feat: add Responses compaction support

TERMINOLOGY.md

@@ -129,6 +129,29 @@ Describes a flow in which the service retains or resolves prior state, such as R
 Describes a flow in which the request supplies all required context and the service does not rely on retained response
 or conversation state. `store: false` disables stored-response state, although callers may still replay prior items.
 
+### compaction
+
+Replacing a long item history with a smaller canonical window that preserves user messages and a model-generated
+summary. Compaction is distinct from truncation: it uses an inference call to summarize context rather than silently
+dropping items.
+
+### compaction item
+
+An item with `type: "compaction"` whose `encrypted_content` carries the context checkpoint consumed by a later model
+request. Preserve the exact field name in wire-format discussion. In this project's local implementation the field is
+plaintext despite its protocol name.
+
+### compacted window
+
+The canonical output of a compaction request: retained user-message items followed by one compaction item. Replay the
+complete window as later Responses input; do not extract only the summary.
+
+### context management
+
+The Responses request policy expressed by `context_management`. A `type: "compaction"` entry with
+`compact_threshold` asks the gateway to compact resolved input before inference when its estimated token count exceeds
+the threshold.
+
 ## Tools and tool calling
 
 ### tool
@@ -340,3 +363,4 @@ These definitions follow current OpenAI documentation:
 - [MCP and Connectors](https://developers.openai.com/api/docs/guides/tools-connectors-mcp)
 - [Streaming API responses](https://developers.openai.com/api/docs/guides/streaming-responses)
 - [Reasoning models](https://developers.openai.com/api/docs/guides/reasoning)
+- [Compaction](https://developers.openai.com/api/docs/guides/compaction)

crates/agentic-server-core/benches/executor_throughput.rs

@@ -147,6 +147,7 @@ fn make_request(input: &str, stream: bool, prev_id: Option<String>) -> RequestPa
         metadata: None,
         parallel_tool_calls: None,
         cache_salt: None,
+        context_management: None,
     }
 }
 

crates/agentic-server-core/benches/storage_concurrent.rs

@@ -61,7 +61,9 @@ fn next_id() -> String {
 
 fn make_items() -> Vec<InOutItem> {
     let input = InputItem::Message(InputMessage {
+        id: None,
         role: "user".to_string(),
+        status: None,
         content: InputMessageContent::Text("Test message".to_string()),
     });
     vec![

crates/agentic-server-core/benches/storage_crud.rs

@@ -13,7 +13,9 @@ fn next_id() -> String {
 
 fn create_test_items() -> Vec<InOutItem> {
     let input_item = InputItem::Message(InputMessage {
+        id: None,
         role: "user".to_string(),
+        status: None,
         content: InputMessageContent::Text("Test message".to_string()),
     });