Mirrors the PR detail pattern for issues: GitHubClient.getIssueDetail (gh issue view --json comments, REST fallback) + closeIssue (gh issue close, REST PATCH fallback); new POST /api/github/issues/detail + /issues/close routes. The Issues preview fetches comments on selection (cached, non-blocking) and renders them below the body; a Close-issue button in the preview header (open issues only) closes via the API, toasts, and reflects the closed state without dismissing the view.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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