Add thread compact start v2 RPC and fixtures

codex-rs/app-server-protocol/schema/json/ClientRequest.json

@@ -2235,6 +2235,17 @@
       ],
       "type": "object"
     },
+    "ThreadCompactStartParams": {
+      "properties": {
+        "threadId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "threadId"
+      ],
+      "type": "object"
+    },
     "ThreadForkParams": {
       "description": "There are two ways to fork a thread: 1. By thread_id: load the thread from disk by thread_id and fork it into a new thread. 2. By path: load the thread from disk by path and fork it into a new thread.\n\nIf using path, the thread_id param will be ignored.\n\nPrefer using thread_id whenever possible.",
       "properties": {
@@ -3210,6 +3221,30 @@
       "title": "Thread/unarchiveRequest",
       "type": "object"
     },
+    {
+      "properties": {
+        "id": {
+          "$ref": "#/definitions/RequestId"
+        },
+        "method": {
+          "enum": [
+            "thread/compact/start"
+          ],
+          "title": "Thread/compact/startRequestMethod",
+          "type": "string"
+        },
+        "params": {
+          "$ref": "#/definitions/ThreadCompactStartParams"
+        }
+      },
+      "required": [
+        "id",
+        "method",
+        "params"
+      ],
+      "title": "Thread/compact/startRequest",
+      "type": "object"
+    },
     {
       "properties": {
         "id": {

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -598,6 +598,30 @@
           "title": "Thread/unarchiveRequest",
           "type": "object"
         },
+        {
+          "properties": {
+            "id": {
+              "$ref": "#/definitions/RequestId"
+            },
+            "method": {
+              "enum": [
+                "thread/compact/start"
+              ],
+              "title": "Thread/compact/startRequestMethod",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/definitions/v2/ThreadCompactStartParams"
+            }
+          },
+          "required": [
+            "id",
+            "method",
+            "params"
+          ],
+          "title": "Thread/compact/startRequest",
+          "type": "object"
+        },
         {
           "properties": {
             "id": {
@@ -13855,6 +13879,24 @@
         "title": "ThreadArchiveResponse",
         "type": "object"
       },
+      "ThreadCompactStartParams": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "properties": {
+          "threadId": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "threadId"
+        ],
+        "title": "ThreadCompactStartParams",
+        "type": "object"
+      },
+      "ThreadCompactStartResponse": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "ThreadCompactStartResponse",
+        "type": "object"
+      },
       "ThreadForkParams": {
         "$schema": "http://json-schema.org/draft-07/schema#",
         "description": "There are two ways to fork a thread: 1. By thread_id: load the thread from disk by thread_id and fork it into a new thread. 2. By path: load the thread from disk by path and fork it into a new thread.\n\nIf using path, the thread_id param will be ignored.\n\nPrefer using thread_id whenever possible.",

codex-rs/app-server-protocol/schema/json/v2/ThreadCompactStartParams.json

@@ -0,0 +1,13 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "properties": {
+    "threadId": {
+      "type": "string"
+    }
+  },
+  "required": [
+    "threadId"
+  ],
+  "title": "ThreadCompactStartParams",
+  "type": "object"
+}

codex-rs/app-server-protocol/schema/json/v2/ThreadCompactStartResponse.json

@@ -0,0 +1,5 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "ThreadCompactStartResponse",
+  "type": "object"
+}

