feat(web): open GitHub issue links beside the thread

[AVGVSTVS96]

Problem

A pull request link in a thread opens beside the conversation, but a GitHub issue link leaves the app for the browser. Agents link issues all the time, for example "this is tracked in #123" or a bug they filed, and reading one means switching windows.

Proposed in Ideas: #14909 (an issue viewer like the pull request one, starting read-only). It has no maintainer reply yet, so this is offered as a concrete version of that proposal, not as an approved feature.

What changed

Clicking a GitHub issue link in a thread opens a read-only issue tab in the right panel, next to any pull request tabs. The tab shows the title, state (open, closed, not planned, duplicate), author, assignees, labels, description, reactions, and the most recent comments.

Before: an issue link opens github.com	After: the issue opens beside the thread

Comments	A #2829 reference inside an issue still opens the PR view

How it works

The issue read follows the pull request read path, so it gets routing, credentials, rate limits, caching, and refresh without new machinery.

• Contract: new issues.detail RPC. It takes the existing PullRequestRef, since a repository numbers its issues and pull requests from one sequence, and returns IssueReadResult: either issue or pull-request with its URL. New issues environment capability, so older servers keep opening issue links on the host.
• Server: PullRequestService.issue, cached and credential-keyed like preview. Providers get an optional getIssue. GitHub implements it with one GraphQL issueOrPullRequest query (newest 100 comments, with avatars and reactions). Other providers return provider-unsupported.
• Client runtime: an issue query atom next to detail and preview, added to the pull request router's read set. pullRequests.invalidate refreshes it, so the panel's refresh button skips the server cache.
• Web: an issue right-panel surface (same id scheme as pull-request), a tab icon that shows the issue's state, and IssueDetailPanel, built from the existing PR markdown, comment, actor, label, reaction, and empty-state components. Reactions are shown read-only.

Links

• A plain github.com/{owner}/{repo}/issues/{n} link opens the issue tab straight away. If GitHub says the number is a pull request, the tab swaps itself for the pull request view.
• A #123 reference (data-pull-request-autolink="reference") already asks whether the number is a pull request first. If it isn't, it now also asks whether it is an issue and opens the tab only when it is. GitHub writes discussion references as /issues/{n} too, and those still open in the browser.
• parseChangeRequestUrl is unchanged. A separate parseIssueUrl recognizes GitHub hosts only, so mobile's work-log parsing is unaffected.

Surfaces

• Clients: web and desktop. Mobile has no in-app pull request view (it opens PR links with Linking.openURL), so issue links keep opening externally there.
• Entry points: links in thread messages, and links inside PR and issue bodies shown beside a thread. On the Pull Requests page, issue links still open in the browser because that page's shared panel only renders pull request surfaces.
• Hosts: GitHub and GitHub Enterprise. Forgejo, GitLab, Bitbucket, and Azure DevOps issue links are unchanged.
• Agents/MCP: not added. This is a read-only view of a link the agent already has, and agents read issues through gh.
• Docs: an "Issues" section in docs/user/source-control.md.

Verification

• vp test run src/pullRequest/gitHubPullRequestJson.test.ts (server): 3 new tests. A pull request behind an issue number decodes as pull-request, the state reason maps correctly and is dropped on reopened issues, and truncated comment counts and viewer reactions are right.
• vp test run src/changeRequestUrl.test.ts (shared): 2 new tests for parseIssueUrl.
• The existing PullRequestService, GitHubPullRequestProvider, RpcAuthorization, client-runtime pullRequests, and web rightPanelStore and openPullRequestLink tests pass. Typecheck is clean in contracts, server, client-runtime, shared, and web. Lint shows no new warnings in the changed files.
• Ran ISSUE_GRAPHQL_QUERY live through gh against this repo and decoded the results: [Feature]: Auto Settle, hide a running thread and settle it silently when it's done #13630 (open issue, labels, reactions), [Question] Is there a way to work with multi-repo projects? #1453 (closed, completed, 16 comments), and feat(threads): settle working threads once idle on V2 #15648 (a PR, decoded as pull-request).
• Manual pass on vp run dev with a migrate-dev-db snapshot, using the screenshots above:
  • A plain issue link opened the issue tab.
  • A #13630 issue reference inside an issue body opened a second issue tab.
  • A #2829 PR reference opened the PR view.
  • A #6945 discussion reference opened github.com, as before.

Not checked: GitHub Enterprise Server versions older than 3.5, which lack Issue.stateReason and would fail the query. The desktop Electron build was not run; it uses the same web surface.

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