archlang-edit-plan git:20261009.bf7ba76A

Immutable. This exact content never changes and is served at /api/v1/blob/1eceb78cccdd5d4b.

---
name: archlang-edit-plan
description: Use when the user wants to change an existing ArchLang .arch floor plan, e.g. "make the bedroom 1 m wider", "add a bathroom next to the hall", "move the front door to the south wall", "merge the kitchen into the living room". Reads the plan's facts with the arch CLI, makes the smallest edit that does the job, and re-verifies. Not for writing a plan from a brief (archlang-brief-to-plan).
license: MIT
compatibility: Needs a shell with Node 18+ and the arch CLI (npx @chanmeng666/archlang, or npm i -g @chanmeng666/archlang).
---

# Edit an existing plan

Change a `.arch` file without breaking what already works. If `arch` is not on the path, write
`npx @chanmeng666/archlang` in its place.

This skill is a workflow, not a language reference. Run `arch spec` for the language and
`arch <cmd> --help` for a command's flags.

## Steps

1. **Record the starting state.** Run `arch validate plan.arch --json` and
   `arch describe plan.arch --select rooms,totals --json`. Keep both results: they are what you
   compare against at the end. If the plan already has errors, tell the user before you edit.
2. **Read only what the change touches.** `arch describe plan.arch --room <ids> --json` returns
   those rooms with the doors, windows and furniture that touch them.
   `arch describe plan.arch --select freedom --json` says which positions the author typed
   (`absolute`) and which the compiler derives. Change a typed number; a derived one moves by
   itself when the thing it depends on moves.
3. **Read the language for the forms you will write.** `arch spec`.
4. **Make the smallest edit.** Change the statements the request names and leave the rest as they
   are: same ids, same order, same comments. Do not reformat the file and do not rewrite
   statements you were not asked to change. When a room changes size, check the walls, doors,
   windows and neighbouring rooms that share its edges.
5. **Compile.** `arch compile plan.arch -o plan.svg --json`. If `ok` is false, preview the
   mechanical fixes with `arch fix plan.arch --dry-run --json` and read the diff before you apply
   them with `arch fix plan.arch --backup`.
6. **Move furniture out of the way if needed.** If the edit pushed a piece into a wall, a doorway
   or a door swing, `arch repair plan.arch -o plan.arch` moves it. Read `unresolved` for the pieces
   it could not move.
7. **Verify the change and nothing else.** Run the two commands from step 1 again. The rooms you
   meant to change differ as intended. Every other room has the same area and the same
   connections. No diagnostic is new unless the request causes it; if one is, tell the user.
8. **Refresh the sheet if the drawing grew.** `arch finish plan.arch --dry-run --json` shows what
   is missing. If it reports that the drawing no longer fits the authored `paper` or `scale`,
   `arch finish plan.arch --reissue` may replace those two statements and nothing else.

## Report to the user

- The statements you changed, as a short diff.
- Before and after for the facts the request is about (for example the room's area).
- Any new warning, and whether the request causes it.

## When something goes wrong

- Exit code `2` is a fault in the source: read the diagnostic, do not retry unchanged. `3` is a
  wrong flag: run `arch <cmd> --help`.
- `arch explain <CODE> --json` explains a diagnostic code.
- If the request needs a new door or window and you are unsure where it can go,
  `arch suggest plan.arch --json` returns candidates with the reason for each.