Remove the deprecated thread/rollback API (#44915)

## What changed

Remove `thread/rollback`, its request and response types, generated bindings, and the core `Op::ThreadRollback` operation. Requests now follow the generic unknown-method rejection path. Document `thread/revert` as the alternative for paginated threads.

Keep historical `ThreadRolledBack` markers and legacy error deserialization so existing rollouts remain compatible with replay and migration.

## Testing

Adapt retained-context and Guardian history tests to append legacy rollback markers and resume threads, preserving coverage of surviving instructions, answers, and review history.

GitOrigin-RevId: b3da1becdf86b1869275aacb0ffc2817cee5af2e

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

@@ -753,11 +753,6 @@ client_request_definitions! {
         serialization: thread_id(params.thread_id),
         response: v2::ThreadBackgroundTerminalsTerminateResponse,
     },
-    ThreadRollback => "thread/rollback" {
-        params: v2::ThreadRollbackParams,
-        serialization: thread_id(params.thread_id),
-        response: v2::ThreadRollbackResponse,
-    },
     ThreadRevert => "thread/revert" {
         params: v2::ThreadRevertParams,
         serialization: thread_id(params.thread_id),

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

@@ -1241,31 +1241,6 @@ pub struct ThreadBackgroundTerminalsTerminateResponse {
     pub terminated: bool,
 }
 
-#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
-#[serde(rename_all = "camelCase")]
-#[ts(export_to = "v2/")]
-/// DEPRECATED: `thread/rollback` will be removed soon.
-pub struct ThreadRollbackParams {
-    pub thread_id: String,
-    /// The number of turns to drop from the end of the thread. Must be >= 1.
-    ///
-    /// This only modifies the thread's history and does not revert local file changes
-    /// that have been made by the agent. Clients are responsible for reverting these changes.
-    pub num_turns: u32,
-}
-
-#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
-#[serde(rename_all = "camelCase")]
-#[ts(export_to = "v2/")]
-pub struct ThreadRollbackResponse {
-    /// The updated thread after applying the rollback, with `turns` populated.
-    ///
-    /// The ThreadItems stored in each Turn are lossy since we explicitly do not
-    /// persist all agent interactions, such as command executions. This is the same
-    /// behavior as `thread/resume`.
-    pub thread: Thread,
-}
-
 /// Replace a paginated thread's durable history with the prefix before one turn.
 ///
 /// This only changes persisted conversation history. It does not revert local file changes.

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

@@ -286,7 +286,7 @@ pub struct Thread {
     /// Saved Daybreak choice, independent of turn execution. Null if unset.
     #[experimental("thread.daybreakEnabled")]
     pub daybreak_enabled: Option<bool>,
-    /// Only populated on `thread/resume`, `thread/rollback`, `thread/fork`, and `thread/read`
+    /// Only populated on `thread/resume`, `thread/fork`, and `thread/read`
     /// (when `includeTurns` is true) responses.
     /// For all other responses and notifications returning a Thread,
     /// the turns field will be an empty list.