fix(voice): detach nested contacts snapshots

deep-clone retained aircraft items, provenance and subject data

add a regression for nested mutation across repeated snapshot reads

src/data/militaryAwareness.test.mjs

@@ -2608,17 +2608,18 @@ test('the voice query snapshot is a detached copy of the rendered aircraft cohor
     assert.equal(first.cohorts.flights.provenance.enabled, true);
     assert.equal(first.cohorts.flights.items[0].icao24, 'nearby');
     first.cohorts.flights.items[0].icao24 = 'mutated';
+    first.cohorts.flights.items[0].position.x = 99;
     first.cohorts.flights.provenance.source = 'mutated';
-    assert.equal(
-      militaryAwarenessLayer.getAircraftQuerySnapshot().cohorts.flights.items[0]
-        .icao24,
-      'nearby',
-    );
-    assert.notEqual(
-      militaryAwarenessLayer.getAircraftQuerySnapshot().cohorts.flights
-        .provenance.source,
-      'mutated',
-    );
+    first.cohorts.flights.provenance.stats.coverage = { radiusM: 1 };
+    first.subject.position.x = 77;
+    const second = militaryAwarenessLayer.getAircraftQuerySnapshot();
+    assert.equal(second.cohorts.flights.items[0].icao24, 'nearby');
+    assert.equal(second.cohorts.flights.items[0].position.x, nearbyPosition.x);
+    assert.notEqual(second.cohorts.flights.provenance.source, 'mutated');
+    assert.notDeepEqual(second.cohorts.flights.provenance.stats.coverage, {
+      radiusM: 1,
+    });
+    assert.equal(second.subject.position.x, subjectPosition.x);
   } finally {
     runtime.restore();
     restoreCollections();

src/layers/awareness/controls.js

@@ -105,23 +105,19 @@ export function createControls({ state: layerState, services, parts, source }) {
           truncated:
             !Number.isFinite(cohort.summary?.count) ||
             cohort.summary?.truncated === true,
-          items: (cohort.summary?.navigationNearest || []).map((item) => ({
-            ...item,
-          })),
+          // These records carry structured values such as Cartesian positions.
+          // A shallow spread would let a voice consumer mutate the retained
+          // Contacts cohort through the advertised read-only snapshot.
+          items: structuredClone(cohort.summary?.navigationNearest || []),
           source: cohort.source || null,
           provenance: cohort.provenance
-            ? {
-                ...cohort.provenance,
-                stats: cohort.provenance.stats
-                  ? { ...cohort.provenance.stats }
-                  : undefined,
-              }
+            ? structuredClone(cohort.provenance)
             : null,
           reason: cohort.summary?.reason || null,
         };
       }
       return {
-        subject: { ...layerState.results.subject },
+        subject: structuredClone(layerState.results.subject),
         evaluatedAt: layerState.results.evaluatedAt,
         radiusM: layerState.results.radiusM,
         cohorts,