "polished"
+    model: str | None = None  # override settings.spark2_vlm_model
+    max_tokens: int = 1024
+
+
+class AnalyzeResponse(BaseModel):
+    brand_fit_score: Decimal | None = Field(
+        default=None,
+        description="0.00–5.00, or null when rubric_mode='raw' (no scores parsed)",
     )
+    visual_polish_score: Decimal | None = None
+    rubric_mode: str
+    justification: str = ""
+    model_id: str
+    raw_scores_json: str = Field(
+        description="The JSON object the VLM returned (or its full text if rubric_mode='raw')."
+    )
+
+
+def build_rubric_prompt(brand_context: str, rubric_mode: str) -> str:
+    """Ported from VlmRubric.BuildRubricPrompt.
+
+    `rubric_mode='raw'` bypasses the brand-scoring rubric — caller's brand_context
+    becomes the full prompt (used for extraction-style calls).
+    """
+    if rubric_mode == "raw":
+        return brand_context
+
+    return (
+        "You are a brand-asset reviewer. Brand context:\n"
+        "---\n"
+        f"{brand_context}\n"
+        "---\n"
+        f"Rubric mode: {rubric_mode} (polished = premium production aesthetic; "
+        "ugc = organic, casual, hand-shot feel).\n\n"
+        "Score the attached image on TWO axes, each 0.00 – 5.00:\n"
+        "- brand_fit: how well it embodies the brand voice/tokens above.\n"
+        "- visual_polish: technical execution under the chosen rubric mode.\n\n"
+        "Respond with ONE compact JSON object only — no prose, no fences:\n"
+        '{"brand_fit": <num>, "visual_polish": <num>, "justification": "<≤200 chars>"}'
+    )
+
+
+def parse_scores(
+    response_text: str, rubric_mode: str, model_id: str
+) -> AnalyzeResponse:
+    """Ported from VlmRubric.ParseScores.
+
+    For `rubric_mode='raw'` we return the response text untouched; scores stay None.
+    Callers (e.g. BTE ImageSetSourceReader / ExtractBrandSaga) parse the JSON
+    themselves.
+    """
+    if rubric_mode == "raw":
+        return AnalyzeResponse(
+            brand_fit_score=None,
+            visual_polish_score=None,
+            rubric_mode=rubric_mode,
+            justification="",
+            model_id=model_id,
+            raw_scores_json=response_text,
+        )
+
+    trimmed = response_text.strip()
+    start = trimmed.find("{")
+    end = trimmed.rfind("}")
+    if start < 0 or end <= start:
+        raise HTTPException(
+            status_code=status.HTTP_502_BAD_GATEWAY,
+            detail=f"VLM response did not contain a JSON object: {response_text}",
+        )
+
+    raw_json = trimmed[start : end + 1]
+    try:
+        obj = json.loads(raw_json)
+    except json.JSONDecodeError as e:
+        raise HTTPException(
+            status_code=status.HTTP_502_BAD_GATEWAY,
+            detail=f"VLM JSON parse failed: {e}",
+        ) from e
+
+    return AnalyzeResponse(
+        brand_fit_score=Decimal(str(obj["brand_fit"])),
+        visual_polish_score=Decimal(str(obj["visual_polish"])),
+        rubric_mode=rubric_mode,
+        justification=str(obj.get("justification", "")),
+        model_id=model_id,
+        raw_scores_json=raw_json,
+    )
+
+
+async def _resolve_data_uri(req: AnalyzeRequest) -> str:
+    if req.image_base64:
+        return f"data:{req.content_type};base64,{req.image_base64}"
+    if req.image_url:
+        # vLLM Qwen3-VL accepts http(s) URLs directly; pass through.
+        if req.image_url.startswith(("http://", "https://", "data:")):
+            return req.image_url
+        # Otherwise treat as local path → read + b64.
+        try:
+            with open(req.image_url, "rb") as f:
+                raw = f.read()
+        except OSError as e:
+            raise HTTPException(
+                status_code=status.HTTP_400_BAD_REQUEST,
+                detail=f"image_url unreadable as file: {e}",
+            ) from e
+        return f"data:{req.content_type};base64,{base64.b64encode(raw).decode('ascii')}"
+    raise HTTPException(
+        status_code=status.HTTP_400_BAD_REQUEST,
+        detail="Provide image_base64 or image_url.",
+    )
+
+
+@router.post("/analyze", response_model=AnalyzeResponse)
+async def analyze(req: AnalyzeRequest) -> AnalyzeResponse:
+    """Analyze an image with Qwen3-VL on Spark 2 (vLLM, OpenAI-compatible)."""
+    data_uri = await _resolve_data_uri(req)
+    rubric = build_rubric_prompt(req.brand_context, req.rubric_mode)
+    model = req.model or settings.spark2_vlm_model
+
+    body: dict[str, Any] = {
+        "model": model,
+        "max_tokens": req.max_tokens,
+        "temperature": 0,
+        "messages": [
+            {
+                "role": "user",
+                "content": [
+                    {"type": "text", "text": rubric},
+                    {"type": "image_url", "image_url": {"url": data_uri}},
+                ],
+            }
+        ],
+    }
+
+    url = settings.spark2_vlm_url.rstrip("/") + "/v1/chat/completions"
+    try:
+        async with httpx.AsyncClient(
+            timeout=settings.vision_request_timeout_seconds
+        ) as client:
+            resp = await client.post(url, json=body)
+            resp.raise_for_status()
+            payload = resp.json()
+    except httpx.HTTPError as e:
+        raise HTTPException(
+            status_code=status.HTTP_502_BAD_GATEWAY,
+            detail=f"Spark 2 (vLLM) at {url} unreachable: {type(e).__name__}: {e}",
+        ) from e
+
+    try:
+        text = payload["choices"][0]["message"]["content"] or ""
+    except (KeyError, IndexError, TypeError) as e:
+        raise HTTPException(
+            status_code=status.HTTP_502_BAD_GATEWAY,
+            detail=f"Spark 2 response shape unexpected: {e}",
+        ) from e
+
+    return parse_scores(text, req.rubric_mode, model)

