diff --git a/app/Modules/Comments/FileComments.php b/app/Modules/Comments/FileComments.php
index c61672b2..5bd66da0 100644
--- a/app/Modules/Comments/FileComments.php
+++ b/app/Modules/Comments/FileComments.php
@@ -220,10 +220,27 @@ class FileComments
             return null;
         }
 
+        // Asked of the column, not of the relation. client_context_id is
+        // cascadeOnDelete, but a user is soft-deleted, so the cascade
+        // never fires: the column goes on pointing at a row that is still
+        // there while the relation resolves to null. Branching on the
+        // relation therefore read "this is Alice's conversation" as "this
+        // has no conversation" — and a null context on a Clients comment
+        // is the branch every client on the file reads (see
+        // VisibleCommentScope's opening rule). A private reply became a
+        // circular, and canAssignClient below was skipped on the way.
+        if ($replyTo->client_context_id === null) {
+            return null;
+        }
+
         $client = $replyTo->clientContext;
 
         if ($client === null) {
-            return null;
+            // The column points at somebody, and that somebody is gone.
+            // There is nobody to answer, and the one outcome that must
+            // not follow from a filled column is the broadcast above, so
+            // this refuses rather than falling through to it.
+            throw new AuthorizationException('You cannot reply in this conversation.');
         }
 
         if (! $this->library->canAssignClient($author, $client)) {
diff --git a/app/Modules/Comments/Models/FileComment.php b/app/Modules/Comments/Models/FileComment.php
index 7cdd80a9..2be4cd19 100644
--- a/app/Modules/Comments/Models/FileComment.php
+++ b/app/Modules/Comments/Models/FileComment.php
@@ -113,18 +113,32 @@ class FileComment extends Model
      * The name to show. Snapshotted for guests at write time; read live
      * for accounts so a rename is reflected everywhere at once.
      *
-     * author_id cascades on delete, so a row that has one always has the
-     * account behind it — there is no deleted-author case to snapshot
-     * against, unlike the activity log's actor_name.
+     * A deleted account is still read. author_id cascades on delete, but
+     * a user is soft-deleted and the cascade never fires, so the row
+     * behind a deleted commenter is still there — and reading it through
+     * the plain relation returned null, which sent a named client's
+     * comment out as "Anonymous". That is what a guest comment looks
+     * like, and a guest comment is governed by different rules; the two
+     * must not be able to look the same. Whether the author is a guest is
+     * decided by author_id alone, which is also what isFromGuest() asks.
      */
     public function authorName(): string
     {
+        if ($this->author_id === null) {
+            return $this->guest_name ?? (string) __('Anonymous');
+        }
+
         $author = $this->author;
 
         if ($author !== null) {
             return $author->name;
         }
 
-        return $this->guest_name ?? (string) __('Anonymous');
+        // Trashed: the row is still there, the relation simply will not
+        // hand it over. Nothing comes back only once the grace-period
+        // erasure has removed the row for real.
+        $name = $this->author()->withTrashed()->value('name');
+
+        return is_string($name) ? $name : (string) __('Anonymous');
     }
 }
diff --git a/tests/Feature/Comments/DeletedClientThreadTest.php b/tests/Feature/Comments/DeletedClientThreadTest.php
new file mode 100644
index 00000000..8bacd09a
--- /dev/null
+++ b/tests/Feature/Comments/DeletedClientThreadTest.php
@@ -0,0 +1,100 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Models\User;
+use App\Modules\Comments\Access\VisibleCommentScope;
+use App\Modules\Comments\CommentVisibility;
+use App\Modules\Comments\Models\FileComment;
+use App\Modules\Files\Models\File;
+use Illuminate\Support\Facades\Storage;
+
+/**
+ * `file_comments.client_context_id` and `author_id` are both
+ * cascadeOnDelete, and neither cascade ever fires: users are
+ * soft-deleted, so the row survives and the column goes on pointing at
+ * it. Everything that asked the *relation* instead of the column read
+ * that as "there is no client here" — and for client_context_id, "no
+ * client" is the branch every client on the file reads.
+ */
+beforeEach(function () {
+    Storage::fake('files');
+    $this->admin = User::factory()->create();
+    $this->file = File::factory()->create(['name' => 'Quote']);
+    $this->alice = User::factory()->client()->create(['name' => 'Alice Ltd']);
+    $this->bob = User::factory()->client()->create(['name' => 'Bob GmbH']);
+
+    shareFileWith($this->file, $this->alice);
+    shareFileWith($this->file, $this->bob);
+
+    $this->fromAlice = FileComment::factory()->for($this->file)->inThreadOf($this->alice)->create([
+        'author_id' => $this->alice->id,
+        'body' => 'What is your best price?',
+    ]);
+});
+
+function readableBy(User $viewer, File $file): array
+{
+    return app(VisibleCommentScope::class)->for($viewer, $file)->pluck('id')->map(intval(...))->all();
+}
+
+test('a reply into a deleted client\'s thread is refused, not broadcast', function () {
+    $this->alice->delete();
+
+    $this->actingAs($this->admin)
+        ->postJson("/files/{$this->file->id}/comments", [
+            'body' => 'For you only: 40% off.',
+            'visibility' => CommentVisibility::Clients->value,
+            'reply_to' => $this->fromAlice->id,
+        ])
+        ->assertForbidden();
+
+    expect(FileComment::query()->where('body', 'For you only: 40% off.')->exists())->toBeFalse()
+        ->and(readableBy($this->bob, $this->file))->toBe([]);
+});
+
+test('a staff message to everybody still reaches everybody', function () {
+    // The null context is a real branch, not only a failure mode: staff
+    // writing fresh address every client on the file, and that must keep
+    // working.
+    $this->actingAs($this->admin)
+        ->postJson("/files/{$this->file->id}/comments", [
+            'body' => 'The catalogue is attached.',
+            'visibility' => CommentVisibility::Clients->value,
+        ])
+        ->assertCreated();
+
+    $broadcast = FileComment::query()->where('body', 'The catalogue is attached.')->sole();
+
+    expect($broadcast->client_context_id)->toBeNull()
+        ->and(readableBy($this->bob, $this->file))->toContain($broadcast->id);
+});
+
+test('a reply into a live client\'s thread still lands in that thread alone', function () {
+    $this->actingAs($this->admin)
+        ->postJson("/files/{$this->file->id}/comments", [
+            'body' => 'For you only: 40% off.',
+            'visibility' => CommentVisibility::Clients->value,
+            'reply_to' => $this->fromAlice->id,
+        ])
+        ->assertCreated();
+
+    $reply = FileComment::query()->where('body', 'For you only: 40% off.')->sole();
+
+    expect($reply->client_context_id)->toBe($this->alice->id)
+        ->and(readableBy($this->alice, $this->file))->toContain($reply->id)
+        ->and(readableBy($this->bob, $this->file))->not->toContain($reply->id);
+});
+
+test('a deleted client\'s comment keeps their name instead of reading as a guest', function () {
+    $this->alice->delete();
+
+    expect($this->fromAlice->fresh()->authorName())->toBe('Alice Ltd');
+});
+
+test('a genuine guest comment is still anonymous', function () {
+    $guest = FileComment::factory()->for($this->file)->fromGuest()->create();
+
+    expect($guest->authorName())->not->toBe('Alice Ltd')
+        ->and($guest->author_id)->toBeNull();
+});