chore: fixes tia when not running on root

src/Plugins/Tia.php

@@ -9,6 +9,7 @@ use Pest\Contracts\Plugins\AddsOutput;
 use Pest\Contracts\Plugins\HandlesArguments;
 use Pest\Contracts\Plugins\Terminable;
 use Pest\Exceptions\NoAffectedTestsFound;
+use Pest\Exceptions\TiaRequiresRepositoryRoot;
 use Pest\Panic;
 use Pest\Plugins\Concerns\HandleArguments;
 use Pest\Plugins\Tia\BaselineSync;
@@ -627,6 +628,13 @@ final class Tia implements AddsOutput, HandlesArguments, Terminable
     private function handleParent(array $arguments, string $projectRoot, bool $forceRebuild): array
     {
         $this->watchPatterns->useDefaults($projectRoot);
+
+        $subdirectoryPrefix = $this->gitSubdirectoryPrefix($projectRoot);
+
+        if ($subdirectoryPrefix !== null) {
+            Panic::with(new TiaRequiresRepositoryRoot($subdirectoryPrefix));
+        }
+
         $this->branch = new ChangedFiles($projectRoot)->currentBranch() ?? 'main';
 
         $fingerprint = Fingerprint::compute($projectRoot);
@@ -1643,6 +1651,27 @@ final class Tia implements AddsOutput, HandlesArguments, Terminable
         return implode(', ', array_keys($seen));
     }
 
+    /**
+     * The path from the git repository root down to $projectRoot (e.g.
+     * `laravel-app`) when the project is nested inside a larger repo, or `null`
+     * when the project root is itself the repo root (or git is unavailable).
+     * TIA requires the two to coincide: git reports and addresses paths
+     * relative to the repo root, while the dependency graph is project-relative.
+     */
+    private function gitSubdirectoryPrefix(string $projectRoot): ?string
+    {
+        $process = new Process(['git', 'rev-parse', '--show-prefix'], $projectRoot);
+        $process->run();
+
+        if (! $process->isSuccessful()) {
+            return null;
+        }
+
+        $prefix = trim($process->getOutput());
+
+        return $prefix === '' ? null : rtrim(str_replace(DIRECTORY_SEPARATOR, '/', $prefix), '/');
+    }
+
     private function composerLockDelta(string $projectRoot, string $sha): string
     {
         $current = @file_get_contents($projectRoot.'/composer.lock');