collabd design notes

two possible sync modes
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1. text-crdt mode (current implementation)

   uses yjs for proper text crdt operations. handles insertions, deletions,
   concurrent edits with automatic conflict resolution. supports all the
   stuff editors expect: select, cut, paste, undo per user.

   pros:
   - real editor behavior
   - proper undo/redo
   - handles complex concurrent edits

   cons:
   - more complex
   - yjs overhead
   - adapters need to translate buffer ops to crdt ops

2. cell-grid mode (simpler alternative)

   treat document as 2d grid of cells at (row, col). each cell is one
   character. last write wins (or use timestamps per cell).

   basically: shared terminal buffer.

   pros:
   - dead simple
   - no crdt library needed
   - works great for terminal-native use cases
   - less adapter complexity

   cons:
   - no cut/paste (moving cells is weird)
   - no semantic operations (select word, delete line)
   - undo is per-cell, not per-action
   - inserting char doesnt shift rest of line

   good for: shared scratch buffer, terminal notepad, mob viewing
   bad for: actual code editing

could support both modes and let adapters pick. text-crdt for real editors,
cell-grid for simpler/terminal-only tools.

jquast suggested this approach - worth keeping in mind for mvp simplicity.