fix(vlm): _clean_json returns first complete JSON object, not brace span

find('{')..rfind('}') spans two emitted objects (e.g. an example then the
answer) and fails the caller's json.loads. Use JSONDecoder().raw_decode to
take the first complete object; fall back to the brace span on decode error.

Takes effect live only after a Space redeploy (scripts/sync_spaces.ps1).
Not CI-unit-testable: the module eager-loads the model at import.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app.py

@@ -25,6 +25,7 @@ clean JSON.
 
 from __future__ import annotations
 
+import json
 import re
 
 import cv2
@@ -104,9 +105,18 @@ def _clean_json(text: str) -> str:
     fence = re.search(r"```(?:json)?\s*(.*?)```", text, flags=re.DOTALL)
     if fence:
         text = fence.group(1)
-    start, end = text.find("{"), text.rfind("}")
-    if start != -1 and end > start:
-        text = text[start : end + 1]
+    # Return the FIRST complete JSON object. A plain find('{')..rfind('}') span
+    # breaks when the model emits two objects (e.g. an example then the answer):
+    # the slice would span the gap between them and fail the caller's json.loads.
+    start = text.find("{")
+    if start != -1:
+        try:
+            obj, _ = json.JSONDecoder().raw_decode(text[start:])
+            return json.dumps(obj)
+        except json.JSONDecodeError:
+            end = text.rfind("}")  # fallback: original brace-span heuristic
+            if end > start:
+                return text[start : end + 1].strip()
     return text.strip()