diff --git a/.gitignore b/.gitignore
index 970182b9..58008dd4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -20,11 +20,7 @@ yarn-error.log
 /package-lock.json
 /auth.json
 /composer.lock
-/.fleet
 /.idea
-/.nova
-/.vscode
-/.zed
 /coverage-report*
 /coverage.xml
-/.claude
+/.php-cs-fixer.dist.php
diff --git a/app/Http/Controllers/Api/V1/PlatformChannelsController.php b/app/Http/Controllers/Api/V1/PlatformChannelsController.php
index a72f5ed4..443ba540 100644
--- a/app/Http/Controllers/Api/V1/PlatformChannelsController.php
+++ b/app/Http/Controllers/Api/V1/PlatformChannelsController.php
@@ -8,6 +8,7 @@
 use App\Models\PlatformAccount;
 use App\Models\PlatformChannel;
 use Exception;
+use Illuminate\Database\UniqueConstraintViolationException;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
 use Illuminate\Validation\ValidationException;
@@ -51,6 +52,11 @@ public function store(StorePlatformChannelRequest $request, CreateChannelAction
                 'Platform channel created successfully and linked to platform account!',
                 201
             );
+        } catch (UniqueConstraintViolationException $e) {
+            // The (platform_instance_id, channel_id) unique index is the last line of
+            // defence if a duplicate slips past request validation — surface it as a
+            // validation error rather than leaking the driver's SQL message in a 500.
+            return $this->sendError('A channel with this name already exists for this instance.', [], 422);
         } catch (RuntimeException $e) {
             return $this->sendError($e->getMessage(), [], 422);
         } catch (Exception $e) {
diff --git a/app/Http/Requests/StorePlatformChannelRequest.php b/app/Http/Requests/StorePlatformChannelRequest.php
index 0950699f..0a1af8c6 100644
--- a/app/Http/Requests/StorePlatformChannelRequest.php
+++ b/app/Http/Requests/StorePlatformChannelRequest.php
@@ -3,6 +3,7 @@
 namespace App\Http\Requests;
 
 use Illuminate\Foundation\Http\FormRequest;
+use Illuminate\Validation\Rule;
 
 class StorePlatformChannelRequest extends FormRequest
 {
@@ -12,15 +13,36 @@ public function authorize(): bool
     }
 
     /**
-     * @return array<string, string>
+     * @return array<string, array<int, mixed>|string>
      */
     public function rules(): array
     {
         return [
             'platform_instance_id' => 'required|exists:platform_instances,id',
-            'name' => 'required|string|max:255',
+            // name doubles as the Lemmy community slug (CreateChannelAction copies it
+            // verbatim into channel_id for community lookup at publish time), so it must
+            // be slug format and unique per instance — matching the Livewire create form.
+            'name' => [
+                'required',
+                'string',
+                'max:255',
+                'regex:/^[a-z0-9_]+$/',
+                Rule::unique('platform_channels', 'name')
+                    ->where('platform_instance_id', $this->input('platform_instance_id')),
+            ],
             'language_id' => 'nullable|exists:languages,id',
             'description' => 'nullable|string',
         ];
     }
+
+    /**
+     * @return array<string, string>
+     */
+    public function messages(): array
+    {
+        return [
+            'name.regex' => 'The name must be a valid community slug (lowercase letters, numbers, and underscores only).',
+            'name.unique' => 'A channel with this name already exists for this instance.',
+        ];
+    }
 }
diff --git a/app/Jobs/SyncChannelPostsJob.php b/app/Jobs/SyncChannelPostsJob.php
index 3ded0649..edf86824 100644
--- a/app/Jobs/SyncChannelPostsJob.php
+++ b/app/Jobs/SyncChannelPostsJob.php
@@ -65,17 +65,19 @@ private function syncLemmyChannelPosts(LogSaver $logSaver): void
                 throw new PlatformAuthException(PlatformEnum::LEMMY, 'No active account found for channel');
             }
 
-            $api = new LemmyApiService($this->channel->platformInstance->url);
+            $api = $this->makeApiService($this->channel->platformInstance->url);
             $token = $this->getAuthToken($api, $account);
 
