diff --git a/app/Modules/Comments/FileCommentPolicy.php b/app/Modules/Comments/FileCommentPolicy.php
index 67c64dee..420ef2f1 100644
--- a/app/Modules/Comments/FileCommentPolicy.php
+++ b/app/Modules/Comments/FileCommentPolicy.php
@@ -7,6 +7,7 @@ namespace App\Modules\Comments;
 use App\Models\User;
 use App\Modules\Comments\Access\VisibleCommentScope;
 use App\Modules\Comments\Models\FileComment;
+use App\Modules\Files\Access\StaffLibraryScope;
 use Illuminate\Support\Facades\Gate;
 
 /**
@@ -20,6 +21,7 @@ class FileCommentPolicy
     public function __construct(
         private readonly VisibleCommentScope $scope,
         private readonly CommentingRules $rules,
+        private readonly StaffLibraryScope $library,
     ) {}
 
     public function view(User $user, FileComment $comment): bool
@@ -44,16 +46,38 @@ class FileCommentPolicy
 
     public function delete(User $user, FileComment $comment): bool
     {
-        if ($this->moderate($user)) {
+        if ($this->moderate($user, $comment)) {
             return true;
         }
 
         return $comment->author_id === $user->id && $this->withinEditWindow($comment);
     }
 
-    public function moderate(User $user): bool
+    /**
+     * Called both ways: with a comment, to decide about that one, and
+     * against the class, to ask whether this user moderates at all (the
+     * queue's own gate, and the affordances that offer it).
+     *
+     * The library boundary belongs here rather than in each caller. Named
+     * against the class it cannot be applied — there is no file to weigh —
+     * so that form answers the coarser question and every caller holding a
+     * comment should pass it.
+     */
+    public function moderate(User $user, ?FileComment $comment = null): bool
     {
-        return $user->isStaff() && $user->can('moderate_comments');
+        if (! $user->isStaff() || ! $user->can('moderate_comments')) {
+            return false;
+        }
+
+        if ($comment === null || ! $user->isClientScoped()) {
+            return true;
+        }
+
+        // By file id rather than through the relation: a file soft-deleted
+        // out from under its comments resolves to null there, and the
+        // answer for a scoped moderator is the same either way — it is not
+        // in their library. Unscoped staff never reach this line.
+        return $this->library->files($user)->whereKey($comment->file_id)->exists();
     }
 
     private function withinEditWindow(FileComment $comment): bool
diff --git a/app/Modules/Comments/Http/Controllers/Api/CommentModerationController.php b/app/Modules/Comments/Http/Controllers/Api/CommentModerationController.php
index 27d524f1..fdaea2d1 100644
--- a/app/Modules/Comments/Http/Controllers/Api/CommentModerationController.php
+++ b/app/Modules/Comments/Http/Controllers/Api/CommentModerationController.php
@@ -70,9 +70,9 @@ class CommentModerationController extends Controller
     {
         $viewer = $request->user();
         assert($viewer !== null);
-        Gate::forUser($viewer)->authorize('moderate', FileComment::class);
-        // Moderation rights are not a way around the library boundary.
-        abort_unless($this->library->allowsFile($viewer, $comment->file), 403);
+        // Moderation rights are not a way around the library boundary; the
+        // policy weighs the comment's file, so name the comment.
+        Gate::authorize('moderate', $comment);
 
         $this->comments->approve($comment, $viewer);
 
diff --git a/app/Modules/Comments/Http/Controllers/CommentsController.php b/app/Modules/Comments/Http/Controllers/CommentsController.php
index fffc0612..cf2e2ecc 100644
--- a/app/Modules/Comments/Http/Controllers/CommentsController.php
+++ b/app/Modules/Comments/Http/Controllers/CommentsController.php
@@ -11,7 +11,6 @@ use App\Modules\Comments\CommentPresenter;
 use App\Modules\Comments\CommentVisibility;
 use App\Modules\Comments\FileComments;
 use App\Modules\Comments\Models\FileComment;
-use App\Modules\Files\Access\StaffLibraryScope;
 use App\Modules\Platform\Localization\LocalDay;
 use App\Modules\Platform\Localization\TimezoneRegistry;
 use Carbon\Carbon;
@@ -44,7 +43,6 @@ class CommentsController extends Controller
 
