feat: reveal all hidden shapes with Shift+H, release SAM3 VRAM on idle and on demand (REQ-191, REQ-192)

backend/api/sam3.py

@@ -0,0 +1,25 @@
+"""SAM3 engine control routes (REQ-192)."""
+
+from fastapi import APIRouter, HTTPException
+
+from backend import jobs
+
+router = APIRouter(prefix="/api/sam3", tags=["sam3"])
+
+
+@router.post("/release")
+def release() -> dict:
+    """Free the SAM3 model's VRAM now — never while the card is busy.
+
+    The same non-blocking `gpu_lock` rule as an interactive assist (REQ-065):
+    a job or assist in flight wins, and the caller is told to try again.
+    """
+    if not jobs.gpu_lock.acquire(blocking=False):
+        raise HTTPException(409, "GPU busy — assist or job in flight, try again in a moment")
+    try:
+        from backend import sam3_engine
+
+        released = sam3_engine.release_engine()
+        return {"released": released, "model_loaded": sam3_engine.engine_is_loaded()}
+    finally:
+        jobs.gpu_lock.release()