diff --git a/CLAUDE.md b/CLAUDE.md
index 3567915..1e34b44 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -658,7 +658,12 @@ clients whether chat is available for a given insight.
 
 - `POST /insights/chat` runs one turn of the agentic loop against the replayed
   history. Body: `{ file_path, library?, user_message, model?, backend?, num_ctx?,
-  temperature?, top_p?, top_k?, min_p?, max_iterations?, amend? }`.
+  temperature?, top_p?, top_k?, min_p?, max_iterations?, system_prompt?, amend? }`.
+  `system_prompt` is a per-turn override: in append mode (default) it's applied
+  ephemerally — the original system message is restored before persistence so
+  the stored transcript keeps its baked persona. In amend mode the override
+  stays in place and becomes the new insight row's system message. Mirrors the
+  internal `annotate_system_with_budget` swap-and-restore pattern.
 - `POST /insights/chat/stream` is the SSE variant — same request body, response
   is `text/event-stream` with events: `iteration_start`, `text` (delta), `tool_call`,
   `tool_result`, `truncated`, `done`, plus a server-emitted `error_message` on