Implement stateful Notifications domain for @counterfact/github

[Copilot]

Summary

Implemented the Notifications domain in the GitHub simulator by replacing random responses with stateful thread/subscription behavior and wiring it through a dedicated domain context. This adds realistic global and repo-scoped notification flows (list, mark read, mark done, manage subscription).

Original Prompt

Implement the next task from .github/todo in counterfact/apis: complete .github/todo/notifications-v2.md by adding a dedicated routes/notifications/_.context.ts, wiring it into root context and test harness, implementing all notifications/thread/subscription/repo-notifications route handlers, seeding notification scenario data, adding unit and route tests, deleting the completed todo file, and creating a PR.

Manual acceptance tests

• GET /notifications returns seeded unread threads.
• PUT /notifications returns 202 and subsequent GET /notifications excludes those threads by default.
• GET /notifications/threads/:id returns thread data for existing IDs and 404 for unknown IDs.
• PATCH /notifications/threads/:id returns 205 and the thread is no longer unread.
• DELETE /notifications/threads/:id/subscription returns 204, and subsequent GET for that subscription returns 404.
• PUT /repos/:owner/:repo/notifications marks only that repo’s threads as read (other repos remain unread).

Tasks

• Notifications domain context

  • Added github/routes/notifications/_.context.ts with notification + subscription state stores and methods:
    • save/get/list notifications
    • mark thread read/done
    • mark all read (optionally scoped by owner/repo)
    • get/set/delete thread subscription
  • Implemented unread-by-default listing semantics (all=false behavior), repo scoping, pagination, and participating filter behavior.

• Root context + harness wiring

  • Added notifications delegation methods to github/routes/_.context.ts.
  • Registered /notifications in github/test-support/create-context.ts.

• Route implementations

  • Replaced random responses with context-backed behavior in:
    • routes/notifications.ts
    • routes/notifications/threads/{thread_id}.ts
    • routes/notifications/threads/{thread_id}/subscription.ts
    • routes/repos/{owner}/{repo}/notifications.ts
  • Normalized thread_id handling via String($.path.thread_id) before lookup/mutation.

• Scenario seeding

  • Added notifications scenario in github/scenarios/index.ts and included it in seedGitHub.
  • Seeded multiple unread threads for counterfact/platform-api and initial thread subscription state.

• Tests

  • Added github/test/notifications.context.test.ts for direct domain-context unit coverage.
  • Extended github/test/routes.test.ts with notification HTTP-route coverage (global, thread, subscription, repo-scoped flows).

• Example behavior

  // thread_id is normalized before lookup
  const threadId = String($.path.thread_id);
  const thread = $.context.getNotification(threadId);
  if (!thread) return $.response[404].empty();
  return $.response[200].json(thread);

• Task cleanup

  • Removed completed todo file: .github/todo/notifications-v2.md.