# GridCraft control protocol

Start the desktop app with a control port:

```sh
gridcraft --control 7979            # or GRIDCRAFT_CONTROL_PORT=7979
```

Then send newline-delimited JSON to `127.0.0.1:7979`. Every request line gets one reply line:

```json
{"id": 1, "method": "engine.execute", "params": {"command": "cell.set", "params": {"cell": "B2", "input": "=SUM(A1:A9)"}}}
{"id": 1, "ok": true, "result": {"cell": "B2", "value": "45"}}
```

Errors come back as `{"id": …, "ok": false, "error": "…"}`.

A line that is not a JSON object with a string `method` (an HTTP request, text that isn't JSON,
bytes that aren't UTF-8, a line over 64 MiB) gets one error reply and the server closes the
connection; nothing sent after it runs. Blank lines are skipped.

## Methods

| Method | Params | What it does |
|---|---|---|
| `engine.execute` | `{command, params}` | Runs any engine command (see `engine.commands` or `gridcraft-cli commands`). `edit.goTo`, `edit.goToSpecial`, `selection.set` and `selection.move` scroll the active cell into view, as Go To does in the window |
| `engine.commands` | `{search?}` | Every command: id, label, ribbon path, shortcut, params doc, enabled; `search` keeps those whose id, label or ribbon path contains it (case-insensitive) |
| `engine.journal` | | Commands run so far (replayable). Passwords (`password`, `…Password` params) are left out, so a replayed Protect Sheet has no password. Capped at 10,000 entries and 64 MB (serialized); past either cap the oldest entries go |
| `document.inspect` | | Workbook summary: sheets, used ranges, tables, charts, names, selection, undo labels |
| `sheet.read` | `{range?, sheet?, formulas?, formatted?}` | Values (or formulas / displayed text) of a range |
| `cell.get` | `{cell?}` | One cell: value, formula, displayed text, style, merge, comment, link |
| `ui.inspect` | | UI state: ribbon tab, editor, open dialog, Backstage page, message, grid rect, scroll, perf |
| `ui.click` / `ui.drag` / `ui.move` | `{x, y, toX?, toY?, button?, count?, shift?, cmd?, alt?}` | Real pointer input in window points; refused with an error if it would leave more than 10,000 pointer events queued |
| `ui.cell.click` / `ui.cell.drag` | `{cell}` / `{from, to}` | Pointer input at a cell's centre (works in point mode while editing); same 10,000-event queue limit |
| `ui.key` / `ui.text` | `{key, shift?, cmd?, alt?, ctrl?}` / `{text}` | Keyboard input (typing in the grid starts editing) |
| `ui.edit.begin` / `ui.edit.text` / `ui.edit.commit` / `ui.edit.cancel` | `{text?}` / `{move?: down\|right\|up\|left\|none}` | Drive the cell editor |
| `ui.ribbon` | `{tab}` | Switch ribbon tab |
| `ui.dialog` / `ui.dialog.set` / `ui.dialog.confirm` / `ui.dialog.cancel` | `{name}` / `{field, value}` | Open, fill in and confirm dialogs; `confirm` runs the dialog's command with the same parameters as its OK button |
| `ui.backstage` (via `engine.execute`) | `{page?: home\|new\|open\|info\|saveAs\|print\|export\|options\|account\|close}` | Open the File tab's Backstage view on a page, or close it (`ui.inspect` reports the open page as `backstage`) |
| `ui.screenshot` | `{path?}` | PNG of the window (base64 when no path). Animations are settled first: the picture shows the final state |
| `ui.set` | `{dark?, formulaBar?, ribbonCollapsed?, animations?}` | UI preferences (`formulaBar` runs `view.formulaBar`) |
| `ui.resize` / `ui.focus` | `{width, height}` | Window control |
| `app.open` / `app.save` / `app.quit` | `{path, password?}` / `{path?}` | Files and lifetime. `password` opens a password-protected workbook; without it, such a workbook returns an error (never a dialog) |

Any other method name that is a command id (e.g. `home.bold`) runs that command.

Use `engine.execute` with `{command: "view.theme", params: {mode: "system"}}`
to choose the display theme; `mode` accepts `"system"`, `"light"`, or `"dark"`.
System follows live OS appearance changes and falls back to Light when the platform supplies no preference.
The saved choice remains System; new users still start in Light. The legacy
`view.darkMode` command and `ui.set {dark}` select a fixed Light or Dark theme.

`{command: "view.animations", params: {on: false}}` turns motion in the UI off (the selection
outline then jumps to a new selection instead of gliding there); without `on` it toggles. It is
the View ▸ Animations checkbox, saved with the other UI preferences and on by default.

`{command: "app.language.set", params: {language: "ja"}}` switches the interface language
(`code` is accepted as an alias for `language`); `app.language.english` and
`app.language.japanese` are shortcuts. `engine.commands` lists every code it takes (`en`, `es`,
`zh`, `ja`, `ko`, `ru`, `pt`, `de`, `cs`, `fr`, `sr`), as does the error for an unknown one. Only
interface chrome is translated, never command ids or document text. The choice is saved in `ui.json`; with nothing saved the desktop app follows the
system language.

`{command: "file.open", params: {path: "Secret.xlsx", password: "…"}}` opens a password-protected
workbook (Agile or Standard encryption). Without `password` it returns an error containing
"is password-protected. Enter its password to open it." and never opens a dialog; a wrong
password returns "The password is incorrect." The password is left out of the journal and never
quoted in an error. The opened workbook has no save path, so Save asks where to save it, without
the password, and never replaces the encrypted original.

For a headless equivalent (no window), use `gridcraft-cli mcp` or `gridcraft-cli run`;
see [`mcp.md`](mcp.md) and [`cli.md`](cli.md).

### Native printing

Desktop `engine.commands {"search":"print"}` (and connected MCP `list_commands`)
lists `ui.printSettings` and `ui.printSubmit` with their parameter and result fields.

`engine.execute` can call `ui.printSettings` with `{}` to inspect the printer list, selected
printer, copies, duplex, grayscale, discovery/submission status and backend receipt/error.
`{"refresh":true}` starts background discovery; poll the same command until `discovering` is
false. Set `printer` to a discovered name, integer `copies` from 1 to 999, `duplex` to
`printerDefault`, `off`, `longEdge` or `shortEdge`, and boolean `grayscale`. Invalid updates are
rejected without changing earlier settings. `ui.printSubmit` explicitly submits the current
print-ready PDF without opening a dialog; inspect `ui.printSettings` until `busy` becomes false
and check `status`/`detail`. The browser keeps its own print hook. PDF export remains separate.
GridCraft accepts the existing `file.print` sheet/pagination params on `ui.printSubmit`; the engine `file.print` command returns the PDF without spooling.