Add the Next.js web app and shared lesson content.

Move lessons out of the C sources into JSON so the web client can use the same material as the desktop app, and point release builds at desktop/.

Co-authored-by: Cursor <cursoragent@cursor.com>

tools/extract/networks.mjs

@@ -0,0 +1,97 @@
+import { readFileSync } from 'node:fs';
+import { parseArray, parseArrayInFunction, trimNulls } from '../lib/cparse.mjs';
+
+const NET_LESSONS = 27;
+
+/** `NetSlide` is positional: kicker, title, tip, line[8]. */
+function toSlide(row, label) {
+  if (!Array.isArray(row)) throw new Error(`${label}: slide is not a braced list`);
+  const [kicker, title, tip, lines] = row;
+  return {
+    kicker: kicker ?? '',
+    title: title ?? '',
+    tip: tip ?? null,
+    lines: trimNulls(lines ?? []).map((l) => String(l)),
+  };
+}
+
+/** `ChoiceQ` is positional: prompt, options[5], n_options, correct. */
+function toChoice(row, hint, label) {
+  if (!Array.isArray(row)) throw new Error(`${label}: question is not a braced list`);
+  const [prompt, options, nOptions, correct] = row;
+  const list = trimNulls(options ?? []).map((o) => String(o));
+  const n = typeof nOptions === 'number' ? nOptions : list.length;
+
+  if (typeof correct !== 'number' || correct < 0 || correct >= n) {
+    throw new Error(`${label}: correct index ${correct} out of range for ${n} options`);
+  }
+
+  const out = { kind: 'choice', prompt: String(prompt), options: list.slice(0, n), correct };
+  if (hint) out.hint = String(hint);
+  return out;
+}
+
+/** Unit 1 is the VLSM walkthrough: four scenarios plus a per-block answer key. */
+function subnetTasks(src) {
+  const tasks = parseArray(src, 'net_tasks');
+  const answers = parseArray(src, 'net_ans');
+
+  return tasks.map(([scenario, solution], i) => {
+    const rows = answers[i] ?? [];
+    const blocks = rows
+      .map(([prefix, network, broadcast, firstHost, lastHost]) => ({
+        prefix, network, broadcast, firstHost, lastHost,
+      }))
+      // A prefix of -1 marks a scenario that has no valid allocation.
+      .filter((b) => typeof b.prefix === 'number' && b.prefix > 0);
+
+    return {
+      kind: 'subnet',
+      scenario: String(scenario),
+      solution: String(solution),
+      blocks: blocks.length ? blocks : null,
+    };
+  });
+}
+
+export function extractNetworks(desktopDir) {
+  const src = readFileSync(`${desktopDir}/net.c`, 'utf8');
+  const lessons = [];
+
+  for (let n = 1; n <= NET_LESSONS; n++) {
+    const slides = parseArrayInFunction(src, `build_net_unit${n}_page`, 'slides')
+      .map((row, i) => toSlide(row, `net unit ${n} slide ${i + 1}`));
+
+    let tasks;
+    if (n === 1) {
+      tasks = [{
+        number: 1,
+        title: 'VLSM',
+        subtitleKey: 'net_ex1_title',
+        items: subnetTasks(src),
+      }];
+    } else {
+      const qs = parseArray(src, `net${n}_qs`);
+      const hints = parseArray(src, `net${n}_hints`);
+      tasks = [{
+        number: 1,
+        title: 'Quiz',
+        subtitleKey: `net_quiz${n}_head`,
+        items: qs.map((row, i) => toChoice(row, hints[i], `net unit ${n} q${i + 1}`)),
+      }];
+    }
+
+    lessons.push({
+      id: `unit-${String(n).padStart(2, '0')}`,
+      subject: 'networks',
+      number: n,
+      // Titles live in the i18n tables; the web app resolves these keys.
+      titleKey: `net_unit${n}`,
+      subtitleKey: `net_unit${n}_sub`,
+      slides,
+      tasks,
+    });
+  }
+
+  return lessons;
+}