td: regions, local compiler, region submits; guidance for the region workflow

- td toolchain install / td_toolchain_install: downloads the compiler
  package (approved accounts) and sets up local checks; td-server
  toolchain pack builds it from the compile image.
- td_check compiles on the contributor machine only (includers: true for
  header changes, using the server include map).
- td_regions, td_claim_region, td_release_region; td_submit adds rewritten
  functions of shared regions as competing candidates.
- AGENTS.md, MCP instructions and guidance describe the region loop.

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

test/tar.test.js

@@ -0,0 +1,48 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import zlib from 'node:zlib';
+import { extractTarGz } from '../src/shared/tar.js';
+
+function header(name, size, type = '0') {
+  const h = Buffer.alloc(512);
+  h.write(name.slice(0, 100), 0);
+  h.write('0000644\0', 100);
+  h.write(size.toString(8).padStart(11, '0') + '\0', 124);
+  h.write('00000000000\0', 136);
+  h[156] = type.charCodeAt(0);
+  h.write('ustar\0', 257);
+  h.write('00', 263);
+  h.fill(' ', 148, 156);
+  let sum = 0;
+  for (const b of h) sum += b;
+  h.write(sum.toString(8).padStart(6, '0') + '\0 ', 148);
+  return h;
+}
+const pad = (b) => Buffer.concat([b, Buffer.alloc((512 - (b.length % 512)) % 512)]);
+
+test('extracts files, GNU long names and pax paths; refuses paths outside the target', async () => {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'tar-'));
+  const long = 'toolchain/vs2010sp1/vc_stdamd64/Program Files(64)/Microsoft Visual Studio 10.0/VC/bin/amd64/1033/clui.dll';
+  const pax = Buffer.from(`${`path=toolchain/pax/name.h`.length + 4} path=toolchain/pax/name.h\n`);
+  const parts = [
+    header('toolchain/', 0, '5'),
+    header('toolchain/a.txt', 5), pad(Buffer.from('hello')),
+    header('././@LongLink', long.length + 1, 'L'), pad(Buffer.from(long + '\0')), header(long.slice(0, 99), 3), pad(Buffer.from('dll')),
+    header('PaxHeader', pax.length, 'x'), pad(pax), header('short', 2), pad(Buffer.from('ok')),
+    Buffer.alloc(1024),
+  ];
+  const file = path.join(dir, 'a.tar.gz');
+  fs.writeFileSync(file, zlib.gzipSync(Buffer.concat(parts)));
+  assert.equal(await extractTarGz(file, path.join(dir, 'out')), 3);
+  assert.equal(fs.readFileSync(path.join(dir, 'out/toolchain/a.txt'), 'utf8'), 'hello');
+  assert.equal(fs.readFileSync(path.join(dir, 'out', long), 'utf8'), 'dll');
+  assert.equal(fs.readFileSync(path.join(dir, 'out/toolchain/pax/name.h'), 'utf8'), 'ok');
+
+  const evil = path.join(dir, 'evil.tar.gz');
+  fs.writeFileSync(evil, zlib.gzipSync(Buffer.concat([header('../escape.txt', 1), pad(Buffer.from('x')), Buffer.alloc(1024)])));
+  await assert.rejects(extractTarGz(evil, path.join(dir, 'out2')), /outside the target/);
+  fs.rmSync(dir, { recursive: true, force: true });
+});