codex-rs/app-server-protocol/schema/typescript/ClientRequest.ts

@@ -39,6 +39,7 @@ import type { SkillsListParams } from "./v2/SkillsListParams";
 import type { SkillsRemoteReadParams } from "./v2/SkillsRemoteReadParams";
 import type { SkillsRemoteWriteParams } from "./v2/SkillsRemoteWriteParams";
 import type { ThreadArchiveParams } from "./v2/ThreadArchiveParams";
+import type { ThreadCompactStartParams } from "./v2/ThreadCompactStartParams";
 import type { ThreadForkParams } from "./v2/ThreadForkParams";
 import type { ThreadListParams } from "./v2/ThreadListParams";
 import type { ThreadLoadedListParams } from "./v2/ThreadLoadedListParams";
@@ -54,4 +55,4 @@ import type { TurnStartParams } from "./v2/TurnStartParams";
 /**
  * Request from the client to the server.
  */
-export type ClientRequest ={ "method": "initialize", id: RequestId, params: InitializeParams, } | { "method": "thread/start", id: RequestId, params: ThreadStartParams, } | { "method": "thread/resume", id: RequestId, params: ThreadResumeParams, } | { "method": "thread/fork", id: RequestId, params: ThreadForkParams, } | { "method": "thread/archive", id: RequestId, params: ThreadArchiveParams, } | { "method": "thread/name/set", id: RequestId, params: ThreadSetNameParams, } | { "method": "thread/unarchive", id: RequestId, params: ThreadUnarchiveParams, } | { "method": "thread/rollback", id: RequestId, params: ThreadRollbackParams, } | { "method": "thread/list", id: RequestId, params: ThreadListParams, } | { "method": "thread/loaded/list", id: RequestId, params: ThreadLoadedListParams, } | { "method": "thread/read", id: RequestId, params: ThreadReadParams, } | { "method": "skills/list", id: RequestId, params: SkillsListParams, } | { "method": "skills/remote/read", id: RequestId, params: SkillsRemoteReadParams, } | { "method": "skills/remote/write", id: RequestId, params: SkillsRemoteWriteParams, } | { "method": "app/list", id: RequestId, params: AppsListParams, } | { "method": "skills/config/write", id: RequestId, params: SkillsConfigWriteParams, } | { "method": "turn/start", id: RequestId, params: TurnStartParams, } | { "method": "turn/interrupt", id: RequestId, params: TurnInterruptParams, } | { "method": "review/start", id: RequestId, params: ReviewStartParams, } | { "method": "model/list", id: RequestId, params: ModelListParams, } | { "method": "mcpServer/oauth/login", id: RequestId, params: McpServerOauthLoginParams, } | { "method": "config/mcpServer/reload", id: RequestId, params: undefined, } | { "method": "mcpServerStatus/list", id: RequestId, params: ListMcpServerStatusParams, } | { "method": "account/login/start", id: RequestId, params: LoginAccountParams, } | { "method": "account/login/cancel", id: RequestId, params: CancelLoginAccountParams, } | { "method": "account/logout", id: RequestId, params: undefined, } | { "method": "account/rateLimits/read", id: RequestId, params: undefined, } | { "method": "feedback/upload", id: RequestId, params: FeedbackUploadParams, } | { "method": "command/exec", id: RequestId, params: CommandExecParams, } | { "method": "config/read", id: RequestId, params: ConfigReadParams, } | { "method": "config/value/write", id: RequestId, params: ConfigValueWriteParams, } | { "method": "config/batchWrite", id: RequestId, params: ConfigBatchWriteParams, } | { "method": "configRequirements/read", id: RequestId, params: undefined, } | { "method": "account/read", id: RequestId, params: GetAccountParams, } | { "method": "newConversation", id: RequestId, params: NewConversationParams, } | { "method": "getConversationSummary", id: RequestId, params: GetConversationSummaryParams, } | { "method": "listConversations", id: RequestId, params: ListConversationsParams, } | { "method": "resumeConversation", id: RequestId, params: ResumeConversationParams, } | { "method": "forkConversation", id: RequestId, params: ForkConversationParams, } | { "method": "archiveConversation", id: RequestId, params: ArchiveConversationParams, } | { "method": "sendUserMessage", id: RequestId, params: SendUserMessageParams, } | { "method": "sendUserTurn", id: RequestId, params: SendUserTurnParams, } | { "method": "interruptConversation", id: RequestId, params: InterruptConversationParams, } | { "method": "addConversationListener", id: RequestId, params: AddConversationListenerParams, } | { "method": "removeConversationListener", id: RequestId, params: RemoveConversationListenerParams, } | { "method": "gitDiffToRemote", id: RequestId, params: GitDiffToRemoteParams, } | { "method": "loginApiKey", id: RequestId, params: LoginApiKeyParams, } | { "method": "loginChatGpt", id: RequestId, params: undefined, } | { "method": "cancelLoginChatGpt", id: RequestId, params: CancelLoginChatGptParams, } | { "method": "logoutChatGpt", id: RequestId, params: undefined, } | { "method": "getAuthStatus", id: RequestId, params: GetAuthStatusParams, } | { "method": "getUserSavedConfig", id: RequestId, params: undefined, } | { "method": "setDefaultModel", id: RequestId, params: SetDefaultModelParams, } | { "method": "getUserAgent", id: RequestId, params: undefined, } | { "method": "userInfo", id: RequestId, params: undefined, } | { "method": "fuzzyFileSearch", id: RequestId, params: FuzzyFileSearchParams, } | { "method": "execOneOffCommand", id: RequestId, params: ExecOneOffCommandParams, };
