docs: document :CP open command in vimdoc

Problem: There was no way to open a problem or contest page in the
browser from within the plugin; users had to manually navigate to
the platform URL.

Solution: Add `contest_url` and `standings_url` to `MetadataResult`
and persist them via `cache.set_contest_data`. Add `cache.get_open_urls`
to assemble all three URLs from cache. Wire up `:CP open` in
`commands/init.lua` to call `vim.ui.open` on the resolved URL,
warning when none is available (e.g. CSES standings).

doc/cp.nvim.txt

@@ -24,15 +24,16 @@ CONTENTS                                                        *cp-contents*
  16. Race .......................................................... |cp-race|
  17. Credentials ............................................ |cp-credentials|
  18. Submit ...................................................... |cp-submit|
- 19. ANSI Colors ................................................... |cp-ansi|
- 20. Highlight Groups ........................................ |cp-highlights|
- 21. Terminal Colors .................................... |cp-terminal-colors|
- 22. Highlight Customization .......................... |cp-highlight-custom|
- 23. Helpers .................................................... |cp-helpers|
- 24. Statusline Integration .................................. |cp-statusline|
- 25. Panel Keymaps .......................................... |cp-panel-keys|
- 26. File Structure ................................................ |cp-files|
- 27. Health Check ................................................ |cp-health|
+ 19. Open ......................................................... |cp-open|
+ 20. ANSI Colors ................................................... |cp-ansi|
+ 21. Highlight Groups ........................................ |cp-highlights|
+ 22. Terminal Colors .................................... |cp-terminal-colors|
+ 23. Highlight Customization .......................... |cp-highlight-custom|
+ 24. Helpers .................................................... |cp-helpers|
+ 25. Statusline Integration .................................. |cp-statusline|
+ 26. Panel Keymaps .......................................... |cp-panel-keys|
+ 27. File Structure ................................................ |cp-files|
+ 28. Health Check ................................................ |cp-health|
 
 ==============================================================================
 INTRODUCTION                                                         *cp.nvim*
@@ -487,6 +488,17 @@ COMMANDS                                                         *cp-commands*
                                 credentials are saved.
                                 --lang: Submit solution for a specific language.
 
+            :CP open [problem|contest|standings]
+                                Open the URL for the current problem, contest,
+                                or standings page in the browser via
+                                |vim.ui.open|. Defaults to "problem" if no
+                                argument is given. Warns if the URL is not
+                                available (e.g. CSES has no standings).
+                                Examples: >
+                                    :CP open
+                                    :CP open contest
+                                    :CP open standings
+<
         State Restoration ~
             :CP                 Restore state from current file.
                                 Automatically detects platform, contest, problem,
@@ -580,6 +592,9 @@ through the same code path as |:CP|.
                                                            *<Plug>(cp-submit)*
 <Plug>(cp-submit)       Submit current solution. Equivalent to :CP submit.
 
+                                                             *<Plug>(cp-open)*
+<Plug>(cp-open)         Open current problem URL in browser. Equivalent to :CP open.
+
                                                         *<Plug>(cp-race-stop)*
 <Plug>(cp-race-stop)    Cancel active race countdown. Equivalent to :CP race stop.
 
@@ -1021,6 +1036,22 @@ Submit the current solution to the online judge.
             AtCoder     Fully implemented.
             Others      Not yet implemented.
 
+==============================================================================
+OPEN                                                                 *cp-open*
+
+Open a platform URL for the current contest in the browser.
+
+:CP open [problem|contest|standings]
+        Open the URL for the active problem, contest page, or standings.
+        Defaults to "problem" if no argument is given. Uses |vim.ui.open|.
+        Warns if the URL is unavailable (e.g. CSES has no standings page).
+
+        Platform support:
+            AtCoder     problem, contest, standings
+            Codeforces  problem, contest, standings
+            CSES        problem, contest (no standings)
+            Others      Not yet implemented.
+
 ==============================================================================
 ANSI COLORS AND HIGHLIGHTING                                         *cp-ansi*
 

lua/cp/cache.lua

@@ -10,6 +10,8 @@
 ---@field name string
 ---@field display_name string
 ---@field url string
+---@field contest_url string
+---@field standings_url string
 
