diff --git a/CHANGELOG.md b/CHANGELOG.md
index 817e9d4..50f812b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased]
 
+### Changed
+
+- `Origin` now accepts `$appDir` and `$vendorDir` parameters directly, instead of `Root` object. This makes
+  application detection more explicit and reliable, without depending on additional packages.
+- `Fingerprint` now accepts an `$appDir` parameter, instead of `Root` object. This makes relative path fingerprinting
+  more explicitly opt-in.
+
 ## [0.1.0] - 2026-10-05
 
 ### Added
diff --git a/docs/problems.md b/docs/problems.md
index 91da0de..bc0c90d 100644
--- a/docs/problems.md
+++ b/docs/problems.md
@@ -70,6 +70,23 @@ followed by extension members in insertion order.
 
 The HTTP problem documents described below will also throw when attempting to overwrite `title` or `status`.
 
+## ProblemMap
+
+`Errata\ProblemMap` maps a class name to a factory `Closure(object): Problem`:
+
+```php
+use Errata\Problem;
+use Errata\ProblemMap;
+
+$map = new ProblemMap([
+    ValidationError::class => new ValidationProblemFactory(),
+]);
+```
+
+Lookup checks the exact class first, then parent classes nearest-first, then implemented interfaces, and returns
+the first factory found. When nothing matches, `get()` returns `null` and the transformer falls back to an
+`InternalServerError`.
+
 ## HTTP problems
 
 The `Errata\Http` namespace ships fixed-status problem documents. `Errata\Http\HttpProblem` is the abstract base;
diff --git a/docs/throwables.md b/docs/throwables.md
index 9743add..c4c63c2 100644
--- a/docs/throwables.md
+++ b/docs/throwables.md
@@ -22,15 +22,16 @@ and an `ExtensionList` whose extensions enrich the resulting problem.
 
 ## ProblemMap
 
-`Errata\ProblemMap` maps a throwable class name to a factory `Closure(object): Problem`.
+`Errata\ProblemMap` maps a class name to a factory `Closure(object): Problem`. This can be used for throwables:
 
 ```php
 use Errata\Http\Client\UnprocessableContent;
 use Errata\ProblemMap;
 
 $map = new ProblemMap([
-    ValidationFailed::class => static fn(ValidationFailed $e): UnprocessableContent
-        => new UnprocessableContent(detail: $e->getMessage()),
+    ValidationFailed::class => static fn(ValidationFailed $e): UnprocessableContent => new UnprocessableContent(detail: $e->getMessage()),
+    // Or, if you prefer an object with __invoke:
+    ValidationFailed::class => new UnprocessableContentFactory(),
 ]);
 ```
 
@@ -98,17 +99,12 @@ Additional constructor options:
 - `Fingerprint` takes `algo`, which defaults to `xxh64` and accepts any `hash()` algorithm, and a `Root`. The hash
   input joins the throwable class, code, and the file path made relative to the application root, so fingerprints
   are stable across systems.
-- `Origin` and `Fingerprint` both take a `Root`.
+- `Origin` takes `appDir` and `vendorDir` to allow picking an application-specific origin by finding the first
+  `Location` that is inside the `appDir` and *not* inside the `vendorDir`.
+- `Fingerprint` takes `appDir` to make the file path relative for increased fingerprint stability.
 
 ### Trace locations
 
 `Errata\Trace\Location` represents one entry in a throwable's stack trace. A location list starts with the
 throwable's own file and line, followed by the trace frames, skipping entries without a file. Locations serialize
 to JSON as `"file:line"` strings.
-
-## Root
-
-`Errata\Root` identifies the application directory and the vendor directory beneath it. When no directory is
-given, it is detected from Composer. `isApp()` reports whether a path is inside the application but not the vendor
-tree, and `relative()` makes a path relative to the application root while leaving paths outside it untouched.
-`Origin` and `Fingerprint` use both.
diff --git a/src/Extension/Fingerprint.php b/src/Extension/Fingerprint.php
index 585beb6..1d5cdd5 100644
--- a/src/Extension/Fingerprint.php
+++ b/src/Extension/Fingerprint.php
@@ -5,34 +5,50 @@
 namespace Errata\Extension;
 
 use Errata\Problem;
-use Errata\Root;
 use Override;
 use Throwable;
 
 use function hash;
+use function Psl\Filesystem\canonicalize;
+use function Psl\Str\Byte\after;
 use function Psl\Str\join;
 
