diff --git a/composer.json b/composer.json
index afb2557..9b2612f 100644
--- a/composer.json
+++ b/composer.json
@@ -16,12 +16,12 @@
     ],
     "require": {
         "php": ">=8.2",
-        "ext-mbstring": "*"
+        "ext-mbstring": "*",
+        "nimbuscms/nimbus": "dev-main"
     },
     "require-dev": {
         "phpstan/phpstan": "^2.2",
-        "phpunit/phpunit": "^11.0",
-        "nimbuscms/nimbus": "dev-main"
+        "phpunit/phpunit": "^11.0"
     },
     "repositories": [
         {
diff --git a/src/MarkdownPlugin.php b/src/MarkdownPlugin.php
index b1d31a5..7e970fc 100644
--- a/src/MarkdownPlugin.php
+++ b/src/MarkdownPlugin.php
@@ -23,6 +23,6 @@ final class MarkdownPlugin implements Plugin
 
     public function register(PluginContext $context): void
     {
-        $context->fieldTypes()->register(new MarkdownFieldType(), self::ID);
+        $context->fieldTypes()->register(new MarkdownFieldType());
     }
 }
diff --git a/tests/MarkdownFieldTypeTest.php b/tests/MarkdownFieldTypeTest.php
index 454acd5..1b964a8 100644
--- a/tests/MarkdownFieldTypeTest.php
+++ b/tests/MarkdownFieldTypeTest.php
@@ -34,7 +34,7 @@ private function field(array $options = [], bool $required = false): Field
     public function test_the_plugin_registers_its_field_type(): void
     {
         $registry = new FieldTypeRegistry();
-        (new MarkdownPlugin())->register(new PluginContext($registry));
+        (new MarkdownPlugin())->register(new PluginContext($registry, MarkdownPlugin::ID));
 
         self::assertTrue($registry->has('markdown'));
         self::assertSame('markdown', $registry->get('markdown')->type());
@@ -44,7 +44,7 @@ public function test_the_plugin_registers_its_field_type(): void
     public function test_the_type_appears_in_the_field_picker(): void
     {
         $registry = new FieldTypeRegistry();
-        (new MarkdownPlugin())->register(new PluginContext($registry));
+        (new MarkdownPlugin())->register(new PluginContext($registry, MarkdownPlugin::ID));
 
         self::assertArrayHasKey('markdown', $registry->choices());
         self::assertSame('Markdown', $registry->choices()['markdown']);
@@ -62,10 +62,10 @@ public function test_the_plugin_id_matches_the_composer_manifest(): void
     public function test_registering_twice_is_rejected_by_core(): void
     {
         $registry = new FieldTypeRegistry();
-        (new MarkdownPlugin())->register(new PluginContext($registry));
+        (new MarkdownPlugin())->register(new PluginContext($registry, MarkdownPlugin::ID));
 
         $this->expectException(\Nimbus\Content\DuplicateFieldType::class);
-        (new MarkdownPlugin())->register(new PluginContext($registry));
+        (new MarkdownPlugin())->register(new PluginContext($registry, MarkdownPlugin::ID));
     }
 
     // -------------------------------------------------------- normalization
@@ -125,7 +125,7 @@ public function test_max_length_counts_characters_not_bytes(): void
     public function test_required_empty_is_handled_by_core_not_here(): void
     {
         $registry = new FieldTypeRegistry();
-        (new MarkdownPlugin())->register(new PluginContext($registry));
+        (new MarkdownPlugin())->register(new PluginContext($registry, MarkdownPlugin::ID));
 
         $collection = new Collection(1, 'posts', 'Posts', '#', '', [$this->field(required: true)], ['kind' => 'collection']);
         $errors     = (new Validator($registry))->validate($collection, ['body' => $this->type->normalize('')]);
@@ -137,7 +137,7 @@ public function test_required_empty_is_handled_by_core_not_here(): void
     public function test_a_valid_required_value_passes_through_core_validation(): void
     {
         $registry = new FieldTypeRegistry();
-        (new MarkdownPlugin())->register(new PluginContext($registry));
+        (new MarkdownPlugin())->register(new PluginContext($registry, MarkdownPlugin::ID));
 
