Single shared neo-tree across diff tabs, with active-tab file highlight

[Cannon07]

Summary

When an agent proposes changes to multiple files, the plugin opens one diff per tab. Because neo-tree is tab-scoped in Neovim, switching between those diff tabs lands you in a tabpage where neo-tree is either absent or shows incomplete/stale markers. The change data is correct (the changes registry is global and the BEFORE_RENDER handler reads it), but the neo-tree window isn't consistent across tabs.

Surfaces frequently with OpenCode's multi-file / concurrent proposals.

Current behavior

• Every preview opens in a new tab — both the side-by-side renderer and the inline renderer (show_inline_diff returns a new tab).
• Neo-tree is per-tabpage, so each diff tab has its own (or no) neo-tree state.
• Switching tabs → "incomplete marked neo-tree, or no neo-tree at all."

Desired behavior

• A single neo-tree common to all diff tabs, showing all pending change markers consistently.
• Optionally, highlight/reveal the file corresponding to the currently-focused diff tab as you switch tabs.

Possible approaches (design discussion)

1. TabEnter autocmd that ensures neo-tree is present + refreshed and reveals the active tab's file.
2. Don't open a new tab per file — reuse a single diff tab, or use vsplit/inline-in-current-tab — so there's one stable neo-tree.
3. A global/shared neo-tree source rather than the per-tab filesystem source.

This touches the core "one preview = one tab" model and the reveal logic, so it needs design rather than a drop-in fix.

Notes

• Related bug (independent): Bash post-tool clears neo-tree markers globally, wiping concurrent Bash command markers #83 (Bash post-tool clears markers globally).
• Not Windows-specific.