Add LLM execution summaries

docs/internal/llm.md

@@ -223,6 +223,12 @@ also records that exhaustion and the attempts in that generation. Those fields
 do not include repair generations, and zero attempts means unavailable rather
 than proof that no request was sent.
 
+Every execution that reaches PromptKit returns an optional request-local
+`execution` summary. It contains only terminal aggregate attempts, retry and
+repair counts, durations, outcome and failure classification, status, and
+presence-aware token usage. Preparation failures have no summary; later local
+decode failures retain the upstream terminal summary without changing it.
+
 When PromptKit rejects backend admission before generation, the adapter maps
 `promptkit.ErrCapacityExceeded` to
 `contracts.ErrLLMCapacityExceeded`, retaining prompt context and a redacted