Document prompt cache control behavior

docs/internal/adapters.md

@@ -22,11 +22,13 @@ CLI adapter:
 
 - Input: process args, filesystem config/assets, environment.
 - Output: exit code, stdout artifact/prepared output, stderr summaries/errors.
+- `run` summaries include cache usage counters only when either parsed cache counter is non-zero.
 
 HTTP adapter:
 
 - Input: JSON request body (`runRequestDTO`).
 - Output: JSON success/error body with mapped status codes.
+- Success metadata includes token usage plus cache usage counters.
 
 Filesystem repositories:
 
@@ -93,6 +95,9 @@ Artifact refs:
 LLM adapter:
 
 - endpoint appends `/chat/completions`.
+- rendered messages without cache control serialize with string `content`.
+- rendered messages with cache control serialize as one text content block with `cache_control`.
+- compatible cache usage response fields are parsed into domain token usage.
 - non-2xx responses map to request failure errors.
 - malformed responses (including missing/empty first choice content) are errors.
 
@@ -142,3 +147,4 @@ Behavior highlights:
 - External request/response strictness is part of contract stability.
 - Prepared-render output never includes resolved API key values.
 - Outbound OpenAI-compatible request includes only currently serialized fields (`model`, `messages`, optional `temperature`, `max_tokens`, `top_p`, optional `service_tier`, optional `response_format`).
+- Outbound cache control is message-level only; no top-level cache-control/session fields are serialized.