+export type ClientRequest ={ "method": "initialize", id: RequestId, params: InitializeParams, } | { "method": "thread/start", id: RequestId, params: ThreadStartParams, } | { "method": "thread/resume", id: RequestId, params: ThreadResumeParams, } | { "method": "thread/fork", id: RequestId, params: ThreadForkParams, } | { "method": "thread/archive", id: RequestId, params: ThreadArchiveParams, } | { "method": "thread/name/set", id: RequestId, params: ThreadSetNameParams, } | { "method": "thread/unarchive", id: RequestId, params: ThreadUnarchiveParams, } | { "method": "thread/compact/start", id: RequestId, params: ThreadCompactStartParams, } | { "method": "thread/rollback", id: RequestId, params: ThreadRollbackParams, } | { "method": "thread/list", id: RequestId, params: ThreadListParams, } | { "method": "thread/loaded/list", id: RequestId, params: ThreadLoadedListParams, } | { "method": "thread/read", id: RequestId, params: ThreadReadParams, } | { "method": "skills/list", id: RequestId, params: SkillsListParams, } | { "method": "skills/remote/read", id: RequestId, params: SkillsRemoteReadParams, } | { "method": "skills/remote/write", id: RequestId, params: SkillsRemoteWriteParams, } | { "method": "app/list", id: RequestId, params: AppsListParams, } | { "method": "skills/config/write", id: RequestId, params: SkillsConfigWriteParams, } | { "method": "turn/start", id: RequestId, params: TurnStartParams, } | { "method": "turn/interrupt", id: RequestId, params: TurnInterruptParams, } | { "method": "review/start", id: RequestId, params: ReviewStartParams, } | { "method": "model/list", id: RequestId, params: ModelListParams, } | { "method": "mcpServer/oauth/login", id: RequestId, params: McpServerOauthLoginParams, } | { "method": "config/mcpServer/reload", id: RequestId, params: undefined, } | { "method": "mcpServerStatus/list", id: RequestId, params: ListMcpServerStatusParams, } | { "method": "account/login/start", id: RequestId, params: LoginAccountParams, } | { "method": "account/login/cancel", id: RequestId, params: CancelLoginAccountParams, } | { "method": "account/logout", id: RequestId, params: undefined, } | { "method": "account/rateLimits/read", id: RequestId, params: undefined, } | { "method": "feedback/upload", id: RequestId, params: FeedbackUploadParams, } | { "method": "command/exec", id: RequestId, params: CommandExecParams, } | { "method": "config/read", id: RequestId, params: ConfigReadParams, } | { "method": "config/value/write", id: RequestId, params: ConfigValueWriteParams, } | { "method": "config/batchWrite", id: RequestId, params: ConfigBatchWriteParams, } | { "method": "configRequirements/read", id: RequestId, params: undefined, } | { "method": "account/read", id: RequestId, params: GetAccountParams, } | { "method": "newConversation", id: RequestId, params: NewConversationParams, } | { "method": "getConversationSummary", id: RequestId, params: GetConversationSummaryParams, } | { "method": "listConversations", id: RequestId, params: ListConversationsParams, } | { "method": "resumeConversation", id: RequestId, params: ResumeConversationParams, } | { "method": "forkConversation", id: RequestId, params: ForkConversationParams, } | { "method": "archiveConversation", id: RequestId, params: ArchiveConversationParams, } | { "method": "sendUserMessage", id: RequestId, params: SendUserMessageParams, } | { "method": "sendUserTurn", id: RequestId, params: SendUserTurnParams, } | { "method": "interruptConversation", id: RequestId, params: InterruptConversationParams, } | { "method": "addConversationListener", id: RequestId, params: AddConversationListenerParams, } | { "method": "removeConversationListener", id: RequestId, params: RemoveConversationListenerParams, } | { "method": "gitDiffToRemote", id: RequestId, params: GitDiffToRemoteParams, } | { "method": "loginApiKey", id: RequestId, params: LoginApiKeyParams, } | { "method": "loginChatGpt", id: RequestId, params: undefined, } | { "method": "cancelLoginChatGpt", id: RequestId, params: CancelLoginChatGptParams, } | { "method": "logoutChatGpt", id: RequestId, params: undefined, } | { "method": "getAuthStatus", id: RequestId, params: GetAuthStatusParams, } | { "method": "getUserSavedConfig", id: RequestId, params: undefined, } | { "method": "setDefaultModel", id: RequestId, params: SetDefaultModelParams, } | { "method": "getUserAgent", id: RequestId, params: undefined, } | { "method": "userInfo", id: RequestId, params: undefined, } | { "method": "fuzzyFileSearch", id: RequestId, params: FuzzyFileSearchParams, } | { "method": "execOneOffCommand", id: RequestId, params: ExecOneOffCommandParams, };

