feat(server): add DCP clean-room context pruning

- Deduplication: removes consecutive identical tool_call+tool_result pairs
- Purge-errors: removes failed/empty tool results
- Transform orchestrator runs strategies in sequence pre-payload
- Wired into turn.ts before buildMessagesPayload
- Clean-room reimplementation (AGPL reference: behavior only)

apps/server/src/services/inference/dcp/state.ts

@@ -0,0 +1,27 @@
+// Per-chat session state for DCP.
+// Tracks last transform timestamp and message count to avoid re-processing.
+
+interface ChatDcpState {
+  lastTransformAt: number;
+  lastMessageCount: number;
+}
+
+const chatStates = new Map<string, ChatDcpState>();
+
+export function getDcpState(chatId: string): ChatDcpState | undefined {
+  return chatStates.get(chatId);
+}
+
+export function setDcpState(chatId: string, messageCount: number): void {
+  chatStates.set(chatId, { lastTransformAt: Date.now(), lastMessageCount: messageCount });
+}
+
+export function clearDcpState(chatId: string): void {
+  chatStates.delete(chatId);
+}
+
+export function shouldTransform(chatId: string, messageCount: number): boolean {
+  const state = chatStates.get(chatId);
+  if (!state) return true;
+  return state.lastMessageCount !== messageCount;
+}