feat: add /update skill for pulling upstream changes (#372)

Interactive skill that guides Claude through fetching upstream NanoClaw,
previewing changes, merging with customizations, running migrations, and
verifying the result. Includes:

- SKILL.md with 9-step update flow
- fetch-upstream.sh: detects remote, fetches, extracts tracked paths
- run-migrations.ts: discovers and runs version-ordered migrations
- post-update.ts: clears backup after conflict resolution
- update-core.ts: adds --json and --preview-only flags
- BASE_INCLUDES moved to constants.ts as single source of truth
- 16 new tests covering fetch, migrations, and CLI flags

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

scripts/run-migrations.ts

@@ -0,0 +1,104 @@
+#!/usr/bin/env tsx
+import { execFileSync, execSync } from 'child_process';
+import fs from 'fs';
+import path from 'path';
+
+import { compareSemver } from '../skills-engine/state.js';
+
+// Resolve tsx binary once to avoid npx race conditions across migrations
+function resolveTsx(): string {
+  // Check local node_modules first
+  const local = path.resolve('node_modules/.bin/tsx');
+  if (fs.existsSync(local)) return local;
+  // Fall back to whichever tsx is in PATH
+  try {
+    return execSync('which tsx', { encoding: 'utf-8' }).trim();
+  } catch {
+    return 'npx'; // last resort
+  }
+}
+
+const tsxBin = resolveTsx();
+
+const fromVersion = process.argv[2];
+const toVersion = process.argv[3];
+const newCorePath = process.argv[4];
+
+if (!fromVersion || !toVersion || !newCorePath) {
+  console.error(
+    'Usage: tsx scripts/run-migrations.ts <from-version> <to-version> <new-core-path>',
+  );
+  process.exit(1);
+}
+
+interface MigrationResult {
+  version: string;
+  success: boolean;
+  error?: string;
+}
+
+const results: MigrationResult[] = [];
+
+// Look for migrations in the new core
+const migrationsDir = path.join(newCorePath, 'migrations');
+
+if (!fs.existsSync(migrationsDir)) {
+  console.log(
+    JSON.stringify({ migrationsRun: 0, results: [] }, null, 2),
+  );
+  process.exit(0);
+}
+
+// Discover migration directories (version-named)
+const entries = fs.readdirSync(migrationsDir, { withFileTypes: true });
+const migrationVersions = entries
+  .filter((e) => e.isDirectory() && /^\d+\.\d+\.\d+$/.test(e.name))
+  .map((e) => e.name)
+  .filter(
+    (v) =>
+      compareSemver(v, fromVersion) > 0 && compareSemver(v, toVersion) <= 0,
+  )
+  .sort(compareSemver);
+
+const projectRoot = process.cwd();
+
+for (const version of migrationVersions) {
+  const migrationIndex = path.join(migrationsDir, version, 'index.ts');
+  if (!fs.existsSync(migrationIndex)) {
+    results.push({
+      version,
+      success: false,
+      error: `Migration ${version}/index.ts not found`,
+    });
+    continue;
+  }
+
+  try {
+    const tsxArgs = tsxBin.endsWith('npx')
+      ? ['tsx', migrationIndex, projectRoot]
+      : [migrationIndex, projectRoot];
+    execFileSync(tsxBin, tsxArgs, {
+      stdio: 'pipe',
+      cwd: projectRoot,
+      timeout: 120_000,
+    });
+    results.push({ version, success: true });
+  } catch (err) {
+    const message =
+      err instanceof Error ? err.message : String(err);
+    results.push({ version, success: false, error: message });
+  }
+}
+
+console.log(
+  JSON.stringify(
+    { migrationsRun: results.length, results },
+    null,
+    2,
+  ),
+);
+
+// Exit with error if any migration failed
+if (results.some((r) => !r.success)) {
+  process.exit(1);
+}