fix(browser-tabs): gate tabs on contexts opt-in

[pauldambra]

Summary

• mount the browser tab strip only when Contexts is enabled
• restore new-tab behavior on cloud runs for opted-in users
• keep tab shortcuts and route synchronization inactive for users who have not opted in

Testing

• git diff --check
• Typecheck not run locally because Node.js and pnpm are unavailable in this worktree environment

Follow-up to #3385.

---

Created with PostHog Code

[trunk-io]

Merging to main in this repository is managed by Trunk.

• To merge this pull request, check the box to the left or comment /trunk merge below.

After your PR is submitted to the merge queue, this comment will be automatically updated with its status. If the PR fails, failure details will also be posted here

[github-actions]

React Doctor found 1 issue in 1 file · 1 warning.

1 warning

src/router/routes/__root.tsx

• ⚠️ src/router/routes/__root.tsx:293 Event logic handled in an effect no-event-handler

_{Reviewed by React Doctor for commit e571e20.}

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 2aaa1474bb

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[stamphog]

The bot reviewer identified a real unresolved bug: showBlankTab at line 307 of __root.tsx is still computed and rendered unconditionally (not gated on channelsEnabled), so users who disable Contexts while a blank tab is open at /website will see a dead BlankTabView with no way to navigate out, even though the strip itself is unmounted.

[github-actions]

The redirect now uses channelsEnabled (combining the remote flag and local toggle), so a user who disables Contexts while on /website is immediately routed away — the blank-tab concern the bots raised on an older commit is reduced to a single async render cycle, not a permanent stuck state. No crashes, data loss, or security issues found.