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/transform.ts

@@ -0,0 +1,52 @@
+// Transform orchestrator — runs DCP strategies in sequence.
+// Clean-room implementation.
+
+import type { DcpMessage } from './messages.js';
+import { deduplicate } from './strategies/deduplication.js';
+import { purgeErrors } from './strategies/purge-errors.js';
+import { getDcpState, setDcpState, shouldTransform } from './state.js';
+
+export interface TransformStats {
+  removedCount: number;
+  freedTokens: number;
+  dedupRemoved: number;
+  purgeRemoved: number;
+}
+
+export interface TransformResult {
+  messages: DcpMessage[];
+  stats: TransformStats;
+}
+
+export function transformMessages(chatId: string, messages: DcpMessage[]): TransformResult {
+  if (!shouldTransform(chatId, messages.length)) {
+    return { messages, stats: { removedCount: 0, freedTokens: 0, dedupRemoved: 0, purgeRemoved: 0 } };
+  }
+
+  let m = messages;
+
+  // Step 1: Deduplicate
+  const dedupResult = deduplicate(m);
+  m = dedupResult.messages;
+  const dedupRemoved = dedupResult.stats.removedCount;
+
+  // Step 2: Purge errors
+  const purgeResult = purgeErrors(m);
+  m = purgeResult.messages;
+  const purgeRemoved = purgeResult.stats.removedCount;
+
+  const totalRemoved = dedupRemoved + purgeRemoved;
+  const totalFreed = dedupResult.stats.freedTokens + purgeResult.stats.freedTokens;
+
+  setDcpState(chatId, messages.length);
+
+  return {
+    messages: m,
+    stats: {
+      removedCount: totalRemoved,
+      freedTokens: totalFreed,
+      dedupRemoved,
+      purgeRemoved,
+    },
+  };
+}