Add oracle harness: verb goldens and function-level vectors

Records stdout/stderr/exit/files for every impeccable verb over a fixed
corpus and replays them against an alternate implementation. Adds a loader
hook that captures per-function call vectors from the pure engine modules.

Prepared with AI assistance (Claude Code).

tests/oracle/record.mjs

@@ -0,0 +1,18 @@
+#!/usr/bin/env node
+/**
+ * Record goldens from the JS implementation.
+ *   node tests/oracle/record.mjs            # all cases
+ *   node tests/oracle/record.mjs detect-    # only ids starting with a prefix
+ */
+import { allCases, runCase, writeGolden } from './lib.mjs';
+
+const prefix = process.argv[2] || '';
+const cases = (await allCases()).filter(c => c.id.startsWith(prefix));
+let n = 0;
+for (const c of cases) {
+  const res = runCase(c, { impl: 'js' });
+  writeGolden(c.id, res);
+  n++;
+  process.stdout.write(`recorded ${c.id} (exit ${res.exit}, ${res.stdout.length}b out, ${Object.keys(res.files).length} files)\n`);
+}
+process.stdout.write(`\n${n} goldens written\n`);