codex-rs/app-server-protocol/schema/typescript/v2/ThreadCompactStartParams.ts

@@ -0,0 +1,5 @@
+// GENERATED CODE! DO NOT MODIFY BY HAND!
+
+// This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
+
+export type ThreadCompactStartParams = { threadId: string, };

codex-rs/app-server-protocol/schema/typescript/v2/ThreadCompactStartResponse.ts

@@ -0,0 +1,5 @@
+// GENERATED CODE! DO NOT MODIFY BY HAND!
+
+// This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
+
+export type ThreadCompactStartResponse = Record<string, never>;

codex-rs/app-server-protocol/schema/typescript/v2/index.ts

@@ -128,6 +128,8 @@ export type { TextRange } from "./TextRange";
 export type { Thread } from "./Thread";
 export type { ThreadArchiveParams } from "./ThreadArchiveParams";
 export type { ThreadArchiveResponse } from "./ThreadArchiveResponse";
+export type { ThreadCompactStartParams } from "./ThreadCompactStartParams";
+export type { ThreadCompactStartResponse } from "./ThreadCompactStartResponse";
 export type { ThreadForkParams } from "./ThreadForkParams";
 export type { ThreadForkResponse } from "./ThreadForkResponse";
 export type { ThreadItem } from "./ThreadItem";

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -208,6 +208,10 @@ client_request_definitions! {
         params: v2::ThreadUnarchiveParams,
         response: v2::ThreadUnarchiveResponse,
     },
+    ThreadCompactStart => "thread/compact/start" {
+        params: v2::ThreadCompactStartParams,
+        response: v2::ThreadCompactStartResponse,
+    },
     ThreadRollback => "thread/rollback" {
         params: v2::ThreadRollbackParams,
         response: v2::ThreadRollbackResponse,

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -1408,6 +1408,18 @@ pub struct ThreadUnarchiveResponse {
     pub thread: Thread,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ThreadCompactStartParams {
+    pub thread_id: String,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ThreadCompactStartResponse {}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]