-            $platformChannelId = $this->channel->channel_id
-                ? $this->channel->channel_id
-                : $api->getCommunityId($this->channel->name, $token);
+            // channel_id holds a Lemmy community slug (non-numeric) or a numeric
+            // community id; syncChannelPosts() needs the numeric id. Mirror the
+            // resolution used in LemmyPublisher::createPost().
+            $communityId = is_numeric($this->channel->channel_id)
+                ? (int) $this->channel->channel_id
+                : $api->getCommunityId($this->channel->channel_id, $token);
 
-            $api->syncChannelPosts($token, $platformChannelId, $this->channel->name);
+            $api->syncChannelPosts($token, $communityId, $this->channel->name);
 
             $logSaver->info('Channel posts synced successfully', $this->channel);
-
         } catch (Exception $e) {
             $logSaver->error('Failed to sync channel posts', $this->channel, [
                 'error' => $e->getMessage(),
@@ -85,6 +87,15 @@ private function syncLemmyChannelPosts(LogSaver $logSaver): void
         }
     }
 
+    /**
+     * Seam for testing — LemmyApiService needs a per-instance URL so it cannot be
+     * container-resolved. Override in tests to inject a mock.
+     */
+    protected function makeApiService(string $instanceUrl): LemmyApiService
+    {
+        return new LemmyApiService($instanceUrl);
+    }
+
     /**
      * @throws PlatformAuthException
      */
diff --git a/app/Livewire/Channels.php b/app/Livewire/Channels.php
index 2dab6276..0b785186 100644
--- a/app/Livewire/Channels.php
+++ b/app/Livewire/Channels.php
@@ -8,6 +8,7 @@
 use App\Models\PlatformChannel;
 use App\Models\PlatformInstance;
 use Illuminate\Contracts\View\View;
+use Illuminate\Database\UniqueConstraintViolationException;
 use Illuminate\Validation\Rule;
 use Livewire\Component;
 use RuntimeException;
@@ -73,6 +74,13 @@ public function createChannel(CreateChannelAction $action): void
                 // Blade textarea binds an empty string when blank; the action expects null for "no description".
                 $this->newDescription !== '' ? $this->newDescription : null,
             );
+        } catch (UniqueConstraintViolationException $e) {
+            // Unreachable via this form (the unique rule above catches duplicates first),
+            // but the (platform_instance_id, channel_id) index can still fire if channel_id
+            // ever drifts from name. Surface it as a field error instead of a 500.
+            $this->addError('newName', 'A channel with this name already exists for this instance.');
+
+            return;
         } catch (RuntimeException $e) {
             $this->addError('newPlatformInstanceId', $e->getMessage());
 
