[context] Store context messages in rollouts (#2243)

## Summary
Currently, we use request-time logic to determine the user_instructions
and environment_context messages. This means that neither of these
values can change over time as conversations go on. We want to add in
additional details here, so we're migrating these to save these messages
to the rollout file instead. This is simpler for the client, and allows
us to append additional environment_context messages to each turn if we
want

## Testing
- [x] Integration test coverage
- [x] Tested locally with a few turns, confirmed model could reference
environment context and cached token metrics were reasonably high

codex-rs/core/src/client_common.rs

@@ -5,15 +5,11 @@ use crate::model_family::ModelFamily;
 use crate::models::ContentItem;
 use crate::models::ResponseItem;
 use crate::openai_tools::OpenAiTool;
-use crate::protocol::AskForApproval;
-use crate::protocol::SandboxPolicy;
 use crate::protocol::TokenUsage;
 use codex_apply_patch::APPLY_PATCH_TOOL_INSTRUCTIONS;
 use futures::Stream;
 use serde::Serialize;
 use std::borrow::Cow;
-use std::fmt::Display;
-use std::path::PathBuf;
 use std::pin::Pin;
 use std::task::Context;
 use std::task::Poll;
@@ -23,62 +19,19 @@ use tokio::sync::mpsc;
 /// with this content.
 const BASE_INSTRUCTIONS: &str = include_str!("../prompt.md");
 
-/// wraps environment context message in a tag for the model to parse more easily.
-const ENVIRONMENT_CONTEXT_START: &str = "<environment_context>\n\n";
-const ENVIRONMENT_CONTEXT_END: &str = "\n\n</environment_context>";
-
 /// wraps user instructions message in a tag for the model to parse more easily.
 const USER_INSTRUCTIONS_START: &str = "<user_instructions>\n\n";
 const USER_INSTRUCTIONS_END: &str = "\n\n</user_instructions>";
 
-#[derive(Debug, Clone)]
-pub(crate) struct EnvironmentContext {
-    pub cwd: PathBuf,
-    pub approval_policy: AskForApproval,
-    pub sandbox_policy: SandboxPolicy,
-}
-
-impl Display for EnvironmentContext {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        writeln!(
-            f,
-            "Current working directory: {}",
-            self.cwd.to_string_lossy()
-        )?;
-        writeln!(f, "Approval policy: {}", self.approval_policy)?;
-        writeln!(f, "Sandbox policy: {}", self.sandbox_policy)?;
-
-        let network_access = match self.sandbox_policy.clone() {
-            SandboxPolicy::DangerFullAccess => "enabled",
-            SandboxPolicy::ReadOnly => "restricted",
-            SandboxPolicy::WorkspaceWrite { network_access, .. } => {
-                if network_access {
-                    "enabled"
-                } else {
-                    "restricted"
-                }
-            }
-        };
-        writeln!(f, "Network access: {network_access}")?;
-        Ok(())
-    }
-}
-
-/// API request payload for a single model turn.
+/// API request payload for a single model turn
 #[derive(Default, Debug, Clone)]
 pub struct Prompt {
     /// Conversation context input items.
     pub input: Vec<ResponseItem>,
-    /// Optional instructions from the user to amend to the built-in agent
-    /// instructions.
-    pub user_instructions: Option<String>,
+
     /// Whether to store response on server side (disable_response_storage = !store).
     pub store: bool,
 
-    /// A list of key-value pairs that will be added as a developer message
-    /// for the model to use
-    pub environment_context: Option<EnvironmentContext>,
-
     /// Tools available to the model, including additional tools sourced from
     /// external MCP servers.
     pub tools: Vec<OpenAiTool>,
@@ -100,36 +53,19 @@ impl Prompt {
         Cow::Owned(sections.join("\n"))
     }
 
-    fn get_formatted_user_instructions(&self) -> Option<String> {
-        self.user_instructions
-            .as_ref()
-            .map(|ui| format!("{USER_INSTRUCTIONS_START}{ui}{USER_INSTRUCTIONS_END}"))
-    }
-
-    fn get_formatted_environment_context(&self) -> Option<String> {
-        self.environment_context
-            .as_ref()
-            .map(|ec| format!("{ENVIRONMENT_CONTEXT_START}{ec}{ENVIRONMENT_CONTEXT_END}"))
-    }
-
     pub(crate) fn get_formatted_input(&self) -> Vec<ResponseItem> {
-        let mut input_with_instructions = Vec::with_capacity(self.input.len() + 2);
-        if let Some(ec) = self.get_formatted_environment_context() {
-            input_with_instructions.push(ResponseItem::Message {
-                id: None,
-                role: "user".to_string(),
-                content: vec![ContentItem::InputText { text: ec }],
-            });
+        self.input.clone()
+    }
+
+    /// Creates a formatted user instructions message from a string
+    pub(crate) fn format_user_instructions_message(ui: &str) -> ResponseItem {
+        ResponseItem::Message {
+            id: None,
+            role: "user".to_string(),
+            content: vec![ContentItem::InputText {
+                text: format!("{USER_INSTRUCTIONS_START}{ui}{USER_INSTRUCTIONS_END}"),
+            }],
         }
-        if let Some(ui) = self.get_formatted_user_instructions() {
-            input_with_instructions.push(ResponseItem::Message {
-                id: None,
-                role: "user".to_string(),
-                content: vec![ContentItem::InputText { text: ui }],
-            });
-        }
-        input_with_instructions.extend(self.input.clone());
-        input_with_instructions
     }
 }
 
@@ -259,7 +195,6 @@ mod tests {
     #[test]
     fn get_full_instructions_no_user_content() {
         let prompt = Prompt {
-            user_instructions: Some("custom instruction".to_string()),
             ..Default::default()
         };
         let expected = format!("{BASE_INSTRUCTIONS}\n{APPLY_PATCH_TOOL_INSTRUCTIONS}");