diff --git a/frontend/src/capture/SessionCapture.svelte b/frontend/src/capture/SessionCapture.svelte
index c68ad85..8e200b4 100644
--- a/frontend/src/capture/SessionCapture.svelte
+++ b/frontend/src/capture/SessionCapture.svelte
@@ -70,10 +70,12 @@
 
   let fileInput: HTMLInputElement;
 
-  // Auto-run the mask when entering the mask screen and whenever the sheet or
-  // sensitivity changes, so the overlay (and preview) is populated without the
-  // owner having to press Approve first.
-  $: if (kind === 'mask' && cap.source && cap.source.widthPx > 0) {
+  // Auto-run the mask so the overlay (and preview) populate without the owner
+  // pressing Approve first. `controlKey` changes only on sheet/sensitivity
+  // edits (never on the overlay itself), so this fires on entry and on each
+  // control change - but not when approveMask settles the overlay (no loop).
+  $: controlKey = kind === 'mask' && cap.control ? `${cap.control.sheet}:${cap.control.sensitivity}` : null;
+  $: if (controlKey && cap.source && cap.source.widthPx > 0) {
     void session.approveMask();
   }