         $collection = new Collection(1, 'posts', 'Posts', '#', '', [$this->field(required: true)], ['kind' => 'collection']);
         $errors     = (new Validator($registry))->validate($collection, ['body' => $this->type->normalize('# Hello')]);
diff --git a/tests/PackageIntegrationTest.php b/tests/PackageIntegrationTest.php
new file mode 100644
index 0000000..5015fab
--- /dev/null
+++ b/tests/PackageIntegrationTest.php
@@ -0,0 +1,192 @@
+<?php
+
+declare(strict_types=1);
+
+namespace NimbusCMS\Markdown\Tests;
+
+use Nimbus\Content\Field;
+use Nimbus\Content\FieldTypeRegistry;
+use Nimbus\Content\UnknownFieldType;
+use Nimbus\Plugin\PluginDiagnostic;
+use Nimbus\Plugin\PluginLoader;
+use NimbusCMS\Markdown\MarkdownPlugin;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Proves the *package boundary*, not the field implementation.
+ *
+ * MarkdownFieldTypeTest checks that the field behaves correctly when you hand
+ * it a value. This checks something different and easy to get wrong: that a
+ * real Composer installation of this package is discovered by Nimbus's own
+ * loader, using this package's real manifest, and registers without anyone
+ * editing core.
+ *
+ * Everything here is the genuine article — the installed `composer.json`, the
+ * real `PluginLoader`, the real `FieldTypeRegistry`. Only the path to
+ * `installed.json` is synthesised, because Composer writes that file about the
+ * *root* project and this package is the root when its own tests run.
+ */
+final class PackageIntegrationTest extends TestCase
+{
+    private string $installedJson;
+
+    protected function setUp(): void
+    {
+        $this->installedJson = tempnam(sys_get_temp_dir(), 'nb-installed-') ?: '';
+    }
+
+    protected function tearDown(): void
+    {
+        @unlink($this->installedJson);
+    }
+
+    /** @return array<string,mixed> this package's actual composer manifest */
+    private function manifest(): array
+    {
+        $manifest = json_decode((string) file_get_contents(__DIR__ . '/../composer.json'), true);
+        self::assertIsArray($manifest);
+
+        return $manifest;
+    }
+
+    /**
+     * An installed.json describing this package exactly as Composer would,
+     * straight from the real manifest.
+     */
+    private function installedAs(): string
+    {
+        $manifest = $this->manifest();
+        file_put_contents($this->installedJson, json_encode([
+            'packages' => [[
+                'name'  => $manifest['name'],
+                'type'  => $manifest['type'],
+                'extra' => $manifest['extra'],
+            ]],
+        ], JSON_THROW_ON_ERROR));
+
+        return $this->installedJson;
+    }
+
+    // ------------------------------------------------------- the manifest
+
+    public function test_the_package_declares_nimbus_as_a_runtime_dependency(): void
+    {
+        $manifest = $this->manifest();
+
+        // The plugin's production classes implement Nimbus interfaces, so core
+        // is a runtime requirement. In require-dev, Composer would happily
+        // install this package without a compatible Nimbus present.
+        self::assertArrayHasKey('nimbuscms/nimbus', $manifest['require']);
+        self::assertArrayNotHasKey('nimbuscms/nimbus', $manifest['require-dev'] ?? []);
+    }
+
+    public function test_the_package_is_typed_as_a_nimbus_plugin(): void
+    {
+        self::assertSame('nimbuscms-plugin', $this->manifest()['type']);
+    }
+
+    // -------------------------------------------------- discovery to registry
+
+    public function test_composer_discovery_registers_the_field_type(): void
+    {
+        $registry    = new FieldTypeRegistry();
+        $loader      = new PluginLoader($this->installedAs());
+        $diagnostics = $loader->load($registry);
+
+        self::assertSame([], $diagnostics, 'a correctly installed package must load cleanly');
+        self::assertSame(
+            [MarkdownPlugin::ID => $this->manifest()['name']],
+            $loader->registered(),
+        );
+
+        // Registered into the *shared* registry, under this plugin's id.
+        self::assertTrue($registry->has('markdown'));
