fix chat streaming and prompt writes

- Return chat file as text/plain to preserve line ordering
- Fix handleWrite: single-key JSON writes raw value, not key=value
- Fixes broken chat display and 'prompt=' corruption in chat log

main.go

@@ -218,6 +218,11 @@ func handleRead(w http.ResponseWriter, fsys *client.Fsys, p string) {
 		writeJSON(w, http.StatusOK, parseIdx(content))
 		return
 	}
+	if path.Base(p) == "chat" {
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		w.Write(content)
+		return
+	}
 	writeJSON(w, http.StatusOK, parseContent(content, path.Base(p)))
 }
 
@@ -318,12 +323,24 @@ func handleWrite(w http.ResponseWriter, r *http.Request, fsys *client.Fsys, p st
 		writeJSON(w, http.StatusBadRequest, map[string]string{"error": err.Error()})
 		return
 	}
+	// If the body has a single key matching the file name, write just the value.
+	// Otherwise serialize as key=value lines (e.g. for "new").
+	var payload []byte
+	base := path.Base(p)
+	if len(m) == 1 {
+		if v, ok := m[base]; ok {
+			payload = []byte(fmt.Sprintf("%v", v))
+		}
+	}
+	if payload == nil {
+		payload = serializeKV(m)
+	}
 	fid, err := fsys.Open(p, plan9.OWRITE)
 	if err != nil {
 		writeJSON(w, http.StatusNotFound, map[string]string{"error": err.Error()})
 		return
 	}
-	n, err := fid.Write(serializeKV(m))
+	n, err := fid.Write(payload)
 	fid.Close()
 	if err != nil {
 		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": err.Error()})