docs: clarify dcp message-id metadata tags in prompts

Author: Tarquinen

lib/prompts/compress.md

@@ -93,9 +93,12 @@ Rules:
 ID SOURCES
 
 - User messages include a text marker with their `mNNNN` ID.
-- Assistant messages include a `context_info` tool marker with their `mNNNN` ID.
+- Assistant messages usually include an XML metadata tag in the last tool output: `<dcp-message-id>mNNNN</dcp-message-id>`.
+- Assistant messages without tool outputs use a synthetic `context_info` marker instead.
 - Compressed blocks are addressable by `bN` IDs.
 
+Treat `<dcp-message-id>...</dcp-message-id>` as metadata only. It is not part of the tool result semantics.
+
 Do not invent IDs. Use only IDs that are present in context.
 
 PARALLEL COMPRESS EXECUTION

lib/prompts/system.md

@@ -23,6 +23,9 @@ Treat token counts and context growth as soft signals, not hard triggers.
 BOUNDARY MATCHING
 `compress` uses inclusive ID boundaries via `content.startId` and `content.endId`. IDs are injected in context as message refs (`mNNNN`) and compressed block refs (`bN`).
 
+Assistant tool outputs may include metadata tags like `<dcp-message-id>mNNNN</dcp-message-id>`.
+Treat these tags as boundary metadata only, not as tool result content.
+
 Only choose IDs currently visible in context. Do not invent IDs.
 
 RESPECT THE CHRONOLOGY OF THE RANGE