+        self::assertSame(MarkdownPlugin::ID, $registry->providerOf('markdown'));
+        self::assertArrayHasKey('markdown', $registry->choices());
+    }
+
+    public function test_core_field_types_are_untouched_by_installation(): void
+    {
+        $registry = new FieldTypeRegistry();
+        (new PluginLoader($this->installedAs()))->load($registry);
+
+        foreach (['text', 'textarea', 'number', 'boolean', 'relation'] as $core) {
+            self::assertSame('core', $registry->providerOf($core));
+        }
+    }
+
+    // ---------------------------------------------------------- disabling
+
+    public function test_disabling_the_package_leaves_the_type_unregistered(): void
+    {
+        $registry    = new FieldTypeRegistry();
+        $loader      = new PluginLoader($this->installedAs(), [MarkdownPlugin::ID => false]);
+        $diagnostics = $loader->load($registry);
+
+        self::assertSame([], $loader->registered());
+        self::assertFalse($registry->has('markdown'));
+        self::assertCount(1, $diagnostics);
+        self::assertSame(PluginDiagnostic::DISABLED, $diagnostics[0]->reason);
+        self::assertFalse($diagnostics[0]->isFailure(), 'disabled is a choice, not a fault');
+    }
+
+    public function test_with_the_package_disabled_writes_are_blocked_and_content_is_kept(): void
+    {
+        $registry = new FieldTypeRegistry();
+        (new PluginLoader($this->installedAs(), [MarkdownPlugin::ID => false]))->load($registry);
+
+        $field  = new Field('body', 'Body', 'markdown');
+        $stored = "# Still here\n\nWith **bold** text.";
+
+        // Write paths refuse the type outright...
+        try {
+            $registry->get('markdown');
+            self::fail('write paths must not resolve an unavailable type');
+        } catch (UnknownFieldType $e) {
+            self::assertSame('markdown', $e->type);
+        }
+
+        // ...while the admin degrades: the source is shown, never rewritten,
+        // and saving is refused until the package is back.
+        $fallback = $registry->forDisplay('markdown');
+        self::assertSame($stored, $fallback->normalize($stored), 'stored source must survive byte for byte');
+        self::assertNotNull($fallback->validate($field, $stored), 'saving must be blocked');
+        self::assertStringContainsString('Still here', $fallback->renderInput($field, $stored));
+        self::assertStringContainsString('markdown', $fallback->renderInput($field, $stored));
+    }
+
+    public function test_re_enabling_restores_the_field_type(): void
+    {
+        $path = $this->installedAs();
+
+        $disabled = new FieldTypeRegistry();
+        (new PluginLoader($path, [MarkdownPlugin::ID => false]))->load($disabled);
+        self::assertFalse($disabled->has('markdown'));
+
+        $enabled = new FieldTypeRegistry();
+        (new PluginLoader($path, [MarkdownPlugin::ID => true]))->load($enabled);
+
+        self::assertTrue($enabled->has('markdown'), 'flipping the switch back is all it takes');
+        self::assertSame('markdown', $enabled->get('markdown')->type());
+    }
+
+    // ----------------------------------------------------------- conflicts
+
+    public function test_a_second_package_cannot_take_this_plugins_id(): void
+    {
+        $manifest = $this->manifest();
+        file_put_contents($this->installedJson, json_encode(['packages' => [
+            ['name' => $manifest['name'], 'type' => $manifest['type'], 'extra' => $manifest['extra']],
+            ['name' => 'squatter/markdown', 'type' => 'nimbuscms-plugin', 'extra' => $manifest['extra']],
+        ]], JSON_THROW_ON_ERROR));
+
+        $registry    = new FieldTypeRegistry();
+        $loader      = new PluginLoader($this->installedJson);
+        $diagnostics = $loader->load($registry);
+
+        self::assertSame([MarkdownPlugin::ID => $manifest['name']], $loader->registered());
+        self::assertCount(1, $diagnostics);
+        self::assertSame(PluginDiagnostic::DUPLICATE_ID, $diagnostics[0]->reason);
+        self::assertSame('squatter/markdown', $diagnostics[0]->package);
+    }
+}