diff --git a/app/Models/PlatformChannel.php b/app/Models/PlatformChannel.php
index 9291a36e..055b5f60 100644
--- a/app/Models/PlatformChannel.php
+++ b/app/Models/PlatformChannel.php
@@ -15,7 +15,7 @@
  * @property int $id
  * @property int $platform_instance_id
  * @property PlatformInstance $platformInstance
- * @property int $channel_id
+ * @property string $channel_id
  * @property string $name
  * @property int $language_id
  * @property Language|null $language
diff --git a/database/migrations/2024_01_01_000011_add_channel_id_unique_to_platform_channels.php b/database/migrations/2024_01_01_000011_add_channel_id_unique_to_platform_channels.php
new file mode 100644
index 00000000..952f9b64
--- /dev/null
+++ b/database/migrations/2024_01_01_000011_add_channel_id_unique_to_platform_channels.php
@@ -0,0 +1,57 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * channel_id is used verbatim as the Lemmy community slug at publish time
+     * (LemmyPublisher -> getCommunityId). It is kept equal to `name` on create,
+     * but only `name` had a uniqueness guarantee. Enforce the same scope on
+     * channel_id so duplicate/ambiguous community references cannot exist.
+     */
+    public function up(): void
+    {
+        $this->guardAgainstDuplicates();
+
+        Schema::table('platform_channels', function (Blueprint $table) {
+            $table->unique(['platform_instance_id', 'channel_id'], 'platform_channels_channel_id_unique');
+        });
+    }
+
+    /**
+     * Pre-flight check so an existing database with drifted data fails with an
+     * actionable message naming the offending rows, rather than a raw driver error.
+     */
+    private function guardAgainstDuplicates(): void
+    {
+        $duplicates = DB::table('platform_channels')
+            ->select('platform_instance_id', 'channel_id', DB::raw('COUNT(*) as total'))
+            ->groupBy('platform_instance_id', 'channel_id')
+            ->havingRaw('COUNT(*) > 1')
+            ->get();
+
+        if ($duplicates->isEmpty()) {
+            return;
+        }
+
+        $details = $duplicates
+            ->map(fn ($row) => "platform_instance_id={$row->platform_instance_id} channel_id='{$row->channel_id}' ({$row->total} rows)")
+            ->implode('; ');
+
+        throw new RuntimeException(
+            'Cannot add unique index on platform_channels (platform_instance_id, channel_id): '.
+            'duplicate rows exist. Resolve these before migrating: '.$details
+        );
+    }
+
+    public function down(): void
+    {
+        Schema::table('platform_channels', function (Blueprint $table) {
+            $table->dropUnique('platform_channels_channel_id_unique');
+        });
+    }
+};
diff --git a/tests/Feature/Http/Controllers/Api/V1/PlatformChannelsControllerTest.php b/tests/Feature/Http/Controllers/Api/V1/PlatformChannelsControllerTest.php
index 84f06cbe..9ad57d9e 100644
--- a/tests/Feature/Http/Controllers/Api/V1/PlatformChannelsControllerTest.php
+++ b/tests/Feature/Http/Controllers/Api/V1/PlatformChannelsControllerTest.php
@@ -111,6 +111,69 @@ public function test_store_validates_platform_instance_exists(): void
             ->assertJsonValidationErrors(['platform_instance_id']);
     }
 
+    public function test_store_rejects_non_slug_name(): void
+    {
+        $instance = PlatformInstance::factory()->create();
+
+        // name is copied verbatim into channel_id and used as the Lemmy community
+        // reference, so non-slug values must be rejected at the API boundary too.
+        $response = $this->postJson('/api/v1/platform-channels', [
+            'platform_instance_id' => $instance->id,
+            'name' => 'Tech News',
+        ]);
+
+        $response->assertStatus(422)
+            ->assertJsonValidationErrors(['name']);
+
+        $this->assertDatabaseCount('platform_channels', 0);
+    }
+
+    public function test_store_rejects_duplicate_name_for_same_instance(): void
+    {
+        $instance = PlatformInstance::factory()->create();
+        PlatformChannel::factory()->create([
+            'platform_instance_id' => $instance->id,
+            'name' => 'tech_news',
+            'channel_id' => 'tech_news',
+        ]);
+
+        $response = $this->postJson('/api/v1/platform-channels', [
+            'platform_instance_id' => $instance->id,
+            'name' => 'tech_news',
+        ]);
+
+        $response->assertStatus(422)
+            ->assertJsonValidationErrors(['name']);
+
+        $this->assertDatabaseCount('platform_channels', 1);
+    }
+
+    public function test_store_allows_same_name_on_different_instance(): void
+    {
+        $instanceA = PlatformInstance::factory()->create();
+        $instanceB = PlatformInstance::factory()->create();
+
+        PlatformAccount::factory()->create([
+            'instance_url' => $instanceB->url,
+            'is_active' => true,
+        ]);
+
+        PlatformChannel::factory()->create([
+            'platform_instance_id' => $instanceA->id,
+            'name' => 'tech_news',
+            'channel_id' => 'tech_news',
+        ]);
+
+        $response = $this->postJson('/api/v1/platform-channels', [
+            'platform_instance_id' => $instanceB->id,
+            'name' => 'tech_news',
+        ]);
+
+        $response->assertStatus(201);
+
+        $this->assertDatabaseCount('platform_channels', 2);
+    }
+
     public function test_show_returns_platform_channel_successfully(): void
     {
         $instance = PlatformInstance::factory()->create();
diff --git a/tests/Unit/Jobs/SyncChannelPostsJobTest.php b/tests/Unit/Jobs/SyncChannelPostsJobTest.php
index d439bff1..db31c90a 100644
--- a/tests/Unit/Jobs/SyncChannelPostsJobTest.php
+++ b/tests/Unit/Jobs/SyncChannelPostsJobTest.php
@@ -7,6 +7,7 @@
 use App\Models\PlatformAccount;
 use App\Models\PlatformChannel;
 use App\Models\PlatformInstance;
+use App\Modules\Lemmy\Services\LemmyApiService;
 use App\Services\Log\LogSaver;
 use Exception;
 use Illuminate\Contracts\Queue\ShouldBeUnique;
@@ -132,6 +133,110 @@ public function test_handle_logs_start_message(): void
         $this->assertTrue(true);
     }
 
