## Problem
After the initial submit hardening, two issues remained: source code was
read in Lua and piped as stdin to the scraper (unnecessary roundtrip
since
the file exists on disk), and CF's `page.fill()` timed out on the hidden
`textarea[name="source"]` because CodeMirror owns the editor state.
## Solution
Pass the source file path as a CLI arg instead — AtCoder calls
`page.set_input_files(file_path)` directly, CF reads it with
`Path(file_path).read_text()`. Fix CF source injection via
`page.evaluate()`
into the CodeMirror instance. Extract `BROWSER_SUBMIT_NAV_TIMEOUT` as a
per-platform `defaultdict` (CF defaults to 2× nav timeout). Save the
buffer
with `vim.cmd.update()` before submitting.
Problem: closing the test editor left cp://test-N-* buffers alive,
causing E95 on reopen. The nofile buftype also rejected :w, which
was counterintuitive in an editable grid.
Solution: delete all test buffers in toggle_edit teardown. Switch
buftype to acwrite with a BufWriteCmd autocmd that persists test
cases and clears the modified flag. Hoist save_all_tests above
setup_keybindings so the autocmd closure can reference it.