     public function __construct(
         private readonly FileComments $comments,
-        private readonly StaffLibraryScope $library,
         private readonly CommentPresenter $presenter,
         private readonly VisibleCommentScope $scope,
         private readonly TimezoneRegistry $timezones,
@@ -95,9 +93,9 @@ class CommentsController extends Controller
     {
         $viewer = $request->user();
         assert($viewer !== null);
-        Gate::forUser($viewer)->authorize('moderate', FileComment::class);
-        // Moderation rights are not a way around the library boundary.
-        abort_unless($this->library->allowsFile($viewer, $comment->file), 403);
+        // Moderation rights are not a way around the library boundary; the
+        // policy weighs the comment's file, so name the comment.
+        Gate::forUser($viewer)->authorize('moderate', $comment);
 
         $this->comments->approve($comment, $viewer);
 
@@ -113,7 +111,6 @@ class CommentsController extends Controller
         $viewer = $request->user();
         assert($viewer !== null);
         Gate::forUser($viewer)->authorize('delete', $comment);
-        abort_unless($this->library->allowsFile($viewer, $comment->file), 403);
 
         $this->comments->remove($comment);
 
diff --git a/docs/api/openapi.json b/docs/api/openapi.json
index dd322939..0b8102c2 100644
--- a/docs/api/openapi.json
+++ b/docs/api/openapi.json
@@ -1140,26 +1140,7 @@
                         }
                     },
                     "403": {
-                        "description": "An error",
-                        "content": {
-                            "application/json": {
-                                "schema": {
-                                    "type": "object",
-                                    "properties": {
-                                        "message": {
-                                            "type": "string",
-                                            "description": "Error overview.",
-                                            "examples": [
-                                                ""
-                                            ]
-                                        }
-                                    },
-                                    "required": [
-                                        "message"
-                                    ]
-                                }
-                            }
-                        }
+                        "$ref": "#/components/responses/AuthorizationException"
                     },
                     "404": {
                         "$ref": "#/components/responses/ModelNotFoundException"
diff --git a/tests/Feature/Comments/ModerationLibraryScopeTest.php b/tests/Feature/Comments/ModerationLibraryScopeTest.php
new file mode 100644
index 00000000..73a85f00
--- /dev/null
+++ b/tests/Feature/Comments/ModerationLibraryScopeTest.php
@@ -0,0 +1,133 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Models\User;
+use App\Modules\Comments\Models\FileComment;
+use App\Modules\Files\Models\File;
+use App\Modules\Identity\Models\Role;
+use App\Modules\Identity\Models\RolePermission;
+use App\Modules\Platform\Settings\Setting;
+use App\Modules\Platform\Settings\Settings;
+use Laravel\Sanctum\Sanctum;
+
+beforeEach(function () {
+    $this->admin = User::factory()->create();
+    $this->settings = app(Settings::class);
+
+    $this->settings->set(Setting::CommentsScope, 'all');
+    $this->settings->set(Setting::CommentsAuthors, 'everyone');
+    $this->settings->set(Setting::PublicCommentsEnabled, true);
+    $this->settings->set(Setting::CommentsGuestModeration, true);
+    $this->settings->set(Setting::CommentsEditWindowMinutes, 15);
+});
+
+/**
+ * A moderator who is scoped to their own clients — the role that holds
+ * moderate_comments without holding the whole library.
+ */
+function commentModeratorScopedTo(?User $client = null): User
+{
+    $role = Role::query()->create(['name' => 'Scoped moderator', 'client_scoped' => true]);
+    RolePermission::query()->insert([
+        ['role_id' => $role->id, 'permission' => 'moderate_comments'],
