Remove ghost snapshots (#19481)

## Summary
- Remove `ghost_snapshot` / `GhostCommit` from the Responses API surface
and generated SDK/schema artifacts.
- Keep legacy config loading compatible, but make undo a no-op that
reports the feature is unavailable.
- Clean up core history, compaction, telemetry, rollout, and tests to
stop carrying ghost snapshot items.

## Testing
- Unit tests passed for `codex-protocol`, `codex-core` targeted undo and
compaction flows, `codex-rollout`, and `codex-app-server-protocol`.
- Regenerated config and app-server schemas plus Python SDK artifacts
and verified they match the checked-in outputs.

codex-rs/protocol/src/models.rs

@@ -1,9 +1,7 @@
 use std::collections::HashMap;
-use std::fmt;
 use std::io;
 use std::num::NonZeroUsize;
 use std::path::Path;
-use std::path::PathBuf;
 
 use codex_utils_image::PromptImageMode;
 use codex_utils_image::load_for_prompt_bytes;
@@ -28,60 +26,6 @@ use schemars::JsonSchema;
 
 use crate::mcp::CallToolResult;
 
-type CommitID = String;
-
-/// Details of a ghost commit created from a repository state.
-#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, JsonSchema, TS)]
-pub struct GhostCommit {
-    id: CommitID,
-    parent: Option<CommitID>,
-    preexisting_untracked_files: Vec<PathBuf>,
-    preexisting_untracked_dirs: Vec<PathBuf>,
-}
-
-impl GhostCommit {
-    /// Create a new ghost commit wrapper from a raw commit ID and optional parent.
-    pub fn new(
-        id: CommitID,
-        parent: Option<CommitID>,
-        preexisting_untracked_files: Vec<PathBuf>,
-        preexisting_untracked_dirs: Vec<PathBuf>,
-    ) -> Self {
-        Self {
-            id,
-            parent,
-            preexisting_untracked_files,
-            preexisting_untracked_dirs,
-        }
-    }
-
-    /// Commit ID for the snapshot.
-    pub fn id(&self) -> &str {
-        &self.id
-    }
-
-    /// Parent commit ID, if the repository had a `HEAD` at creation time.
-    pub fn parent(&self) -> Option<&str> {
-        self.parent.as_deref()
-    }
-
-    /// Untracked or ignored files that already existed when the snapshot was captured.
-    pub fn preexisting_untracked_files(&self) -> &[PathBuf] {
-        &self.preexisting_untracked_files
-    }
-
-    /// Untracked or ignored directories that already existed when the snapshot was captured.
-    pub fn preexisting_untracked_dirs(&self) -> &[PathBuf] {
-        &self.preexisting_untracked_dirs
-    }
-}
-
-impl fmt::Display for GhostCommit {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}", self.id)
-    }
-}
-
 /// Controls the per-command sandbox override requested by a shell-like tool call.
 #[derive(
     Debug, Clone, Copy, Default, Eq, Hash, PartialEq, Serialize, Deserialize, JsonSchema, TS,
@@ -879,14 +823,8 @@ pub enum ResponseItem {
         revised_prompt: Option<String>,
         result: String,
     },
-    // Generated by the harness but considered exactly as a model response.
-    GhostSnapshot {
-        ghost_commit: GhostCommit,
-    },
     #[serde(alias = "compaction_summary")]
-    Compaction {
-        encrypted_content: String,
-    },
+    Compaction { encrypted_content: String },
     #[serde(other)]
     Other,
 }
@@ -1640,6 +1578,7 @@ mod tests {
     use anyhow::Result;
     use codex_execpolicy::Policy;
     use pretty_assertions::assert_eq;
+    use std::path::PathBuf;
     use tempfile::tempdir;
 
     #[test]
@@ -2380,6 +2319,24 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn deserializes_legacy_ghost_snapshot_as_other() -> Result<()> {
+        let json = r#"{
+            "type":"ghost_snapshot",
+            "ghost_commit":{
+                "id":"ghost-1",
+                "parent":null,
+                "preexisting_untracked_files":[],
+                "preexisting_untracked_dirs":[]
+            }
+        }"#;
+
+        let item: ResponseItem = serde_json::from_str(json)?;
+
+        assert_eq!(item, ResponseItem::Other);
+        Ok(())
+    }
+
     #[test]
     fn roundtrips_web_search_call_actions() -> Result<()> {
         let cases = vec![

codex-rs/protocol/src/protocol.rs

@@ -775,7 +775,10 @@ pub enum Op {
     /// model.
     SetThreadMemoryMode { mode: ThreadMemoryMode },
 
-    /// Request Codex to undo a turn (turn are stacked so it is the same effect as CMD + Z).
+    /// Legacy request to undo a turn.
+    ///
+    /// The op is still accepted for compatibility, but ghost snapshots are no
+    /// longer produced so the request reports unavailable.
     Undo,
 
     /// Request Codex to drop the last N user turns from in-memory context.