test: harden exhaustive compatibility suites

tools/resolve-ref-root.mjs

@@ -0,0 +1,23 @@
+import { existsSync } from 'node:fs';
+import path from 'node:path';
+import { execFileSync } from 'node:child_process';
+
+export const resolveRefRoot = (repositoryRoot = process.cwd()) => {
+    if (process.env.SAMMO_REF_ROOT) {
+        return path.resolve(process.env.SAMMO_REF_ROOT);
+    }
+
+    const candidates = [path.resolve(repositoryRoot, '..', 'ref', 'sam')];
+    try {
+        const commonDir = execFileSync('git', ['rev-parse', '--path-format=absolute', '--git-common-dir'], {
+            cwd: repositoryRoot,
+            encoding: 'utf8',
+            stdio: ['ignore', 'pipe', 'ignore'],
+        }).trim();
+        candidates.push(path.resolve(path.dirname(commonDir), '..', 'ref', 'sam'));
+    } catch {
+        // The direct sibling remains the fallback outside a Git checkout.
+    }
+
+    return candidates.find((candidate) => existsSync(candidate)) ?? candidates[0];
+};