Fix GitHub sync details blank state

[alvarosanchez]

Summary

• Prefer slot-provided issue context for the GitHub Sync task detail surface before falling back to useHostContext().
• Replace the post-loading blank panel with an explicit GitHub sync details troubleshooting state when issue context cannot be resolved.
• Add regression coverage and update README/SPEC guidance for the issue detail behavior.

Validation

• pnpm exec tsx --test --test-name-pattern "resolveGitHubIssue" tests/plugin.spec.ts
• pnpm typecheck
• pnpm test
• pnpm build
• pnpm test:e2e against disposable Paperclip 2026.517.0

Model Used

• Model ID/version: GPT-5 Codex via OpenAI Codex Desktop. Exact backend revision is not exposed to the agent runtime.
• Context window size: not exposed to the agent runtime.
• Capabilities: code reasoning, shell and GitHub CLI tool use, local build/test/e2e verification.

[Copilot]

Pull request overview

Improves the GitHub Sync issue detail tab experience by preferring slot-provided issue context over useHostContext(), and by replacing the “blank panel” failure mode with an explicit troubleshooting/unresolved state when issue context cannot be resolved.

Changes:

• Prefer slot context for task/detail tab issue context resolution, with host context as fallback.
• Introduce an explicit unresolved detail-tab state and render a troubleshooting panel instead of returning null.
• Add regression tests and update README/SPEC guidance for issue detail behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/ui/index.tsx	Adds slot-context resolution, introduces unresolved state, and renders troubleshooting UI for missing/unresolvable issue context.
tests/plugin.spec.ts	Adds regression coverage for unresolved state and slot-context preference logic.
SPEC.md	Updates specification language for issue detail context precedence and unresolved behavior.
README.md	Updates documentation to mention troubleshooting details when issue context can’t be resolved.

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