 ---@class ContestSummary
 ---@field display_name string
@@ -148,12 +150,16 @@ end
 ---@param contest_id string
 ---@param problems Problem[]
 ---@param url string
-function M.set_contest_data(platform, contest_id, problems, url)
+---@param contest_url string
+---@param standings_url string
+function M.set_contest_data(platform, contest_id, problems, url, contest_url, standings_url)
   vim.validate({
     platform = { platform, 'string' },
     contest_id = { contest_id, 'string' },
     problems = { problems, 'table' },
     url = { url, 'string' },
+    contest_url = { contest_url, 'string' },
+    standings_url = { standings_url, 'string' },
   })
 
   cache_data[platform] = cache_data[platform] or {}
@@ -165,6 +171,8 @@ function M.set_contest_data(platform, contest_id, problems, url)
     problems = problems,
     index_map = {},
     url = url,
+    contest_url = contest_url,
+    standings_url = standings_url,
   }
   for i, p in ipairs(out.problems) do
     out.index_map[p.id] = i
@@ -174,6 +182,25 @@ function M.set_contest_data(platform, contest_id, problems, url)
   M.save()
 end
 
+---@param platform string?
+---@param contest_id string?
+---@param problem_id string?
+---@return { problem: string|nil, contest: string|nil, standings: string|nil }|nil
+function M.get_open_urls(platform, contest_id, problem_id)
+  if not platform or not contest_id then
+    return nil
+  end
+  if not cache_data[platform] or not cache_data[platform][contest_id] then
+    return nil
+  end
+  local cd = cache_data[platform][contest_id]
+  return {
+    problem = cd.url ~= '' and problem_id and string.format(cd.url, problem_id) or nil,
+    contest = cd.contest_url ~= '' and cd.contest_url or nil,
+    standings = cd.standings_url ~= '' and cd.standings_url or nil,
+  }
+end
+
 ---@param platform string
 ---@param contest_id string
 function M.clear_contest_data(platform, contest_id)

lua/cp/commands/init.lua

@@ -245,6 +245,12 @@ local function parse_command(args)
         debug = debug,
         mode = mode,
       }
+    elseif first == 'open' then
+      local target = args[2] or 'problem'
+      if not vim.tbl_contains({ 'problem', 'contest', 'standings' }, target) then
+        return { type = 'error', message = 'Usage: :CP open [problem|contest|standings]' }
+      end
+      return { type = 'action', action = 'open', requires_context = true, subcommand = target }
     elseif first == 'pick' then
       local language = nil
       if #args >= 3 and args[2] == '--lang' then
@@ -375,6 +381,20 @@ function M.handle_command(opts)
       require('cp.race').start(cmd.platform, cmd.contest, cmd.language)
     elseif cmd.action == 'race_stop' then
       require('cp.race').stop()
+    elseif cmd.action == 'open' then
+      local cache = require('cp.cache')
+      cache.load()
+      local urls =
+        cache.get_open_urls(state.get_platform(), state.get_contest_id(), state.get_problem_id())
+      local url = urls and urls[cmd.subcommand]
+      if not url or url == '' then
+        logger.log(
+          ("No URL available for '%s'"):format(cmd.subcommand),
+          { level = vim.log.levels.WARN }
+        )
+        return
+      end
+      vim.ui.open(url)
     elseif cmd.action == 'login' then
       require('cp.credentials').login(cmd.platform)
     elseif cmd.action == 'logout' then

lua/cp/constants.lua

@@ -13,6 +13,7 @@ M.ACTIONS = {
   'race',
   'stress',
   'submit',
+  'open',
 }
 
