Cite cannot send a quote to a side chat; it always goes to the main thread #31782

What happened

In the desktop app I select text in an assistant reply and click Cite, then send. The agent answers in the main chat. I want to ask about the quoted text in a side chat. Today the only way is to copy the text, type /btw, paste it, and send. Cite should be able to send to a side chat directly.

Diagnosis

Cite and side chat don't work together:

• Cite inserts a serialized t3-citation link at the cursor (apps/web/src/components/chat/ChatComposer.tsx, citeAssistantText). The selection toolbar has a single action, "Cite selection in composer" (AssistantSelectionToolbar.tsx). It has no side-chat target.
• Side chat routing only happens when the prompt text starts with the command: parseSideChatCommand matches ^/(?:side|btw) (packages/shared/src/composerTrigger.ts). A prompt that starts with a citation never matches, so it is sent to the main thread.
• The /side and /btw slash menu items are hidden unless the caret is at the start of the prompt (composerSlashCommandSearch.ts, slashCommandItemsForPromptPosition). So once a citation is in the composer, the menu doesn't offer /btw.

Possible approaches (either works for the reporter):

• Add a "Side chat" action next to Cite in the selection toolbar that starts a side chat seeded with the citation.
• Let /btw be added in front of an existing citation, and route that message to the side chat.

Whichever is chosen, the side-chat path should expand citations the same way the main send does (see #16327), not forward the raw link.

Steps to reproduce

1. In the desktop app, open a thread that has an assistant reply.
2. Select text in the reply and click Cite.
3. Type a question and send.
4. The reply appears in the main thread, and there is no way to send the quote to a side chat.
5. Workaround: copy the text, type /btw , paste, and send. That opens a side chat.

Version

0.1.8-nightly.20261106.4247 (desktop app)

Environment

Windows 11 Pro 10.0.26300 x64, Node v24.22.1

Evidence

No logs needed; this is UI behavior. The source references are listed under Diagnosis (tag v0.1.8-nightly.20261106.4247).

Related issues

#25533 asked for an Aside action next to Cite using /btw; closed as completed with no linked PR, and this build has no such action (probably superseded by the general side chat in #26454, which left selected text out). #16327: citations reach providers as raw links. #29976: /side from the slash menu should open the side chat right away.

Fix applied or workaround

Nothing was changed on the machine. Workaround: copy the text, type /btw, paste, and send.

Filed by

Claude Code (claude-opus-5-5) via t3 triage