Linear integration (link tickets/projects to threads) and a Collaboration tab

[Yagomfh]

Problem

Threads can link pull requests, but work is often tracked in Linear. Today there's no way to connect a thread to its Linear issue or project, so context (status, assignee, discussion) lives in another app, and the PR review conversation and the ticket conversation can't be followed in one place.

Proposal

Two changes, proposed as two separate PRs, the second stacked on the first.

1. Linear links

• Connect Linear with a personal API key (Settings → Integrations → Linear; key kept in the server secret store, LINEAR_API_KEY also read).
• Link issues and projects to a thread by URL (UI, command palette, or an agent); a thread can link several.
• A Linear right-panel tab shows linked items: status, assignee, priority, labels, sub-issues, project progress. Status/priority/assignee/lead are editable.
• Adds thread.linear.link / thread.linear.unlink orchestration commands, a threadLinearLinks environment capability (so older servers degrade cleanly), and linear.* RPCs gated by the existing settings/source-control scopes.
• Docs: docs/user/linear.md.

2. Collaboration tab (depends on 1)

• A chat-style right-panel tab merging the thread's PR comments and Linear comments into one feed, with a composer that posts to either.
• Linear replies/deletes; PR comment deletion (new pullRequests.deleteComment RPC, GitHub only; other hosts report it unsupported).

Scope and non-goals

• Opt-in: nothing changes unless a user connects Linear; the tabs are hidden when unsupported.
• Linear only, no other trackers. Only the first linked issue/project appears in Collaboration; latest 50 comments per item.
• No changes to existing PR behavior beyond the added delete-comment RPC.

Status

Both pieces are implemented and typecheck clean on a fork-ready branch stack (~3.9k lines for 1, ~0.4k for 2, mostly new files). Happy to split further, shrink scope (e.g. read-only Linear first, drop comment deletion), or hold the code until direction is agreed.

Questions for maintainers

1. Is a Linear integration in scope for T3 Code at all?
2. If so, is the split above right, or would you prefer read-only first?
3. Any objection to a personal-API-key connection (vs. OAuth)?

[juliusmarminge]

Note

Grok responding on behalf of Julius.

Thanks for the detailed write-up and for asking before opening the PRs. This overlaps #11785, which already proposes linking threads to issues (Linear included) with a linked-work panel, and its comments ask for reading and replying to issue comments inside the thread, which is your Collaboration tab. Linear as a tracker is also in progress in #19274 (personal API key in the server secret store), so a second Linear client would conflict with it.

Closing this as a duplicate so the conversation stays in one place. Please add the parts that aren't covered there (project links, the merged PR plus Linear comment feed, and PR comment deletion) to #11785, and hold the branch stack until direction is settled there.