codex-rs/app-server/README.md

@@ -85,6 +85,7 @@ Example (from OpenAI's official VSCode extension):
 - `thread/archive` — move a thread’s rollout file into the archived directory; returns `{}` on success.
 - `thread/name/set` — set or update a thread’s user-facing name; returns `{}` on success. Thread names are not required to be unique; name lookups resolve to the most recently updated thread.
 - `thread/unarchive` — move an archived rollout file back into the sessions directory; returns the restored `thread` on success.
+- `thread/compact/start` — trigger conversation history compaction for a thread; returns `{}` immediately while progress streams through standard turn/item notifications.
 - `thread/rollback` — drop the last N turns from the agent’s in-memory context and persist a rollback marker in the rollout so future resumes see the pruned history; returns the updated `thread` (with `turns` populated) on success.
 - `turn/start` — add user input to a thread and begin Codex generation; responds with the initial `turn` object and streams `turn/started`, `item/*`, and `turn/completed` notifications.
 - `turn/interrupt` — request cancellation of an in-flight turn by `(thread_id, turn_id)`; success is an empty `{}` response and the turn finishes with `status: "interrupted"`.
@@ -239,6 +240,22 @@ Use `thread/unarchive` to move an archived rollout back into the sessions direct
 { "id": 24, "result": { "thread": { "id": "thr_b" } } }
 ```
 
+### Example: Trigger thread compaction
+
+Use `thread/compact/start` to trigger manual history compaction for a thread. The request returns immediately with `{}`.
+
+Progress is emitted as standard `turn/*` and `item/*` notifications on the same `threadId`. Clients should expect a single compaction item:
+
+- `item/started` with `item: { "type": "contextCompaction", ... }`
+- `item/completed` with the same `contextCompaction` item id
+
+While compaction is running, the thread is effectively in a turn so clients should surface progress UI based on the notifications.
+
+```json
+{ "method": "thread/compact/start", "id": 25, "params": { "threadId": "thr_b" } }
+{ "id": 25, "result": {} }
+```
+
 ### Example: Start a turn (send user input)
 
 Turns attach user input (text or images) to a thread and trigger Codex generation. The `input` field is a list of discriminated unions:

codex-rs/app-server/src/codex_message_processor.rs

@@ -104,6 +104,8 @@ use codex_app_server_protocol::SkillsRemoteWriteResponse;
 use codex_app_server_protocol::Thread;
 use codex_app_server_protocol::ThreadArchiveParams;
 use codex_app_server_protocol::ThreadArchiveResponse;
+use codex_app_server_protocol::ThreadCompactStartParams;
+use codex_app_server_protocol::ThreadCompactStartResponse;
 use codex_app_server_protocol::ThreadForkParams;
 use codex_app_server_protocol::ThreadForkResponse;
 use codex_app_server_protocol::ThreadItem;
@@ -455,6 +457,9 @@ impl CodexMessageProcessor {
             ClientRequest::ThreadUnarchive { request_id, params } => {
                 self.thread_unarchive(request_id, params).await;
             }
+            ClientRequest::ThreadCompactStart { request_id, params } => {
+                self.thread_compact_start(request_id, params).await;
+            }
             ClientRequest::ThreadRollback { request_id, params } => {
                 self.thread_rollback(request_id, params).await;
             }
@@ -2094,6 +2099,30 @@ impl CodexMessageProcessor {
         }
     }
 
+    async fn thread_compact_start(&self, request_id: RequestId, params: ThreadCompactStartParams) {
+        let ThreadCompactStartParams { thread_id } = params;
+
+        let (_, thread) = match self.load_thread(&thread_id).await {
+            Ok(v) => v,
+            Err(error) => {
+                self.outgoing.send_error(request_id, error).await;
+                return;
+            }
+        };
+
+        match thread.submit(Op::Compact).await {
+            Ok(_) => {
+                self.outgoing
+                    .send_response(request_id, ThreadCompactStartResponse {})
+                    .await;
+            }
+            Err(err) => {
+                self.send_internal_error(request_id, format!("failed to start compaction: {err}"))
+                    .await;
+            }
+        }
+    }
+
     async fn thread_list(&self, request_id: RequestId, params: ThreadListParams) {
         let ThreadListParams {
             cursor,

codex-rs/app-server/tests/common/mcp_process.rs

@@ -50,6 +50,7 @@ use codex_app_server_protocol::SendUserTurnParams;
 use codex_app_server_protocol::ServerRequest;
 use codex_app_server_protocol::SetDefaultModelParams;
 use codex_app_server_protocol::ThreadArchiveParams;
+use codex_app_server_protocol::ThreadCompactStartParams;
 use codex_app_server_protocol::ThreadForkParams;
 use codex_app_server_protocol::ThreadListParams;
 use codex_app_server_protocol::ThreadLoadedListParams;
@@ -418,6 +419,15 @@ impl McpProcess {
         self.send_request("thread/unarchive", params).await
     }
 
+    /// Send a `thread/compact/start` JSON-RPC request.
+    pub async fn send_thread_compact_start_request(
+        &mut self,
+        params: ThreadCompactStartParams,
+    ) -> anyhow::Result<i64> {
