chore: update OpenAPI spec from monorepo

.speakeasy/in.openapi.yaml

@@ -37,6 +37,7 @@ components:
     ActivityItem:
       example:
         byok_usage_inference: 0.012
+        cached_tokens: 10
         completion_tokens: 125
         date: '2025-08-24'
         endpoint_id: '550e8400-e29b-41d4-a716-446655440000'
@@ -53,6 +54,10 @@ components:
           example: 0.012
           format: 'double'
           type: 'number'
+        cached_tokens:
+          description: 'Total prompt tokens read from the provider prompt cache (cache hits). Generally a subset of `prompt_tokens`; for replayed response-cache hits the provider may report the two counters over disjoint token sets, so `cached_tokens` can exceed `prompt_tokens`.'
+          example: 10
+          type: 'integer'
         completion_tokens:
           description: 'Total completion tokens generated'
           example: 125
@@ -110,11 +115,13 @@ components:
         - 'prompt_tokens'
         - 'completion_tokens'
         - 'reasoning_tokens'
+        - 'cached_tokens'
       type: 'object'
     ActivityResponse:
       example:
         data:
           - byok_usage_inference: 0.012
+            cached_tokens: 10
             completion_tokens: 125
             date: '2025-08-24'
             endpoint_id: '550e8400-e29b-41d4-a716-446655440000'
@@ -33032,6 +33039,7 @@ paths:
               example:
                 data:
                   - byok_usage_inference: 0.012
+                    cached_tokens: 10
                     completion_tokens: 125
                     date: '2025-08-24'
                     endpoint_id: '550e8400-e29b-41d4-a716-446655440000'