DiffusionGemma: set UNSLOTH_IS_PRESENT for the shim subprocess

A clean install could not run DiffusionGemma: the runner spawns
python -m unsloth_zoo.diffusion_studio.shim, and unsloth_zoo refuses to
import unless UNSLOTH_IS_PRESENT is set (normally by import unsloth). The
shim never imports unsloth, so the subprocess died with
'Please install Unsloth via pip install unsloth!' and the model load
failed with a 500. Set the flag in the runner child env, as unsloth does
on import.

studio/backend/core/inference/llama_cpp.py

@@ -1042,6 +1042,10 @@ class LlamaCppBackend:
 
     @property
     def supports_tools(self) -> bool:
+        # DiffusionGemma serves via the visual runner, whose live per-step canvas
+        # frames are dropped by the agentic tool loop; never route it through tools.
+        if self._is_diffusion:
+            return False
         return self._supports_tools
 
     @property
@@ -2523,6 +2527,10 @@ class LlamaCppBackend:
         ]
 
         env = child_env_without_native_path_secret()
+        # `python -m unsloth_zoo.diffusion_studio.shim` imports unsloth_zoo, which
+        # refuses to load unless UNSLOTH_IS_PRESENT is set (normally by `import
+        # unsloth`). The shim never imports unsloth, so set it here as unsloth does.
+        env["UNSLOTH_IS_PRESENT"] = "1"
         env["DG_VISUAL_BIN"] = visual_bin
         env["DG_GPU"] = gpu
         # The file-override shim imports its sibling visual_engine; put its dir on PYTHONPATH.

studio/frontend/src/components/assistant-ui/markdown-text.tsx

@@ -285,11 +285,14 @@ function CodeBlockActions({
 }
 
 // DiffusionGemma renders its denoising live in the bubble (see DiffusionCanvas in
-// thread.tsx), so it no longer forces HTML into an iframe artifact; it follows the
-// same artifact rules as every other model.
+// thread.tsx) and has the artifacts canvas on by default, so a full-HTML answer
+// (e.g. a playable game) renders as an interactive card without the global toggle.
 function StreamdownBlock(props: BlockProps) {
   const shouldCollapseHtmlArtifacts = useChatRuntimeStore(
-    (state) => state.artifactsEnabled || state.collapseHtmlArtifacts,
+    (state) =>
+      state.artifactsEnabled ||
+      state.collapseHtmlArtifacts ||
+      state.loadedIsDiffusion,
   );
   const messageHasRenderableRenderHtmlTool = useAuiState(({ message }) =>
     message.parts.some(isRenderableRenderHtmlToolPart),