fix(frontend): untrack the splice's own .length read in useMany reconcile

The previous fix wrapped only the comparison reads in `untrack`, but
`handles.splice(0, handles.length, ...next)` still reads `.length`
under the effect's tracking scope — same feedback loop, same
`effect_update_depth_exceeded`.

Move the whole "compare + splice" block inside `untrack`. The
downstream notification on splice still fires (untrack suppresses
dependency subscriptions on the producer side, not write
notifications), so consumers of `handles` still re-render.

frontend/src/lib/userDraft.svelte.ts

@@ -416,14 +416,17 @@ export const UserDraft = {
 			// produce reference-equal arrays. Avoids dirtying downstream
 			// reactive readers on no-op `$effect` re-runs.
 			//
-			// The read side is wrapped in `untrack` so the effect doesn't
-			// register `handles` as one of its own dependencies; otherwise
-			// the splice below would re-fire the effect, splice again, …
-			// (Svelte raises `effect_update_depth_exceeded`).
-			const unchanged = untrack(
-				() => handles.length === next.length && handles.every((h, i) => h === next[i])
-			)
-			if (!unchanged) handles.splice(0, handles.length, ...next)
+			// Both the comparison reads AND the splice's own `.length` read
+			// run under `untrack` so the effect doesn't register `handles`
+			// as one of its own dependencies — otherwise the splice would
+			// re-fire the effect, splice again, … (Svelte raises
+			// `effect_update_depth_exceeded`). The splice's downstream
+			// notification still propagates; `untrack` only suppresses the
+			// dependency subscription on the producer side.
+			untrack(() => {
+				const unchanged = handles.length === next.length && handles.every((h, i) => h === next[i])
+				if (!unchanged) handles.splice(0, handles.length, ...next)
+			})
 		}
 
 		// Synchronous initial reconcile so single-spec callers (`use()`) get a