+        let params = Some(serde_json::to_value(params)?);
+        self.send_request("thread/compact/start", params).await
+    }
+
     /// Send a `thread/rollback` JSON-RPC request.
     pub async fn send_thread_rollback_request(
         &mut self,

codex-rs/app-server/tests/suite/v2/compaction.rs

@@ -15,9 +15,12 @@ use app_test_support::write_chatgpt_auth;
 use app_test_support::write_mock_responses_config_toml;
 use codex_app_server_protocol::ItemCompletedNotification;
 use codex_app_server_protocol::ItemStartedNotification;
+use codex_app_server_protocol::JSONRPCError;
 use codex_app_server_protocol::JSONRPCNotification;
 use codex_app_server_protocol::JSONRPCResponse;
 use codex_app_server_protocol::RequestId;
+use codex_app_server_protocol::ThreadCompactStartParams;
+use codex_app_server_protocol::ThreadCompactStartResponse;
 use codex_app_server_protocol::ThreadItem;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
@@ -39,6 +42,7 @@ use tokio::time::timeout;
 const DEFAULT_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10);
 const AUTO_COMPACT_LIMIT: i64 = 1_000;
 const COMPACT_PROMPT: &str = "Summarize the conversation.";
+const INVALID_REQUEST_ERROR_CODE: i64 = -32600;
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn auto_compaction_local_emits_started_and_completed_items() -> Result<()> {
@@ -196,6 +200,134 @@ async fn auto_compaction_remote_emits_started_and_completed_items() -> Result<()
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn thread_compact_start_triggers_compaction_and_returns_empty_response() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let sse = responses::sse(vec![
+        responses::ev_assistant_message("m1", "MANUAL_COMPACT_SUMMARY"),
+        responses::ev_completed_with_tokens("r1", 200),
+    ]);
+    responses::mount_sse_sequence(&server, vec![sse]).await;
+
+    let codex_home = TempDir::new()?;
+    write_mock_responses_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        &BTreeMap::default(),
+        AUTO_COMPACT_LIMIT,
+        None,
+        "mock_provider",
+        COMPACT_PROMPT,
+    )?;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
+
+    let thread_id = start_thread(&mut mcp).await?;
+    let compact_id = mcp
+        .send_thread_compact_start_request(ThreadCompactStartParams {
+            thread_id: thread_id.clone(),
+        })
+        .await?;
+    let compact_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(compact_id)),
+    )
+    .await??;
+    let _compact: ThreadCompactStartResponse =
+        to_response::<ThreadCompactStartResponse>(compact_resp)?;
+
+    let started = wait_for_context_compaction_started(&mut mcp).await?;
+    let completed = wait_for_context_compaction_completed(&mut mcp).await?;
+
+    let ThreadItem::ContextCompaction { id: started_id } = started.item else {
+        unreachable!("started item should be context compaction");
+    };
+    let ThreadItem::ContextCompaction { id: completed_id } = completed.item else {
+        unreachable!("completed item should be context compaction");
+    };
+
+    assert_eq!(started.thread_id, thread_id);
+    assert_eq!(completed.thread_id, thread_id);
+    assert_eq!(started_id, completed_id);
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn thread_compact_start_rejects_invalid_thread_id() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let codex_home = TempDir::new()?;
+    write_mock_responses_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        &BTreeMap::default(),
+        AUTO_COMPACT_LIMIT,
+        None,
+        "mock_provider",
+        COMPACT_PROMPT,
+    )?;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
+
+    let request_id = mcp
+        .send_thread_compact_start_request(ThreadCompactStartParams {
+            thread_id: "not-a-thread-id".to_string(),
+        })
+        .await?;
+    let error: JSONRPCError = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_error_message(RequestId::Integer(request_id)),
+    )
+    .await??;
+
+    assert_eq!(error.error.code, INVALID_REQUEST_ERROR_CODE);
+    assert!(error.error.message.contains("invalid thread id"));
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn thread_compact_start_rejects_unknown_thread_id() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let codex_home = TempDir::new()?;
+    write_mock_responses_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        &BTreeMap::default(),
+        AUTO_COMPACT_LIMIT,
+        None,
+        "mock_provider",
+        COMPACT_PROMPT,
+    )?;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
+
+    let request_id = mcp
+        .send_thread_compact_start_request(ThreadCompactStartParams {
+            thread_id: "67e55044-10b1-426f-9247-bb680e5fe0c8".to_string(),
+        })
+        .await?;
+    let error: JSONRPCError = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_error_message(RequestId::Integer(request_id)),
+    )
+    .await??;
+
+    assert_eq!(error.error.code, INVALID_REQUEST_ERROR_CODE);
+    assert!(error.error.message.contains("thread not found"));
+
+    Ok(())
+}
+
 async fn start_thread(mcp: &mut McpProcess) -> Result<String> {
     let thread_id = mcp
         .send_thread_start_request(ThreadStartParams {