Fix Codex transcript streaming and images

server/src/session/driver.rs

@@ -15,6 +15,27 @@ use tokio::sync::mpsc;
 /// renders them identically.
 pub type ImageRef = String;
 
+/// Stores image bytes where the files route serves them and returns their transcript reference.
+/// Both CLI dialects produce images in different envelopes; the durable file and naming rule are
+/// part of the common event model and must not vary with that envelope.
+pub(in crate::session) fn store_image(
+    session_dir: &std::path::Path,
+    media_type: &str,
+    bytes: &[u8],
+) -> Option<ImageRef> {
+    let extension = crate::media::extension_for(media_type).unwrap_or("png");
+    let name = format!("{}.{extension}", super::random_hex());
+    let dir = session_dir.join("files");
+    if let Err(err) = wg_app_link::private::create_dir(&dir)
+        .map_err(std::io::Error::other)
+        .and_then(|()| std::fs::write(dir.join(&name), bytes))
+    {
+        tracing::error!("couldn't save produced image: {err}");
+        return None;
+    }
+    Some(name)
+}
+
 /// The name an upload is stored and served under: an image is
 /// `<hex>.<extension>` and is an [`ImageRef`] like any other; any other file
 /// keeps its own name after the hex, `<hex>-<name>`, because the name is what