+        ['role_id' => $role->id, 'permission' => 'upload'],
+    ]);
+
+    $manager = User::factory()->create(['role_id' => $role->id]);
+    $manager->assignedClients()->attach(($client ?? User::factory()->client()->create())->id);
+
+    return $manager;
+}
+
+/**
+ * A commented-on file belonging to somebody else's client.
+ *
+ * @return array{0: File, 1: FileComment}
+ */
+function strangersCommentedFile(User $uploader): array
+{
+    $stranger = User::factory()->client()->create();
+    $file = File::factory()->public()->create(['uploaded_by' => $uploader->id]);
+    shareFileWith($file, $stranger);
+
+    return [$file, FileComment::factory()->for($file)->fromGuest()->pending()->create()];
+}
+
+test('a scoped moderator cannot delete a comment on a file outside their library', function () {
+    [, $comment] = strangersCommentedFile($this->admin);
+
+    // The per-file endpoint, not the moderation screen: the policy is the
+    // whole gate here, since the route carries no permission of its own.
+    $this->actingAs(commentModeratorScopedTo())
+        ->deleteJson("/comments/{$comment->id}")
+        ->assertForbidden();
+
+    expect(FileComment::query()->whereKey($comment->id)->exists())->toBeTrue();
+});
+
+test('a scoped moderator cannot delete an out-of-library comment through the API', function () {
+    [, $comment] = strangersCommentedFile($this->admin);
+
+    Sanctum::actingAs(commentModeratorScopedTo(), ['upload']);
+
+    $this->deleteJson("/api/v1/comments/{$comment->id}")->assertForbidden();
+
+    expect(FileComment::query()->whereKey($comment->id)->exists())->toBeTrue();
+});
+
+test('a scoped moderator cannot delete an out-of-library comment from the moderation screen', function () {
+    [, $comment] = strangersCommentedFile($this->admin);
+
+    $this->actingAs(commentModeratorScopedTo())
+        ->delete("/comments/{$comment->id}/moderate")
+        ->assertForbidden();
+
+    expect(FileComment::query()->whereKey($comment->id)->exists())->toBeTrue();
+});
+
+test('a scoped moderator cannot approve an out-of-library comment through the API', function () {
+    [, $comment] = strangersCommentedFile($this->admin);
+
+    Sanctum::actingAs(commentModeratorScopedTo(), ['moderate_comments']);
+
+    $this->postJson("/api/v1/comments/{$comment->id}/approve")->assertForbidden();
+
+    expect($comment->fresh()->isPending())->toBeTrue();
+});
+
+test('a scoped moderator still moderates the files that are theirs', function () {
+    $mine = User::factory()->client()->create();
+    $file = File::factory()->public()->create(['uploaded_by' => $this->admin->id]);
+    shareFileWith($file, $mine);
+    $comment = FileComment::factory()->for($file)->fromGuest()->pending()->create();
+
+    // Same role, same permission — the only difference is that this file
+    // belongs to a client they are assigned to.
+    $this->actingAs(commentModeratorScopedTo($mine))
+        ->deleteJson("/comments/{$comment->id}")
+        ->assertOk();
+
+    expect(FileComment::query()->whereKey($comment->id)->exists())->toBeFalse();
+});
+
+test('an unscoped moderator still reaches every comment', function () {
+    [, $comment] = strangersCommentedFile($this->admin);
+
+    $this->actingAs($this->admin)->deleteJson("/comments/{$comment->id}")->assertOk();
+
+    expect(FileComment::query()->whereKey($comment->id)->exists())->toBeFalse();
+});
+
+test('the library boundary does not follow an author onto their own comment', function () {
+    $client = User::factory()->client()->create();
+    $file = File::factory()->public()->create(['uploaded_by' => $this->admin->id]);
+    shareFileWith($file, $client);
+    $comment = FileComment::factory()->for($file)->inThreadOf($client)->create(['author_id' => $client->id]);
+
+    // Deleting your own words inside the edit window is not moderation, and
+    // the boundary the moderation branch now carries must not reach it.
+    $this->actingAs($client)->deleteJson("/comments/{$comment->id}")->assertOk();
+
+    expect(FileComment::query()->whereKey($comment->id)->exists())->toBeFalse();
+});