Share and hand off threads from the phone: Share with guest on mobile, /handoff, and a view-only guest link

[kvnloo]

Before submitting

✅ I searched Discussions, issues and PRs. Closest: #27708 (team sessions with roles; this asks for the smaller steps underneath it), #17196 (closed as a duplicate), #11820 (export). Guest links (#24104) are what this builds on.

TL;DR

Guest links and forks already do most of what "share this chat" and "hand this chat off" need. From the Android app, though, you can't reach either: the thread's 3-dot menu has no Share with guest, and typing /handoff brings up nothing. I'd like to close that gap in three small steps:

1. Mobile parity: create a guest link from the thread's 3-dot menu (Android) and header options (iOS), with the native share sheet. Web already has this in the sidebar, the thread menu and the command palette. Mobile can only send, dismiss or stop a share that already exists.
2. /handoff [focus]: a built-in composer command on web and mobile. It runs thread.fork at latest_stable into a new thread, opens that thread, and sends the focus text as its first message. It reuses the existing context transfer (native fork, or the portable handoff when the provider changes) and adds no new contract.
3. View-only guest link: the same guest page, minus the composer. This is the "viewer" role from Share threads with multiple people for team working sessions #27708 without any of that idea's account or presence machinery.

Why

I drive T3 mostly from my phone. Two things I do in other harnesses I can't do from the phone here:

• Continue in a clean thread. When a thread gets long or drifts, I want a new one that carries the useful context and starts on a focus I name. A fork already does that; it just isn't one command. oh-my-pi has /handoff [focus], and several comments on feat(thread): export complete conversation history #11820 ask for handoff between providers.
• Bring a friend in. I want to send someone the live thread so they can follow along and suggest prompts. Guest links cover that exactly, but only from desktop/web today.

Proposed behavior

Entry point	Web	Android	iOS
Share with guest	already there	3-dot menu → share sheet / copy	header options → share sheet / copy
/handoff [focus]	composer popup	composer popup	composer popup
Hand off to new thread	(fork from a response already exists)	3-dot menu	header options

• /handoff is disabled with the existing fork reasons: before the first completed reply, and while a turn runs.
• If a provider also exposes a /handoff command, T3's built-in is listed first and the provider's stays reachable.
• The guest link errors (disabled → turn on Settings → Labs → Guest links; connect_unavailable) show as they do on web.

Questions for maintainers

1. Is a /handoff built-in welcome? Or should it stay a fork entry in the menus, with no slash command?
2. Would you take mobile Share with guest as a parity fix PR without a separate approval?
3. Is a view-only guest link a reasonable first step toward Share threads with multiple people for team working sessions #27708, or would you rather design the roles together?

Prior art

• oh-my-pi: /collab (control) and /collab view (read-only) live sharing; /share (redacted snapshot); /handoff [focus].
• A downstream prototype of steps 1–2 is in progress on my fork (RFC: RFC: share a chat — /handoff to a new thread and collab guest links, Android first kvnloo/t3code#72). I'll add the Android before/after recording here once it runs on a real device.

Written with Claude Opus 5.5 (Hermes ACP in T3 Code); reviewed and posted by me.