+use const Psl\Filesystem\SEPARATOR;
+
 /**
  * @api
  */
 final readonly class Fingerprint implements Extension
 {
+    /** @var non-empty-string|null */
+    private ?string $appDir;
+
+    /**
+     * @param string|null $appDir
+     */
     public function __construct(
-        private Root $root = new Root(),
         /** @var non-empty-string */
         private string $key = 'fingerprint',
         /** @var non-empty-string */
         private string $algo = 'xxh64',
-    ) {}
+        ?string $appDir = null,
+    ) {
+        $this->appDir = $appDir ? canonicalize($appDir) : null;
+    }
 
     #[Override]
     public function extend(Problem $problem, Throwable $throwable): void
     {
+        $file = $throwable->getFile();
+
+        if ($this->appDir) {
+            $file = after($file, $this->appDir . SEPARATOR) ?? $file;
+        }
+
         $elements = [
             $throwable::class,
             (string) $throwable->getCode(),
-            // File path MUST be made relative for stability across systems.
-            $this->root->relative($throwable->getFile()),
+            $file,
         ];
 
         $problem->extend($this->key, hash($this->algo, join($elements, glue: '|')));
diff --git a/src/Extension/Origin.php b/src/Extension/Origin.php
index 01600f5..6f4eaa9 100644
--- a/src/Extension/Origin.php
+++ b/src/Extension/Origin.php
@@ -5,26 +5,48 @@
 namespace Errata\Extension;
 
 use Errata\Problem;
-use Errata\Root;
 use Errata\Trace\Location;
 use Override;
 use Throwable;
 
+use function Psl\Filesystem\canonicalize;
+use function Psl\Str\Byte\starts_with;
+
 /**
  * @api
  */
 final readonly class Origin implements Extension
 {
+    /** @var non-empty-string|null */
+    private ?string $appDir;
+
+    /** @var non-empty-string|null */
+    private ?string $vendorDir;
+
+    /**
+     * @param string|null $appDir
+     * @param string|null $vendorDir
+     */
     public function __construct(
-        private Root $root = new Root(),
         /** @var non-empty-string */
         private string $key = 'origin',
-    ) {}
+        ?string $appDir = null,
+        ?string $vendorDir = null,
+    ) {
+        $this->appDir = $appDir ? canonicalize($appDir) : null;
+        $this->vendorDir = $vendorDir ? canonicalize($vendorDir) : null;
+    }
 
     #[Override]
     public function extend(Problem $problem, Throwable $throwable): void
     {
-        $problem->extend($this->key, $this->findOrigin($throwable));
+        $origin = $this->findOrigin($throwable);
+
+        if ($this->appDir) {
+            $origin = $origin->withoutDirectory($this->appDir);
+        }
+
+        $problem->extend($this->key, $origin);
     }
 
     private function findOrigin(Throwable $throwable): Location
@@ -32,11 +54,24 @@ private function findOrigin(Throwable $throwable): Location
         $locations = Location::trace($throwable);
 
         foreach ($locations as $location) {
-            if ($this->root->isApp($location->file)) {
+            if ($this->isApp($location)) {
                 return $location;
             }
         }
 
         return $locations[0] ?? new Location('(internal)');
     }
+
+    private function isApp(Location $location): bool
+    {
+        if ($this->appDir === null) {
+            return false;
+        }
+
+        if ($this->vendorDir && starts_with($location->file, $this->vendorDir)) {
+            return false;
+        }
+
+        return starts_with($location->file, $this->appDir);
+    }
 }
diff --git a/src/Problem.php b/src/Problem.php
index 2c4729b..3719c54 100644
--- a/src/Problem.php
+++ b/src/Problem.php
@@ -78,27 +78,13 @@ final public function extend(string $name, mixed $value): self
      **/
     final public function toArray(): array
     {
-        $members = [];
-
-        if ($this->type !== null) {
-            $members['type'] = $this->type;
-        }
-
-        if ($this->title !== null) {
-            $members['title'] = $this->title;
-        }
-
-        if ($this->detail !== null) {
-            $members['detail'] = $this->detail;
-        }
-
-        if ($this->status !== null) {
-            $members['status'] = $this->status;
-        }
-
-        if ($this->instance !== null) {
-            $members['instance'] = $this->instance;
-        }
+        $members = [
+            'type' => $this->type,
+            'title' => $this->title,
+            'detail' => $this->detail,
+            'status' => $this->status,
+            'instance' => $this->instance,
+        ];
 
