feat: module 06 parser

First Part II module. The cumulative reference adds a second engine
(src/engine/puzzle: grid, lexer, parser) beside Part I's; nouns and
properties are data in src/content/words.json, and the engine names only
IS/AND/NOT/TEXT and the base rule TEXT IS PUSH. Rules are recompiled from
the board on every change; rules() is a sorted set. Adds the M6 scenarios
and tests (rows, columns, shared IS, AND distribution, stacked text, base
rule), the HOT word as a data-only Expansion Drop, the lesson with the
Part II bridge, and the Rust LevelDef shape in harness.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

course/06-parser/tests/ts/test_06.test.ts

@@ -0,0 +1,78 @@
+// Module 6: Grid, lexer and parser. Each test matches a heading in scenarios.md.
+import { expect, test } from "vitest";
+import { newBaba, type Baba } from "../src/harness";
+
+/** An empty level `width` wide and `height` high. */
+const emptyLevel = (width: number, height: number) => ({ width, height, objects: [] });
+
+/** Place one text object per word: `[word, x, y]`. */
+function write(b: Baba, words: [string, number, number][]): void {
+  for (const [word, x, y] of words) b.place(`text:${word}`, x, y);
+}
+
+test("test_06_horizontal_rule", () => {
+  const b = newBaba({
+    width: 5,
+    height: 3,
+    objects: [
+      { kind: "text:BABA", x: 0, y: 0 },
+      { kind: "text:IS", x: 1, y: 0 },
+      { kind: "text:YOU", x: 2, y: 0 },
+      { kind: "baba", x: 3, y: 2 },
+      { kind: "text:YOU", x: 0, y: 2 },
+      { kind: "text:IS", x: 1, y: 2 },
+      { kind: "text:FLAG", x: 2, y: 2 },
+    ],
+  });
+
+  expect(b.rules()).toEqual(["BABA IS YOU", "TEXT IS PUSH"]);
+});
+
+test("test_06_crossword_shared_is", () => {
+  const b = newBaba(emptyLevel(3, 3));
+  write(b, [
+    ["BABA", 0, 1],
+    ["IS", 1, 1],
+    ["YOU", 2, 1],
+    ["FLAG", 1, 0],
+  ]);
+
+  expect(b.rules()).toEqual(["BABA IS YOU", "TEXT IS PUSH"]);
+
+  b.place("text:WIN", 1, 2);
+
+  expect(b.rules()).toEqual(["BABA IS YOU", "FLAG IS WIN", "TEXT IS PUSH"]);
+});
+
+test("test_06_and_distributes", () => {
+  const b = newBaba(emptyLevel(7, 1));
+  write(b, [
+    ["BABA", 0, 0],
+    ["AND", 1, 0],
+    ["ROCK", 2, 0],
+    ["IS", 3, 0],
+    ["PUSH", 4, 0],
+    ["AND", 5, 0],
+    ["STOP", 6, 0],
+  ]);
+
+  expect(b.rules()).toEqual(["BABA IS PUSH", "BABA IS STOP", "ROCK IS PUSH", "ROCK IS STOP", "TEXT IS PUSH"]);
+});
+
+test("test_06_stacked_text_all_combinations", () => {
+  const b = newBaba(emptyLevel(3, 1));
+  write(b, [
+    ["BABA", 0, 0],
+    ["ROCK", 0, 0],
+    ["IS", 1, 0],
+    ["YOU", 2, 0],
+  ]);
+
+  expect(b.rules()).toEqual(["BABA IS YOU", "ROCK IS YOU", "TEXT IS PUSH"]);
+});
+
+test("test_06_default_text_is_push", () => {
+  const b = newBaba({ width: 3, height: 3, objects: [{ kind: "baba", x: 1, y: 1 }] });
+
+  expect(b.rules()).toEqual(["TEXT IS PUSH"]);
+});