Problem: `:CP race` on platforms without future contests (CSES, USACO)
wastes time fetching the full contest list only to discover there is
no `start_time`. The error message is also uninformative.
Solution: Add `supports_countdown` bool to `ContestListResult` (default
`True`). CSES and USACO set it to `False`. Cache the flag per-platform
so subsequent calls skip the fetch entirely. `race.lua` checks the
cached value first, then the scraper result, and shows
`"<Platform> does not support :CP race"` instead of a generic error.
## Problem
There was no way to open a problem, contest, or standings page in the
browser from within the plugin.
## Solution
Add `contest_url` and `standings_url` to `MetadataResult` and persist
them in the cache. Add `cache.get_open_urls` to resolve all three URLs.
Wire up `:CP open [problem|contest|standings]` in `commands/init.lua`
to call `vim.ui.open`, warning when a URL is unavailable (e.g. CSES
has no standings). Closes#315.
## Problem
`:CP <platform> login` blindly caches username/password without
server-side
validation. Bad credentials are only discovered at submit time, which is
confusing and wastes a browser session.
## Solution
Wire `:CP <platform> login` through the scraper pipeline so each
platform
actually authenticates before persisting credentials. On failure, the
user
sees an error and nothing is cached.
- CSES: reuses `_check_token` (fast path) and `_web_login`; returns API
token
in `LoginResult.credentials` so subsequent submits skip re-auth.
- AtCoder/Codeforces: new `_login_headless` functions open a
StealthySession,
solve Turnstile/Cloudflare, fill the login form, and validate success by
checking for the logout link. Cookies only persist on confirmed login.
- CodeChef/Kattis/USACO: return "not yet implemented" errors.
- `scraper.lua`: generalizes submit-only guards (`needs_browser` flag)
to
cover both `submit` and `login` subcommands.
- `credentials.lua`: prompts for username/password, passes cached token
for
CSES fast path, shows ndjson status notifications, only caches on
success.
Problem: problem pages contain floating-point precision requirements and
contest start timestamps that were not being extracted or stored. The
submit workflow also needed a foundation in the scraper layer.
Solution: add extract_precision() to base.py and propagate through all
scrapers into cache. Add start_time to ContestSummary and extract it
from AtCoder and Codeforces. Add SubmitResult model, abstract submit()
method, submit CLI case with get_language_id() resolution, stdin/env_extra
support in run_scraper, and a full AtCoder submit implementation; stub
the remaining platforms.
