fix(ui): prevent duplicate windows by implementing buffer-to-window binding

[sudo-tee]

This should close #144

[Copilot]

Pull request overview

This PR introduces a new buf_fix_win module that prevents buffers from appearing in multiple windows simultaneously, addressing a limitation where winfixbuf only prevents windows from changing buffers but doesn't prevent buffers from appearing in multiple windows. The implementation uses autocmds to monitor and close duplicate windows whenever a buffer appears in more than its intended window.

Changes:

• Added a new buf_fix_win module with autocmd-based window enforcement logic
• Integrated buffer-to-window binding in both input and output window creation
• Added comprehensive test coverage for the new module including edge cases and autocmd behavior
• Made minor refactoring improvements to autocmds.lua for consistency

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
lua/opencode/ui/buf_fix_win.lua	New module implementing buffer-to-window binding using autocmds to close duplicate windows
lua/opencode/ui/output_window.lua	Integrated buf_fix_win in buffer creation; added bufhidden and buflisted options
lua/opencode/ui/input_window.lua	Integrated buf_fix_win in buffer creation; added bufhidden and buflisted options
lua/opencode/ui/autocmds.lua	Refactored to use locally-required modules instead of inline requires; removed trailing blank line
tests/unit/buf_fix_win_spec.lua	Comprehensive test suite covering basic functionality, edge cases, autocmd setup behavior, and VimResized event handling

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