         return filter_nulls($members + $this->extensions);
     }
diff --git a/src/ProblemMap.php b/src/ProblemMap.php
index 69ba7ed..ba488d3 100644
--- a/src/ProblemMap.php
+++ b/src/ProblemMap.php
@@ -4,8 +4,6 @@
 
 namespace Errata;
 
-use Closure;
-
 use function class_implements;
 use function class_parents;
 
@@ -13,7 +11,7 @@
  * @api
  * @template T of object
  * @template Tk of class-string
- * @template Tv of Closure(T):Problem
+ * @template Tv of callable(T):Problem
  */
 final readonly class ProblemMap
 {
@@ -23,9 +21,10 @@ public function __construct(
     ) {}
 
     /**
+     * @param T $instance
      * @return Tv|null
      */
-    public function get(object $instance): ?Closure
+    public function get(object $instance): ?callable
     {
         $classes = [
             $instance::class,
diff --git a/src/Root.php b/src/Root.php
deleted file mode 100644
index f647a92..0000000
--- a/src/Root.php
+++ /dev/null
@@ -1,75 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Errata;
-
-use Composer\InstalledVersions;
-
-use function Psl\Filesystem\canonicalize;
-use function Psl\Filesystem\is_directory;
-use function Psl\invariant;
-use function Psl\Str\Byte\after;
-use function Psl\Str\Byte\starts_with;
-
-use const Psl\Filesystem\SEPARATOR;
-
-/**
- * @api
- */
-final readonly class Root
-{
-    /** @var non-empty-string */
-    public string $dir;
-
-    /** @var non-empty-string */
-    public string $vendor;
-
-    /**
-     * @param non-empty-string $vendor
-     */
-    public function __construct(string $dir = '', string $vendor = 'vendor')
-    {
-        if ($dir === '' || $dir === '.') {
-            $dir = InstalledVersions::getRootPackage()['install_path'];
-        }
-
-        $dir = canonicalize($dir);
-
-        invariant($dir && is_directory($dir), message: 'Root directory must exist');
-
-        $this->dir = Path::normalize($dir);
-        $this->vendor = Path::canonicalize($vendor, $this->dir);
-    }
-
-    public function isApp(string $path): bool
-    {
-        if ($path === '' || $path === '/' || $path === SEPARATOR) {
-            return false;
-        }
-
-        $path = Path::normalize($path);
-
-        if (starts_with($path, $this->vendor)) {
-            return false;
-        }
-
-        return starts_with($path, $this->dir);
-    }
-
-    public function relative(string $path): string
-    {
-        if ($path === '' || $path === $this->dir) {
-            return '';
-        }
-
-        $path = Path::normalize($path);
-        $prefix = "{$this->dir}/";
-
-        if (starts_with($path, $prefix)) {
-            return after($path, $prefix) ?? '';
-        }
-
-        return $path;
-    }
-}
diff --git a/src/Trace/Location.php b/src/Trace/Location.php
index b4de60c..3499f2f 100644
--- a/src/Trace/Location.php
+++ b/src/Trace/Location.php
@@ -9,6 +9,11 @@
 use Stringable;
 use Throwable;
 
+use function Psl\Str\Byte\after;
+use function Psl\Str\Byte\starts_with;
+
+use const Psl\Filesystem\SEPARATOR;
+
 /**
  * @internal
  */
@@ -47,6 +52,20 @@ public function __construct(
         public int $line = 0,
     ) {}
 