tests/test_flux_workflow.py

@@ -0,0 +1,68 @@
+"""Pytest port of BTE's StopgapFluxWorkflowTests + smoke for /flux/render."""
+
+from __future__ import annotations
+
+import json
+from unittest.mock import patch
+
+import httpx
+from fastapi.testclient import TestClient
+
+from svrnty_vision.routers.flux import build_stopgap_workflow
+from svrnty_vision.server import app
+
+client = TestClient(app)
+
+
+def test_stopgap_workflow_includes_prompt_and_dimensions() -> None:
+    raw = build_stopgap_workflow("a sunlit plate of food", 1024, 1024)
+    assert "a sunlit plate of food" in raw
+    graph = json.loads(raw)
+    assert graph["5"]["inputs"]["width"] == 1024
+    assert graph["5"]["inputs"]["height"] == 1024
+    assert graph["10"]["inputs"]["vae_name"] == "flux2-vae.safetensors"
+    assert graph["11"]["inputs"]["type"] == "flux2"
+    assert graph["12"]["inputs"]["unet_name"] == "flux2_dev_fp8mixed.safetensors"
+
+
+def test_stopgap_workflow_seeds_vary_per_call() -> None:
+    """ComfyUI dedupes identical workflows (execution_cached → empty outputs)."""
+    a = build_stopgap_workflow("x", 512, 512)
+    b = build_stopgap_workflow("x", 512, 512)
+    assert a != b
+
+
+def test_stopgap_workflow_uses_explicit_seed_when_supplied() -> None:
+    a = build_stopgap_workflow("x", 512, 512, seed=42)
+    b = build_stopgap_workflow("x", 512, 512, seed=42)
+    assert a == b
+
+
+def test_render_requires_workflow_or_prompt() -> None:
+    response = client.post("/flux/render", json={"width": 512, "height": 512})
+    assert response.status_code == 400
+
+
+def test_render_returns_502_when_spark1_unreachable() -> None:
+    class _StubClient:
+        def __init__(self, *a, **kw):
+            pass
+
+        async def __aenter__(self):
+            return self
+
+        async def __aexit__(self, *a):
+            return False
+
+        async def post(self, *a, **kw):
+            raise httpx.ConnectError("no comfy")
+
+        async def get(self, *a, **kw):
+            raise httpx.ConnectError("no comfy")
+
+    with patch("svrnty_vision.routers.flux.httpx.AsyncClient", _StubClient):
+        response = client.post(
+            "/flux/render",
+            json={"prompt": "test", "width": 512, "height": 512},
+        )
+    assert response.status_code == 502

tests/test_healthz.py

@@ -15,21 +15,13 @@ def test_healthz_returns_200() -> None:
     assert "version" in body
 
 
-def test_vlm_analyze_returns_501() -> None:
-    response = client.post("/vlm/analyze")
-    assert response.status_code == 501
-
-
-def test_flux_render_returns_501() -> None:
-    response = client.post("/flux/render")
-    assert response.status_code == 501
-
-
 def test_palette_extract_returns_501() -> None:
+    # Still a 4a stub — Phase 4c moved only VLM + FLUX, palette/rembg deferred.
     response = client.post("/palette/extract")
     assert response.status_code == 501
 
 
 def test_rembg_cutout_returns_501() -> None:
+    # Still a 4a stub — Phase 4c moved only VLM + FLUX, palette/rembg deferred.
     response = client.post("/rembg/cutout")
     assert response.status_code == 501

