fix(scrapers): bad credentials detection and error message cleanup (#367)

## Problem

Wrong credentials produced garbled error messages (`"login failed: Login
failed: bad_credentials"`) and stale credentials remained cached after
failure, causing silent re-use on the next invocation.

## Solution

Standardize all scrapers to emit `"bad_credentials"` as a plain error
code, mapped to a human-readable string via `LOGIN_ERRORS` in
`constants.lua`. Fix `credentials.lua` to clear cached credentials on
failure in both the fresh-prompt and re-prompt paths. For AtCoder and
Codeforces, replace `wait_for_url` with `wait_for_function` to detect
the login error element immediately rather than sitting the full 10s
navigation timeout. Add "Remember me" checkbox on Codeforces login.

scrapers/atcoder.py

@@ -400,9 +400,13 @@ def _at_login_action(credentials: dict[str, str]):
             page.fill('input[name="username"]', credentials.get("username", ""))
             page.fill('input[name="password"]', credentials.get("password", ""))
             page.click("#submit")
-            page.wait_for_url(
-                lambda url: "/login" not in url, timeout=BROWSER_NAV_TIMEOUT
+            page.wait_for_function(
+                "() => !window.location.href.includes('/login') || !!document.querySelector('.alert-danger')",
+                timeout=BROWSER_NAV_TIMEOUT,
             )
+            if "/login" in page.url:
+                login_error = "bad_credentials"
+                return
         except Exception as e:
             login_error = str(e)
 
@@ -460,7 +464,9 @@ def _login_headless(credentials: dict[str, str]) -> LoginResult:
                 solve_cloudflare=True,
             )
             login_error = get_error()
-            if login_error:
+            if login_error == "bad_credentials":
+                return LoginResult(success=False, error="bad_credentials")
+            elif login_error:
                 return LoginResult(success=False, error=f"Login failed: {login_error}")
 
             logged_in = False
@@ -473,9 +479,7 @@ def _login_headless(credentials: dict[str, str]) -> LoginResult:
                 f"{BASE_URL}/home", page_action=verify_action, network_idle=True
             )
             if not logged_in:
-                return LoginResult(
-                    success=False, error="Login failed (bad credentials?)"
-                )
+                return LoginResult(success=False, error="bad_credentials")
 
             try:
                 browser_cookies = session.context.cookies()
@@ -570,7 +574,9 @@ def _submit_headless(
                     solve_cloudflare=True,
                 )
                 login_error = get_login_error()
-                if login_error:
+                if login_error == "bad_credentials":
+                    return SubmitResult(success=False, error="bad_credentials")
+                elif login_error:
                     return SubmitResult(
                         success=False, error=f"Login failed: {login_error}"
                     )

scrapers/codechef.py

@@ -15,7 +15,7 @@ from .base import (
     load_platform_cookies,
     save_platform_cookies,
 )
-from .timeouts import BROWSER_SESSION_TIMEOUT, HTTP_TIMEOUT
+from .timeouts import BROWSER_NAV_TIMEOUT, BROWSER_SESSION_TIMEOUT, HTTP_TIMEOUT
 from .models import (
     ContestListResult,
     ContestSummary,
@@ -84,10 +84,12 @@ def _login_headless_codechef(credentials: dict[str, str]) -> LoginResult:
             page.locator('input[name="name"]').fill(credentials.get("username", ""))
             page.locator('input[name="pass"]').fill(credentials.get("password", ""))
             page.locator("input.cc-login-btn").click()
-            try:
-                page.wait_for_url(lambda url: "/login" not in url, timeout=3000)
-            except Exception:
-                login_error = "bad credentials?"
+            page.wait_for_function(
+                "() => !window.location.href.includes('/login') || !!document.querySelector('div.error')",
+                timeout=BROWSER_NAV_TIMEOUT,
+            )
+            if "/login" in page.url:
+                login_error = "bad_credentials"
                 return
         except Exception as e:
             login_error = str(e)
@@ -105,9 +107,7 @@ def _login_headless_codechef(credentials: dict[str, str]) -> LoginResult:
 
             session.fetch(f"{BASE_URL}/", page_action=check_login, network_idle=True)
             if not logged_in:
-                return LoginResult(
-                    success=False, error="Login failed (bad credentials?)"
-                )
+                return LoginResult(success=False, error="bad_credentials")
 
             try:
                 browser_cookies = session.context.cookies()
@@ -163,10 +163,12 @@ def _submit_headless_codechef(
             page.locator('input[name="name"]').fill(credentials.get("username", ""))
             page.locator('input[name="pass"]').fill(credentials.get("password", ""))
             page.locator("input.cc-login-btn").click()
-            try:
-                page.wait_for_url(lambda url: "/login" not in url, timeout=3000)
-            except Exception:
-                login_error = "bad credentials?"
+            page.wait_for_function(
+                "() => !window.location.href.includes('/login') || !!document.querySelector('div.error')",
+                timeout=BROWSER_NAV_TIMEOUT,
+            )
+            if "/login" in page.url:
+                login_error = "bad_credentials"
                 return
         except Exception as e:
             login_error = str(e)

scrapers/codeforces.py

@@ -353,10 +353,15 @@ def _cf_login_action(credentials: dict[str, str]):
             page.wait_for_selector('input[name="handleOrEmail"]', timeout=60000)
             page.fill('input[name="handleOrEmail"]', credentials.get("username", ""))
             page.fill('input[name="password"]', credentials.get("password", ""))
+            page.locator('#enterForm input[name="remember"]').check()
             page.locator('#enterForm input[type="submit"]').click()
-            page.wait_for_url(
-                lambda url: "/enter" not in url, timeout=BROWSER_NAV_TIMEOUT
+            page.wait_for_function(
+                "() => !window.location.href.includes('/enter') || !!document.querySelector('#enterForm span.error')",
+                timeout=BROWSER_NAV_TIMEOUT,
             )
+            if "/enter" in page.url:
+                login_error = "bad_credentials"
+                return
         except Exception as e:
             login_error = str(e)
 