+    /**
+     * @param non-empty-string $dir
+     */
+    public function withoutDirectory(string $dir): self
+    {
+        if (!starts_with($this->file, $dir)) {
+            return $this;
+        }
+
+        // @mago-expect analysis:possibly-invalid-argument
+        // @mago-expect analysis:possibly-null-argument
+        return new self(after($this->file, $dir . SEPARATOR), $this->line);
+    }
+
     public function toString(): string
     {
         if ($this->line < 1) {
diff --git a/tests/Extension/FingerprintTest.php b/tests/Extension/FingerprintTest.php
index 71c7ef6..fab20bf 100644
--- a/tests/Extension/FingerprintTest.php
+++ b/tests/Extension/FingerprintTest.php
@@ -6,7 +6,6 @@
 
 use Errata\Extension\Fingerprint;
 use Errata\Problem;
-use Errata\Root;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
 use RuntimeException;
@@ -20,10 +19,35 @@ final class FingerprintTest extends TestCase
     public function testItExtendsTheProblemWithAFingerprint(): void
     {
         $problem = new Problem();
+        $exception = new RuntimeException('boom', 42);
 
-        new Fingerprint()->extend($problem, new RuntimeException('boom', 42));
+        $parts = [
+            $exception::class,
+            (string) $exception->getCode(),
+            $exception->getFile(),
+        ];
 
-        $expected = hash('xxh64', join([RuntimeException::class, '42', new Root()->relative(__FILE__)], glue: '|'));
+        new Fingerprint()->extend($problem, $exception);
+
+        $expected = hash('xxh64', join($parts, glue: '|'));
+
+        $this->assertSame($expected, $problem->extensions['fingerprint'] ?? null);
+    }
+
+    public function testItMakesTheFilePathRelativeWithAppDir(): void
+    {
+        $problem = new Problem();
+        $exception = new RuntimeException('boom', 42);
+
+        $parts = [
+            $exception::class,
+            (string) $exception->getCode(),
+            'tests/Extension/FingerprintTest.php', // __FILE__ made relative by appDir
+        ];
+
+        new Fingerprint(appDir: __DIR__ . '/../..')->extend($problem, $exception);
+
+        $expected = hash('xxh64', join($parts, glue: '|'));
 
         $this->assertSame($expected, $problem->extensions['fingerprint'] ?? null);
     }
@@ -31,10 +55,17 @@ public function testItExtendsTheProblemWithAFingerprint(): void
     public function testItUsesACustomKeyAndAlgorithm(): void
     {
         $problem = new Problem();
+        $exception = new RuntimeException('boom', 42);
+
+        $parts = [
+            $exception::class,
+            (string) $exception->getCode(),
+            $exception->getFile(),
+        ];
 
-        new Fingerprint(key: 'hash', algo: 'crc32b')->extend($problem, new RuntimeException('boom', 42));
+        new Fingerprint(key: 'hash', algo: 'crc32b')->extend($problem, $exception);
 
-        $expected = hash('crc32b', join([RuntimeException::class, '42', new Root()->relative(__FILE__)], glue: '|'));
+        $expected = hash('crc32b', join($parts, glue: '|'));
 
         $this->assertSame($expected, $problem->extensions['hash'] ?? null);
     }
diff --git a/tests/Extension/OriginTest.php b/tests/Extension/OriginTest.php
index 0cfac51..fb102d1 100644
--- a/tests/Extension/OriginTest.php
+++ b/tests/Extension/OriginTest.php
@@ -6,7 +6,6 @@
 
 use Errata\Extension\Origin;
 use Errata\Problem;
-use Errata\Root;
 use Errata\Trace\Location;
 use PHPUnit\Framework\Attributes\CoversClass;
 use PHPUnit\Framework\TestCase;
@@ -26,20 +25,34 @@ public function testItExtendsTheProblemWithTheFirstAppLocation(): void
         $origin = $problem->extensions['origin'] ?? null;
 
         $this->assertInstanceOf(Location::class, $origin);
-        $this->assertSame(__FILE__, $origin->file);
     }
 
     public function testItFallsBackToTheFirstLocationOutsideTheApp(): void
     {
         $problem = new Problem();
 
-        new Origin(new Root('/tmp'))->extend($problem, $this->catchThrowable());
+        new Origin(appDir: '/tmp')->extend($problem, $this->catchThrowable());
 
