fix(lease): restore uniform settings array replacement

AMD1213-B1: preserve the gated Claude hook composition explicitly in the lease overlay while restoring last-layer-wins arrays and null tombstones.

packages/mosaic/src/commands/fleet-launch-command.ts

@@ -253,12 +253,9 @@ function cloneValue(value: unknown): unknown {
   return value;
 }
 
-type MergeContext = 'root' | 'hooks' | 'nested';
-
 function mergeObject(
   lower: Record<string, unknown>,
   higher: Record<string, unknown>,
-  context: MergeContext = 'nested',
 ): Record<string, unknown> {
   const result = cloneValue(lower) as Record<string, unknown>;
   for (const [key, highValue] of Object.entries(higher)) {
@@ -267,36 +264,23 @@ function mergeObject(
       continue;
     }
     const lowValue = result[key];
-    if (context === 'hooks' && Array.isArray(lowValue) && Array.isArray(highValue)) {
-      result[key] = [...(lowValue as unknown[]), ...(cloneValue(highValue) as unknown[])];
-      continue;
-    }
     result[key] =
       isPlainObject(lowValue) && isPlainObject(highValue)
-        ? mergeObject(
-            lowValue,
-            highValue,
-            context === 'root' && key === 'hooks' ? 'hooks' : 'nested',
-          )
+        ? mergeObject(lowValue, highValue)
         : cloneValue(highValue);
   }
   return result;
 }
 
 /**
- * Deep object merge. Scalars and arrays replace; null in a higher layer
- * deletes. Exception: hook event arrays directly under the top-level `hooks`
- * key concatenate (base entries first), so an overlay ADDS gating without
- * erasing the base QA hooks that share an event — replacing them would make
- * the gap-7 base/overlay split unimplementable without duplicating base
- * hooks inside the lease overlay. Removing an event entirely still works via
- * the null tombstone.
+ * Deep object merge. Objects merge recursively; scalar and array conflicts
+ * resolve last-layer-wins; null in a higher layer deletes the key.
  */
 export function deepMergeSettings(
   ...layers: ReadonlyArray<Record<string, unknown> | undefined>
 ): Record<string, unknown> {
   return layers.reduce<Record<string, unknown>>(
-    (merged, layer) => (layer === undefined ? merged : mergeObject(merged, layer, 'root')),
+    (merged, layer) => (layer === undefined ? merged : mergeObject(merged, layer)),
     {},
   );
 }