[Feature Request]: Support Editing/Deleting User Messages & In-Chat Model Switching in Web Chat & Agent Mode

Problem Statement

In chat.z.ai (both standard Chat and Agent mode):

1. Message Mutability: Users currently cannot edit or delete their previously sent messages within a conversation thread. Minor typos, formatting slips, or erroneous prompts require either branch regenerations or abandoning the chat entirely.
2. Model Hot-Swapping on Existing Chat: When an active model encounters downtime, rate limits, or when a user simply wishes to switch models mid-conversation, chat.z.ai forces/redirects users into a brand-new chat session, completely severing conversation context and history.

Proposed Solution / Feature Specification

1. User Message Edit & Delete:

   • Add inline Edit (pen icon) and Delete (trash icon) actions on user message bubbles in both standard Web Chat and Agent Mode.
   • Editing a previous turn should truncate or fork the subsequent turns cleanly and trigger a re-run from that checkpoint.
   • Deleting a turn should remove the selected message (and optionally its assistant reply) from the context window.

2. In-Chat Seamless Model Switching:

   • Allow switching the active model (e.g. from GLM-5.3 to GLM-5.3-Flash or fallback models) directly from the top model selector dropdown within the same chat thread.
   • Preserve complete preceding conversation history and context rather than redirecting to a fresh chat.

Community Context & Original Report

• Reported by: kirb on Z.ai Community Discord
• Scope: chat.z.ai (Web Chat & Agent mode)
• Feedback thread citation:

  "I think being able to delete your messages or edit them is a primal necessity, also when a model is down and you need to use another one, it should stay on the same chat instead of redirecting to a new one... talking about chat and agent mode on z.ai directly."

This request targets chat.z.ai's standard Web Chat and Agent Mode, but names no source files, tests, or implementation repository. Start by locating the message bubbles and top model selector entry points, then define behavior for editing, deleting, truncating or rerunning turns, and switching models while preserving history; done means these flows work in both modes.