@@ -416,7 +421,9 @@ def _login_headless_cf(credentials: dict[str, str]) -> LoginResult:
                 solve_cloudflare=True,
             )
             login_error = get_error()
-            if login_error:
+            if login_error == "bad_credentials":
+                return LoginResult(success=False, error="bad_credentials")
+            elif login_error:
                 return LoginResult(success=False, error=f"Login failed: {login_error}")
 
             logged_in = False
@@ -427,9 +434,7 @@ def _login_headless_cf(credentials: dict[str, str]) -> LoginResult:
 
             session.fetch(f"{BASE_URL}/", page_action=verify_action, network_idle=True)
             if not logged_in:
-                return LoginResult(
-                    success=False, error="Login failed (bad credentials?)"
-                )
+                return LoginResult(success=False, error="bad_credentials")
 
             try:
                 browser_cookies = session.context.cookies()
@@ -540,7 +545,9 @@ def _submit_headless(
                     solve_cloudflare=True,
                 )
                 login_error = _get_login_error()
-                if login_error:
+                if login_error == "bad_credentials":
+                    return SubmitResult(success=False, error="bad_credentials")
+                elif login_error:
                     return SubmitResult(
                         success=False, error=f"Login failed: {login_error}"
                     )

scrapers/cses.py

@@ -266,7 +266,7 @@ class CSESScraper(BaseScraper):
             print(json.dumps({"status": "logging_in"}), flush=True)
             token = await self._web_login(client, username, password)
             if not token:
-                return self._login_error("Login failed (bad credentials?)")
+                return self._login_error("bad_credentials")
 
             return LoginResult(
                 success=True,
@@ -434,7 +434,7 @@ class CSESScraper(BaseScraper):
                 print(json.dumps({"status": "logging_in"}), flush=True)
                 token = await self._web_login(client, username, password)
                 if not token:
-                    return self._submit_error("Login failed (bad credentials?)")
+                    return self._submit_error("bad_credentials")
                 print(
                     json.dumps(
                         {

scrapers/kattis.py

@@ -344,7 +344,7 @@ class KattisScraper(BaseScraper):
                 print(json.dumps({"status": "logging_in"}), flush=True)
                 ok = await _do_kattis_login(client, username, password)
                 if not ok:
-                    return self._submit_error("Login failed (bad credentials?)")
+                    return self._submit_error("bad_credentials")
                 await _save_kattis_cookies(client)
 
             print(json.dumps({"status": "submitting"}), flush=True)
@@ -381,7 +381,7 @@ class KattisScraper(BaseScraper):
                 print(json.dumps({"status": "logging_in"}), flush=True)
                 ok = await _do_kattis_login(client, username, password)
                 if not ok:
-                    return self._submit_error("Login failed (bad credentials?)")
+                    return self._submit_error("bad_credentials")
                 await _save_kattis_cookies(client)
                 try:
                     r = await _do_submit()
@@ -421,7 +421,7 @@ class KattisScraper(BaseScraper):
             print(json.dumps({"status": "logging_in"}), flush=True)
             ok = await _do_kattis_login(client, username, password)
             if not ok:
-                return self._login_error("Login failed (bad credentials?)")
+                return self._login_error("bad_credentials")
             await _save_kattis_cookies(client)
         return LoginResult(
             success=True,

scrapers/usaco.py

@@ -439,7 +439,7 @@ class USACOScraper(BaseScraper):
                     except Exception as e:
                         return self._submit_error(f"Login failed: {e}")
                     if not ok:
-                        return self._submit_error("Login failed (bad credentials?)")
+                        return self._submit_error("bad_credentials")
                     await _save_usaco_cookies(client)
             else:
                 print(json.dumps({"status": "logging_in"}), flush=True)
@@ -448,7 +448,7 @@ class USACOScraper(BaseScraper):
                 except Exception as e:
                     return self._submit_error(f"Login failed: {e}")
                 if not ok:
-                    return self._submit_error("Login failed (bad credentials?)")
+                    return self._submit_error("bad_credentials")
                 await _save_usaco_cookies(client)
 
             result = await self._do_submit(client, problem_id, language_id, source)
@@ -463,7 +463,7 @@ class USACOScraper(BaseScraper):
             except Exception as e:
                 return self._submit_error(f"Login failed: {e}")
             if not ok:
-                return self._submit_error("Login failed (bad credentials?)")
+                return self._submit_error("bad_credentials")
             await _save_usaco_cookies(client)
 
             return await self._do_submit(client, problem_id, language_id, source)
@@ -543,7 +543,7 @@ class USACOScraper(BaseScraper):
                 return self._login_error(f"Login request failed: {e}")
 
             if not ok:
-                return self._login_error("Login failed (bad credentials?)")
+                return self._login_error("bad_credentials")
 
             await _save_usaco_cookies(client)
         return LoginResult(