Tell the model when a message was a steer

A message typed during a turn reaches the model at the next model call if
the turn has one left, and otherwise as the opening line of the next turn --
Claude's read out of the fifo after the turn ended, Codex's requeued when
turn/steer is refused. Read there it is indistinguishable from a reply, so
the model treats the answer it just gave as seen.

Both drivers now compose the text the CLI receives through
driver::message_body, which prefixes a note saying the message was written
without having seen the rest of that turn. The transcript still holds the
words that were typed; only the CLI's copy carries the note.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

server/src/session/codex.rs

@@ -44,6 +44,14 @@ struct Waiting {
     /// The id Codex echoes on its user-message item.
     #[serde(default)]
     client_id: String,
+    /// Typed while a turn was already running, so the CLI is told as much --
+    /// see `super::driver::message_body`. Recorded at the moment it was typed
+    /// rather than read off the turn state when it is dispatched, because a
+    /// steer Codex refuses as `activeTurnNotSteerable` is requeued and sent as
+    /// the start of the next turn, which is precisely the case the note exists
+    /// for.
+    #[serde(default)]
+    steering: bool,
     text: String,
     #[serde(default)]
     attachments: Vec<AttachmentRef>,
@@ -202,10 +210,12 @@ impl Driver for CodexDriver {
             return;
         }
         let id = state.running.then(super::random_hex).unwrap_or_default();
+        let steering = state.running;
         state.running = true;
         state.waiting.push_back(Waiting {
             id: id.clone(),
             client_id: format!("ai-app-{}", super::random_hex()),
+            steering,
             text: text.clone(),
             attachments: attachments.clone(),
         });
@@ -463,7 +473,7 @@ fn sandbox_policy(mode: &str) -> Value {
 }
 
 fn input_for(inner: &Inner, message: &Waiting) -> Result<Vec<Value>> {
-    let mut text = message.text.clone();
+    let mut files = Vec::new();
     let mut input = Vec::new();
     for attachment in &message.attachments {
         let path = attachment_path(&inner.session_dir, attachment)?;
@@ -477,12 +487,10 @@ fn input_for(inner: &Inner, message: &Waiting) -> Result<Vec<Value>> {
                 input.push(inline_image(&path, media_type)?);
             }
         } else {
-            if !text.is_empty() {
-                text.push_str("\n\n");
-            }
-            text.push_str(&format!("Attached file: {}", path.display()));
+            files.push(path);
         }
     }
+    let text = super::driver::message_body(&message.text, &files, message.steering);
     if !text.is_empty() {
         input.insert(0, json!({"type": "text", "text": text}));
     }