tests/test_vlm_parse.py

@@ -0,0 +1,147 @@
+"""Pytest port of BTE's FakeVlmEvaluationParseTests + VlmRubric parse coverage.
+
+These tests cover the pure-function side of the VLM router (rubric prompt + score
+parsing). The HTTP call to Spark 2 is exercised separately via TestClient with a
+mocked httpx transport.
+"""
+
+from __future__ import annotations
+
+from decimal import Decimal
+from unittest.mock import AsyncMock, patch
+
+import httpx
+import pytest
+from fastapi.testclient import TestClient
+
+from svrnty_vision.routers.vlm import build_rubric_prompt, parse_scores
+from svrnty_vision.server import app
+
+client = TestClient(app)
+
+
+def test_build_rubric_prompt_includes_brand_and_mode() -> None:
+    prompt = build_rubric_prompt("test-brand", "polished")
+    assert "test-brand" in prompt
+    assert "polished" in prompt
+    assert "brand_fit" in prompt
+    assert "visual_polish" in prompt
+
+
+def test_build_rubric_prompt_raw_passes_through_verbatim() -> None:
+    assert build_rubric_prompt("anything goes", "raw") == "anything goes"
+
+
+def test_parse_scores_extracts_canned_payload() -> None:
+    raw = '{"brand_fit":4.20,"visual_polish":3.80,"justification":"clean lighting"}'
+    result = parse_scores(raw, "polished", "qwen-test")
+    assert result.brand_fit_score == Decimal("4.20")
+    assert result.visual_polish_score == Decimal("3.80")
+    assert result.rubric_mode == "polished"
+    assert result.model_id == "qwen-test"
+    assert "brand_fit" in result.raw_scores_json
+
+
+def test_parse_scores_tolerates_leading_or_trailing_prose() -> None:
+    raw = 'sure: {"brand_fit":2,"visual_polish":3}. done.'
+    result = parse_scores(raw, "ugc", "m")
+    assert result.brand_fit_score == Decimal("2")
+    assert result.visual_polish_score == Decimal("3")
+
+
+def test_parse_scores_raw_mode_returns_text_untouched() -> None:
+    raw = '{"subject":"plate","mood":"warm"}'
+    result = parse_scores(raw, "raw", "m")
+    assert result.brand_fit_score is None
+    assert result.visual_polish_score is None
+    assert result.raw_scores_json == raw
+
+
+def test_analyze_requires_image_input() -> None:
+    response = client.post(
+        "/vlm/analyze",
+        json={"brand_context": "x", "rubric_mode": "polished"},
+    )
+    assert response.status_code == 400
+
+
+def test_analyze_returns_502_when_spark2_unreachable() -> None:
+    """Smoke: with no Spark 2 (or a failing transport), gateway surfaces 502.
+
+    Uses a mock async client that raises ConnectError on POST.
+    """
+
+    class _StubClient:
+        def __init__(self, *a, **kw):
+            pass
+
+        async def __aenter__(self):
+            return self
+
+        async def __aexit__(self, *a):
+            return False
+
+        async def post(self, *a, **kw):
+            raise httpx.ConnectError("boom")
+
+    with patch("svrnty_vision.routers.vlm.httpx.AsyncClient", _StubClient):
+        response = client.post(
+            "/vlm/analyze",
+            json={
+                "image_base64": "ZmFrZQ==",
+                "brand_context": "test",
+                "rubric_mode": "polished",
+            },
+        )
+    assert response.status_code == 502
+
+
+def test_analyze_round_trip_with_mocked_spark2() -> None:
+    """Happy path: mock vLLM returns a well-formed score JSON; gateway parses it."""
+
+    canned_response = {
+        "choices": [
+            {
+                "message": {
+                    "content": '{"brand_fit": 4.5, "visual_polish": 4.0, "justification": "ok"}'
+                }
+            }
+        ]
+    }
+
+    class _StubResponse:
+        status_code = 200
+
+        def raise_for_status(self):
+            return None
+
+        def json(self):
+            return canned_response
+
+    class _StubClient:
+        def __init__(self, *a, **kw):
+            pass
+
+        async def __aenter__(self):
+            return self
+
+        async def __aexit__(self, *a):
+            return False
+
+        async def post(self, *a, **kw):
+            return _StubResponse()
+
+    with patch("svrnty_vision.routers.vlm.httpx.AsyncClient", _StubClient):
+        response = client.post(
+            "/vlm/analyze",
+            json={
+                "image_base64": "ZmFrZQ==",
+                "brand_context": "test-brand",
+                "rubric_mode": "polished",
+            },
+        )
+    assert response.status_code == 200, response.text
+    body = response.json()
+    assert Decimal(body["brand_fit_score"]) == Decimal("4.5")
+    assert Decimal(body["visual_polish_score"]) == Decimal("4.0")
+    assert body["rubric_mode"] == "polished"