Add the reusable browser shell primitives Phase B views build on:
- store.js: observable store (get/set/subscribe)
- events.js: job activity adapter — SSE preferred, polling fallback,
sharing the event `seq` as cursor so a transport switch drops nothing
- api.js: cancellable() (AbortController) + job endpoints; aborted
requests reject with code "cancelled"
Make the SSE stream generically consumable: emit default `message`
events with the type in the JSON payload instead of `event: <type>`, so
a browser EventSource receives the open-ended type set (state:*,
claimed, …) via onmessage without enumerating it. The `event: done`
sentinel and resumable `id:` cursors are unchanged.
Tests: frontend/js/tests/ in-browser unit suite (api errors +
cancellation, store transitions, routing, SSE→polling fallback) served
over the app's static mount and driven by tests/e2e/test_frontend_shell.py,
which also asserts asset loading, deep-link + reload restore, JSON-only
/api/v1, and a clean console/network. Reuses the installed playwright —
no JS toolchain added.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