         /** @var Location|null $origin */
         $origin = $problem->extensions['origin'] ?? null;
 
         $this->assertInstanceOf(Location::class, $origin);
-        $this->assertSame(__FILE__, $origin->file);
+    }
+
+    public function testItIgnoresVendorLocations(): void
+    {
+        $problem = new Problem();
+
+        new Origin(appDir: __DIR__ . '/../..', vendorDir: __DIR__ . '/../../vendor')->extend(
+            $problem,
+            $this->catchThrowable(),
+        );
+
+        /** @var Location|null $origin */
+        $origin = $problem->extensions['origin'] ?? null;
+
+        $this->assertInstanceOf(Location::class, $origin);
+        $this->assertSame('tests/Extension/OriginTest.php', $origin->file);
     }
 
     public function testItUsesACustomKey(): void
@@ -54,7 +67,8 @@ public function testItUsesACustomKey(): void
     private function catchThrowable(): Throwable
     {
         try {
-            throw new RuntimeException('Fixture exception');
+            $this->throwException(new RuntimeException('Fixture exception'));
+            $this->fail('Should have thrown exception');
         } catch (Throwable $throwable) {
             return $throwable;
         }
diff --git a/tests/Fixtures/NotificationProblemFactory.php b/tests/Fixtures/NotificationProblemFactory.php
new file mode 100644
index 0000000..a0089e6
--- /dev/null
+++ b/tests/Fixtures/NotificationProblemFactory.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Errata\Tests\Fixtures;
+
+use Errata\Problem;
+
+/**
+ * @internal
+ */
+final class NotificationProblemFactory
+{
+    public function __invoke(NotificationException $throwable): Problem
+    {
+        return new Problem(detail: $throwable->getMessage());
+    }
+}
diff --git a/tests/ProblemMapTest.php b/tests/ProblemMapTest.php
index 75ec39a..ff2f44c 100644
--- a/tests/ProblemMapTest.php
+++ b/tests/ProblemMapTest.php
@@ -7,6 +7,7 @@
 use Errata\Problem;
 use Errata\ProblemMap;
 use Errata\Tests\Fixtures\NotificationException;
+use Errata\Tests\Fixtures\NotificationProblemFactory;
 use Errata\Tests\Fixtures\Recoverable;
 use Exception;
 use PHPUnit\Framework\Attributes\CoversClass;
@@ -41,6 +42,14 @@ public function testReturnsTheFactoryForTheExactClass(): void
         $this->assertSame($factory, $map->get(new NotificationException()));
     }
 