 M.PLATFORM_DISPLAY_NAMES = {

lua/cp/setup.lua

@@ -243,7 +243,14 @@ function M.setup_contest(platform, contest_id, problem_id, language)
       contest_id,
       vim.schedule_wrap(function(result)
         local problems = result.problems or {}
-        cache.set_contest_data(platform, contest_id, problems, result.url)
+        cache.set_contest_data(
+          platform,
+          contest_id,
+          problems,
+          result.url,
+          result.contest_url or '',
+          result.standings_url or ''
+        )
         local prov = state.get_provisional()
         if not prov or prov.platform ~= platform or prov.contest_id ~= contest_id then
           return

scrapers/atcoder.py

@@ -606,6 +606,8 @@ class AtcoderScraper(BaseScraper):
                 contest_id=contest_id,
                 problems=problems,
                 url=f"https://atcoder.jp/contests/{contest_id}/tasks/{contest_id}_%s",
+                contest_url=f"https://atcoder.jp/contests/{contest_id}",
+                standings_url=f"https://atcoder.jp/contests/{contest_id}/standings",
             )
         except Exception as e:
             return self._metadata_error(str(e))

scrapers/codeforces.py

@@ -223,6 +223,8 @@ class CodeforcesScraper(BaseScraper):
                 contest_id=contest_id,
                 problems=problems,
                 url=f"https://codeforces.com/contest/{contest_id}/problem/%s",
+                contest_url=f"https://codeforces.com/contest/{contest_id}",
+                standings_url=f"https://codeforces.com/contest/{contest_id}/standings",
             )
         except Exception as e:
             return self._metadata_error(str(e))
@@ -401,7 +403,8 @@ def _login_headless_cf(credentials: dict[str, str]) -> LoginResult:
 
             try:
                 browser_cookies = session.context.cookies()
-                cookie_cache.write_text(json.dumps(browser_cookies))
+                if any(c.get("name") == "X-User-Handle" for c in browser_cookies):
+                    cookie_cache.write_text(json.dumps(browser_cookies))
             except Exception:
                 pass
 
@@ -478,10 +481,7 @@ def _submit_headless(
         if "/enter" in page.url or "/login" in page.url:
             needs_relogin = True
             return
-        try:
-            _solve_turnstile(page)
-        except Exception:
-            pass
+        _solve_turnstile(page)
         try:
             page.select_option(
                 'select[name="submittedProblemIndex"]',
@@ -550,7 +550,7 @@ def _submit_headless(
 
             try:
                 browser_cookies = session.context.cookies()
-                if browser_cookies:
+                if any(c.get("name") == "X-User-Handle" for c in browser_cookies):
                     cookie_cache.write_text(json.dumps(browser_cookies))
             except Exception:
                 pass

scrapers/cses.py

@@ -218,6 +218,8 @@ class CSESScraper(BaseScraper):
             contest_id=contest_id,
             problems=problems,
             url="https://cses.fi/problemset/task/%s",
+            contest_url="https://cses.fi/problemset",
+            standings_url="",
         )
 
     async def scrape_contest_list(self) -> ContestListResult:
@@ -352,8 +354,12 @@ class CSESScraper(BaseScraper):
             f"{API_URL}/login", headers=HEADERS, timeout=HTTP_TIMEOUT
         )
         api_data = api_resp.json()
-        token: str = api_data["X-Auth-Token"]
-        auth_url: str = api_data["authentication_url"]
+        token: str | None = api_data.get("X-Auth-Token")
+        auth_url: str | None = api_data.get("authentication_url")
+        if not token:
+            raise RuntimeError("CSES API login response missing 'X-Auth-Token'")
+        if not auth_url:
+            raise RuntimeError("CSES API login response missing 'authentication_url'")
 
         auth_page = await client.get(auth_url, headers=HEADERS, timeout=HTTP_TIMEOUT)
         auth_csrf = re.search(r'name="csrf_token" value="([^"]+)"', auth_page.text)
@@ -388,8 +394,8 @@ class CSESScraper(BaseScraper):
                 timeout=HTTP_TIMEOUT,
             )
             return r.status_code == 200
-        except Exception:
-            return False
+        except (httpx.ConnectError, httpx.TimeoutException, httpx.NetworkError):
+            raise
 
     async def submit(
         self,

scrapers/models.py

@@ -42,6 +42,8 @@ class MetadataResult(ScrapingResult):
     contest_id: str = ""
     problems: list[ProblemSummary] = Field(default_factory=list)
     url: str
+    contest_url: str = ""
+    standings_url: str = ""
 
     model_config = ConfigDict(extra="forbid")