Feature request: Add Selection to Conversation for chat responses (like Codex)

[cszr-liuxiaobo]

Problem

When a user selects text inside a Copilot chat response (or a previous chat message), there is currently no built-in way to add that selected text back into the current chat input as context — unlike OpenAI Codex, which shows a floating "Add to conversation" button (and a context-menu item) whenever text inside the conversation is selected.

Currently in VS Code:

• Add Selection to Chat (github.copilot.chat.attachSelection) only works for editor text / files; it does nothing when the selection is inside a chat response.
• Selecting text in a chat response only offers Copy / Copy as Markdown; there is no "Add to conversation" affordance (neither floating button nor context-menu item).
• Chat input drag-and-drop only accepts files, folders, images, URLs, symbols, problems, SCM changes, or whole-chat references — plain text selected from a chat response cannot be dropped in.
• To quote or reference part of a previous response in the same conversation, users must manually copy & paste, which is disruptive.

Solution

Add a "Add Selection to Conversation" affordance for text selected inside chat responses / messages, matching the Codex UX:

1. When the user selects text inside a chat response, show a small floating action bar (like Codex) with an action such as "Add to Conversation".
2. Also add a context-menu item ("Add Selection to Conversation") when right-clicking selected chat response text.
3. Clicking it should attach the selected text to the current chat input as a quoted/context reference (e.g. as a #-mention-style context chip or an inline quoted block), so the user can keep typing in the same conversation without copy-paste.

The existing "Ask Question" (side chat) behavior on selection can remain as a complementary option.

Alternatives considered

• "Ask Question" side chat (new Agents window): works, but spawns a separate side chat instead of adding the text to the current conversation input.
• #session mention / drag a whole chat as context: references an entire conversation, not a specific paragraph.
• Copy & paste: works, but is exactly the manual workaround this request aims to eliminate.

Additional context

• VS Code stable, latest (2026). Copilot Chat is now bundled in this repo (extensions/copilot).
• This mirrors the well-received "Add to conversation" selection UX from OpenAI Codex, which many users expect in Copilot Chat.
• No public extension API can implement this today (chat response selection is not exposed), so it needs to be a built-in feature.