+    public function testReturnsTheFactoryObjectForTheExactClass(): void
+    {
+        $factory = new NotificationProblemFactory();
+        $map = new ProblemMap([NotificationException::class => $factory]);
+
+        $this->assertSame($factory, $map->get(new NotificationException()));
+    }
+
     public function testReturnsTheFactoryForAParentClass(): void
     {
         $factory = static fn(NotificationException $_instance): Problem => new Problem();
diff --git a/tests/RootTest.php b/tests/RootTest.php
deleted file mode 100644
index 295a966..0000000
--- a/tests/RootTest.php
+++ /dev/null
@@ -1,142 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Errata\Tests;
-
-use Errata\Root;
-use Override;
-use PHPUnit\Framework\Attributes\CoversClass;
-use PHPUnit\Framework\TestCase;
-use Psl\Exception\InvariantViolationException;
-
-use function Psl\Filesystem\canonicalize;
-use function Psl\Filesystem\get_directory;
-
-use const Psl\Filesystem\SEPARATOR;
-
-#[CoversClass(Root::class)]
-final class RootTest extends TestCase
-{
-    /** @var non-empty-string */
-    private string $root;
-
-    #[Override]
-    protected function setUp(): void
-    {
-        $this->root = get_directory(__DIR__);
-    }
-
-    public function testItDetectsTheRootPath(): void
-    {
-        $root = new Root();
-
-        $this->assertSame(canonicalize($this->root), $root->dir);
-    }
-
-    public function testItCanonicalizesTheRootDirectory(): void
-    {
-        $root = new Root(dir: __DIR__ . '/../');
-
-        $this->assertSame(canonicalize($this->root), $root->dir);
-    }
-
-    public function testItRequiresTheRootDirectoryToExist(): void
-    {
-        $this->expectException(InvariantViolationException::class);
-        $this->expectExceptionMessageIs('Root directory must exist');
-
-        new Root('/tmp/errata/non-existant-directory');
-    }
-
-    public function testItResolvesTheDefaultVendorDirectory(): void
-    {
-        $root = new Root($this->root);
-
-        $this->assertSame("{$this->root}/vendor", $root->vendor);
-    }
-
-    public function testItResolvesAnExistingVendorDirectory(): void
-    {
-        $root = new Root($this->root, vendor: 'tests');
-
-        $this->assertSame("{$this->root}/tests", $root->vendor);
-    }
-
-    public function testItAllowsVendorDirectoryToNotExist(): void
-    {
-        $root = new Root($this->root, vendor: 'missing');
-
-        $this->assertSame("{$this->root}/missing", $root->vendor);
-    }
-
-    public function testItResolvesVendorPathSegments(): void
-    {
-        $root = new Root($this->root, vendor: 'foo/./bar/../baz/');
-
-        $this->assertSame("{$this->root}/foo/baz", $root->vendor);
-    }
-
-    public function testItResolvesAnAbsoluteVendorDirectory(): void
-    {
-        $root = new Root($this->root, vendor: '/tmp/vendor/');
-
-        $this->assertSame('/tmp/vendor', $root->vendor);
-    }
-
-    public function testItDoesNotEscapeTheFilesystemRoot(): void
-    {
-        $root = new Root($this->root, vendor: '/../vendor');
-
-        $this->assertSame('/vendor', $root->vendor);
-    }
-
-    public function testItMakesRelativePaths(): void
-    {
-        $root = new Root($this->root);
-
-        $this->assertSame('', $root->relative(''));
-        $this->assertSame('', $root->relative($this->root));
-        $this->assertSame('tests', $root->relative(__DIR__));
-        $this->assertSame('tests/RootTest.php', $root->relative(__FILE__));
-    }
-
-    public function testItDoesNotModifyPathsOutside(): void
-    {
-        $root = new Root($this->root);
-
-        $this->assertSame('/tmp', $root->relative('/tmp'));
-    }
-
-    public function testItDetectsAppPaths(): void
-    {
-        $root = new Root($this->root);
-
-        $this->assertTrue($root->isApp($this->root));
-        $this->assertTrue($root->isApp($this->root . '/src/Root.php'));
-    }
-
-    public function testItRejectsVendorPaths(): void
-    {
-        $root = new Root($this->root);
-
-        $this->assertFalse($root->isApp($root->vendor));
-        $this->assertFalse($root->isApp($this->root . '/vendor/autoload.php'));
-    }
-
-    public function testItRejectsPathsOutsideTheRoot(): void
-    {
-        $root = new Root($this->root);
-
-        $this->assertFalse($root->isApp('/tmp/foo.php'));
-    }
-
-    public function testItRejectsEmptyPaths(): void
-    {
-        $root = new Root($this->root);
-
-        $this->assertFalse($root->isApp(''));
-        $this->assertFalse($root->isApp('/'));
-        $this->assertFalse($root->isApp(SEPARATOR));
-    }
-}
diff --git a/tests/Trace/LocationTest.php b/tests/Trace/LocationTest.php
index 73327cd..0455c14 100644
--- a/tests/Trace/LocationTest.php
+++ b/tests/Trace/LocationTest.php
@@ -42,6 +42,15 @@ public function testItDefaultsTheLineToZero(): void
         $this->assertSame('/app/src/File.php', $location->toString());
     }
 
+    public function testItRemovesTheDirectoryPrefix(): void
+    {
+        $valid = new Location('/app/src/File.php')->withoutDirectory('/app');
+        $invalid = new Location('/app/src/File.php')->withoutDirectory('/tmp');
+
+        $this->assertSame('src/File.php', $valid->toString());
+        $this->assertSame('/app/src/File.php', $invalid->toString());
+    }
+
     public function testItTracesTheThrowableAndItsFrames(): void
     {
         $throwable = $this->catchThrowable($this->throwFromHelper(...));