feat(shell-projection): add shim wrapper drift guard (#3448)

* feat(shell-projection): add shim wrapper drift guard

* chore(changeset): add PR 3448 changelog fragment

scripts/lint-shell-command-projection-drift.cjs

@@ -0,0 +1,57 @@
+#!/usr/bin/env node
+'use strict';
+
+/**
+ * Focused drift guard for issue #3442:
+ * prevent installer-owned inline shim/wrapper text builders from bypassing the
+ * Shell Command Projection Module seam.
+ *
+ * Scope intentionally excludes subprocess execution helpers (spawnSync /
+ * execFileSync) because those are safe internal execution primitives, not
+ * serialized shell-command rendering.
+ */
+
+const fs = require('fs');
+const path = require('path');
+
+const ROOT = path.resolve(__dirname, '..');
+const targetArg = process.argv[2] || path.join(ROOT, 'bin', 'install.js');
+const target = path.resolve(targetArg);
+const rel = path.relative(ROOT, target);
+
+let content;
+try {
+  content = fs.readFileSync(target, 'utf8');
+} catch (error) {
+  process.stderr.write(`lint-shell-command-projection-drift: failed to read ${target}: ${error.message}\n`);
+  process.exit(1);
+}
+
+const forbidden = [
+  {
+    label: 'inline cmd shim builder',
+    pattern: /@ECHO OFF\\r\\n@SETLOCAL\\r\\n@node /,
+  },
+  {
+    label: 'inline pwsh shim builder',
+    pattern: /#!\/usr\/bin\/env pwsh\\n& node /,
+  },
+  {
+    label: 'inline sh shim builder',
+    pattern: /#!\/usr\/bin\/env sh\\nexec node /,
+  },
+];
+
+const matches = forbidden.filter((rule) => rule.pattern.test(content));
+if (matches.length === 0) {
+  process.stdout.write(`ok shell-projection-drift: ${rel}\n`);
+  process.exit(0);
+}
+
+process.stderr.write(`ERROR shell-projection-drift: inline serialized shim builders found in ${rel}\n`);
+for (const match of matches) {
+  process.stderr.write(`  - ${match.label}\n`);
+}
+process.stderr.write('Route shim/wrapper rendering through get-shit-done/bin/lib/shell-command-projection.cjs\n');
+process.stderr.write('Safe subprocess execution via spawnSync/execFileSync is intentionally allowed.\n');
+process.exit(1);