docs(design): strike what the sheet editing plan already shipped

[andiwand]

🤖 Generated with Claude Code

Docs only. docs/design/spreadsheet-editing.md says of itself that it is "a plan, not a record — update it as steps land", and steps 0 to 3 landed (#884 → #888) without three of its sections following.

What changed

• Low-hanging fruit: all six items are in, so twelve lines of cost framing become three naming them.
• Complications: five are marked done with what answered them — the ods repeat split and the xlsx shared strings (step 2), the row reflow, the shape anchor, and sort-with-edit. Four are still true and untouched: sheets past the cut, one log across several views, encrypted packages, and the locale.
• Spikes: 1 and 3 are answered — the first by step 3.4 (LibreOffice recomputes whatever an .ods cached), the third by step 2's run-index insert.
• Open questions: the last one is answered. odr::ErrorCode (feat!: one ErrorCode space every binding reports #883) is the one C++ table the page and every binding report a refusal from, written into the script by frontend.cpp::write_error_codes.

What is left, after this

Step 4 (the evaluator, the incremental recompute, Document::recalculate, formula input) and step 5. src/odr/internal/formula/ holds a parser, a writer, an AST and the dependency walk, and no evaluator.

https://claude.ai/code/session_01VVmjmddv2Ui17Nptc1ggue