gridcraft/CLAUDE.md

GridCraft — instructions for agents

GridCraft is a clean-room, open-source, Rust-native spreadsheet targeting Microsoft Excel parity — and superiority (speed, openness, agent control). It runs natively on macOS, Windows, Linux and BSD, and on the web via WASM. Siblings with the same conventions: ../designcraft (InDesign-class, the closest reference), ../photocraft (Photoshop), ../vectorcraft (Illustrator), ../pdfcraft (Acrobat), ../filmcraft (Premiere), ../lightcraft (Lightroom), ../effectcraft (After Effects).

Standards and learnings shared across the crafting apps live in ../../craftrules (checked out next to the craft apps, or storytold/craftrules). Read its AGENTS.md at the start of a session, follow its standards, and contribute reusable learnings back there. Never code: repos don't share code.

Start every session here

1. Read plan/STATUS.md (current milestone, next task), then the task in plan/execution-plan.md and the relevant plan/architecture.md section. Behaviour reference: plan/excel/*.md (observed-ui.md holds measured observations of the running app).
2. Follow the autonomous operation protocol (plan/execution-plan.md §7). Don't stop to ask unless §7 lists the decision as the user's.

plan/ is gitignored (local only).

Assets and iconography — absolute rule

No Microsoft, Adobe, Avid, Autodesk (or any other vendor's) iconography, images, artwork, fonts, templates, themes or sample files — ever. This is the most important rule in this repository; breaking it is a serious failure.

• Every asset in the repo is original work by GridCraft contributors, or public domain / CC0, or open source / Creative Commons that allows redistribution (or licensed open source by the contributor who created it).
• Every asset file has a row in ATTRIBUTION.md (author, source, licence). cargo xtask assets enforces it. Adding an asset without a row is a bug.
• Prefer art generated in code: the UI icon set (crates/ui-egui/src/icons.rs), table and cell style palettes, themes and sample workbooks are drawn/defined in code and original.
• Never copy Office's icons, ribbon artwork, theme XML, table-style definitions, templates, clip art or wording beyond feature names. Excel feature names (menu labels, function names) are fine.
• Screenshots of Microsoft software are never committed (they live only in plan/excel/screenshots/).
• The ArtCraft brand files in docs/brand/ are ArtCraft trademarks under docs/brand/LICENSE-brand.txt, the one exception.

Never crash

People trust GridCraft with their numbers; a crash loses their work. This outranks feature work. Standard: craftrules/standards/never-crash.md.

• No panics in non-test code: no unwrap(), expect(), panic!, unreachable!, todo!, unimplemented!; no unsafe (unsafe_code = "forbid").
• Errors are Result<T, E> through the crate's error type and ?.
• Input-derived numbers are hostile (files, formulas, commands, MCP/control params): get() instead of indexing, checked/saturating arithmetic, cap input-sized allocations (huge ranges, REPT, SEQUENCE, whole-column references).
• Bound recursion (formula nesting, dependency chains, names referring to names).
• Last-resort guard: Session::execute catches escaped panics and restores the workbook. It's a safety net, not a licence.
• Prove it: every crash fix lands with a regression test (tests::every_command_survives_empty_params fuzzes every command; crates/engine/tests/command_sequence_fuzz.rs fuzzes random command sequences against undo/redo, XLSX round-trip and full-recalc invariants; soak it with GRIDCRAFT_FUZZ_SEEDS/GRIDCRAFT_FUZZ_STEPS, replay with GRIDCRAFT_FUZZ_SEED).
• Crates carry #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)].

Non-negotiables

• Clean-room. Microsoft Excel is installed on the dev machine and may be observed black-box: run it, use its UI with synthetic workbooks, take screenshots (by window id) stored only under plan/excel/screenshots/. Never read, disassemble or copy anything inside the Office bundle, never commit files produced by Excel, never copy GPL/AGPL/LGPL code (LibreOffice, Gnumeric…). Function behaviour comes from public documentation and observation.
• Fonts live in storytold/craft-fonts, never in this repo. It is an optional build input (CRAFT_FONTS_DIR); without it the app uses system fonts and egui's defaults. Standard: craftrules standards/fonts.md.
• Test corpora (real Excel-authored files) live in a separate corpus repo, fetched pinned and sha256-verified (craftrules standards/test-corpora.md). Never commit large binary fixtures; build test workbooks in code.
• Everything is a command. User-visible behaviour = a command in crates/engine/src/cmd/* (id, label, ribbon path, shortcut, params doc, enabled, run) + tests. Ids follow Excel's ribbon (home.bold, insert.chart, data.sortAscending) plus primitives (cell.set, selection.set, range.setValues). UI-only commands live in crates/ui-egui. The control channel, CLI and MCP reach all of them.
• Programmatic calls never open dialogs: a command with empty params runs with defaults or returns an error; only menu-style invocation opens a dialog (UiRequest::Dialog).
• Layering is enforced by cargo xtask layers: core/numfmt (L0) → formula/functions (L1) → model/calc/xlsx (L2) → chart (L3) → engine (L5) → ui-egui/mcp (L6) → apps/* (L7). Nothing below L6 depends on egui/eframe/winit/rfd. The UI crate is swappable.
• The UI is thin: panels read engine state and act through app.run(id, params). Colours come from theme::Tokens.
• Rust only (no handwritten JS/TS). Never break wasm (cargo xtask wasm).
• Quality gates before every commit: cargo xtask ci (fmt, clippy -D warnings, tests, assets, layers, wasm). One task id per commit (M2.1: borders gallery).

Running and looking at the app

• cargo run --release -p gridcraft -- --sample sales --control 7979 (sample workbook + control channel).
• Drive it: JSON lines on 127.0.0.1:7979, e.g. {"id":1,"method":"engine.execute","params":{"command":"cell.set","params":{"cell":"B2","input":"=SUM(A1:A9)"}}} then {"id":2,"method":"ui.screenshot","params":{"path":"/tmp/shot.png"}}. Methods: crates/ui-egui/src/control.rs, docs: docs/control-protocol.md.
• Offscreen UI render (no window, from a source checkout): cargo run -p gridcraft-ui-egui --example snapshot -- --sample sales out.png.
• Headless: gridcraft-cli eval '=SUM(1,2,3)', gridcraft-cli run --in book.xlsx --cmd 'home.bold={"range":"A1:C1"}' --out book.xlsx, gridcraft-cli mcp.
• For UI work, look at the result (snapshot PNG) and compare with plan/excel/observed-ui.md.
• Shell gotcha: mv/cp are aliased interactive here — use /bin/mv -f / /bin/cp -f. macOS has no timeout; use perl -e 'alarm 60; exec @ARGV' cmd.
• Parallel agents: separate CARGO_TARGET_DIR per agent; edit only the crates you own; delete your target dir when done.

Roadmap

ROADMAP.md (committed) is the one-page summary: stage, headline numbers, dimensions, languages, progress log. It follows craftrules standards/progress-docs.md and points at the detail in docs/: target-app-parity.md (authoritative assessment), gaps.md (ranked work list: pick from it), roadmap.md (current focus, beta gates, milestones), architecture.md, and the area checklists function-parity.md, chart-parity.md, file-format-parity.md, ui-parity.md, hardware-parity.md, localization-parity.md. Update the affected docs (and their timestamp lines and revision history) whenever work lands. cargo xtask parity regenerates docs/parity-checklist.md from crates/engine/src/catalog.rs.