Fix duplicate submissions and EditArea null pointer error

[Copilot]

Users reported duplicate submissions and a JavaScript error: Cannot read properties of null (reading 'parentNode') from edit_area_full.js.

Changes

Duplicate submission prevention

• Add PassCheck.disabled = true when submission starts, reset on completion/error
• Guard checks both isPassCheckRunning flag and disabled property: if (isPassCheckRunning || PassCheck.disabled)
• Defense-in-depth: flag prevents programmatic race conditions, disabled prevents UI clicks and provides visual feedback

EditArea conflict resolution

• Delete EditArea instance before replacing submitpage.php innerHTML
• XMOJ site loads EditArea editor; userscript's HTML replacement orphans its DOM references
• Safe to fail: wrapped in try-catch since instance may not exist

Debug instrumentation

• Log submission flow when DebugMode enabled for future troubleshooting

// Before: single flag guard
if (isPassCheckRunning) return;

// After: dual guard + button state
if (isPassCheckRunning || PassCheck.disabled) return;
isPassCheckRunning = true;
PassCheck.disabled = true;  // Prevent UI clicks, show visual state

// Prevent EditArea accessing orphaned DOM nodes
if (typeof editAreaLoader !== 'undefined') {
    editAreaLoader.delete_instance('source');
}
document.querySelector("...").innerHTML = ...;  // Now safe

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Summary by cubic

Prevents duplicate submissions and double-running of PassCheck on submitpage.php, and fixes the EditArea teardown error when the page HTML is replaced. Improves error messages and makes button/state recovery reliable on network, timeout, or parse failures.

• Bug Fixes
  • Guard PassCheck/Submit with isSubmitting and isPassCheckRunning; declare flags before handlers; also check and set PassCheck.disabled during runs.
  • Better error handling: RequestAPI onerror/ontimeout with user-friendly messages; safe JSON-parse fallback; catch submission/network errors; proceed if compile-check parse fails; reset Submit/PassCheck and flags in all paths; add DebugMode logs for click/request flow.
  • Delete EditArea instance before replacing HTML (try/catch) to avoid the parentNode null error.

^{Written for commit 808dce1. Summary will update on new commits.}