+    public function test_sync_resolves_non_numeric_channel_id_via_get_community_id(): void
+    {
+        [$channel, $account] = $this->makeSyncableChannel('tech_news');
+
+        $apiMock = Mockery::mock(LemmyApiService::class);
+        $apiMock->shouldReceive('login')
+            ->once()
+            ->with($account->username, $account->password)
+            ->andReturn('token');
+        $apiMock->shouldReceive('getCommunityId')
+            ->once()
+            ->with('tech_news', 'token')
+            ->andReturn(42);
+        $apiMock->shouldReceive('syncChannelPosts')
+            ->once()
+            ->with('token', 42, $channel->name);
+
+        $logSaverMock = Mockery::mock(LogSaver::class);
+        $logSaverMock->shouldReceive('info')->zeroOrMoreTimes();
+        $logSaverMock->shouldReceive('error')->zeroOrMoreTimes();
+
+        $this->makeJobWithApi($channel, $apiMock)->handle($logSaverMock);
+
+        // The behaviour under test is the mocked call sequence above; assert explicitly
+        // so PHPUnit does not flag the test as risky for performing no assertions.
+        $this->addToAssertionCount(1);
+    }
+
+    public function test_sync_uses_numeric_channel_id_directly_without_lookup(): void
+    {
+        [$channel, $account] = $this->makeSyncableChannel('42');
+
+        $apiMock = Mockery::mock(LemmyApiService::class);
+        $apiMock->shouldReceive('login')
+            ->once()
+            ->with($account->username, $account->password)
+            ->andReturn('token');
+        // The behaviour that matters here is that no community lookup happens — the
+        // numeric channel_id is used as-is. (The int-ness of the argument is not worth
+        // asserting: syncChannelPosts() declares `int $platformChannelId`, so PHP coerces
+        // '42' at the call boundary whether or not the job casts it first.)
+        $apiMock->shouldNotReceive('getCommunityId');
+        $apiMock->shouldReceive('syncChannelPosts')
+            ->once()
+            ->with('token', 42, $channel->name);
+
+        $logSaverMock = Mockery::mock(LogSaver::class);
+        $logSaverMock->shouldReceive('info')->zeroOrMoreTimes();
+        $logSaverMock->shouldReceive('error')->zeroOrMoreTimes();
+
+        $this->makeJobWithApi($channel, $apiMock)->handle($logSaverMock);
+
+        // As above: the shouldNotReceive('getCommunityId') expectation is the assertion.
+        $this->addToAssertionCount(1);
+    }
+
+    /**
+     * @return array{0: PlatformChannel, 1: PlatformAccount}
+     */
+    private function makeSyncableChannel(string $channelId): array
+    {
+        $platformInstance = PlatformInstance::factory()->create([
+            'platform' => PlatformEnum::LEMMY,
+            'url' => 'https://lemmy.example.com',
+        ]);
+
+        $account = PlatformAccount::factory()->create([
+            'instance_url' => $platformInstance->url,
+            'is_active' => true,
+        ]);
+
+        $channel = PlatformChannel::factory()->create([
+            'platform_instance_id' => $platformInstance->id,
+            'name' => 'tech_news',
+            'channel_id' => $channelId,
+            'is_active' => true,
+        ]);
+
+        $channel->platformAccounts()->attach($account->id, [
+            'is_active' => true,
+            'priority' => 1,
+            'created_at' => now(),
+            'updated_at' => now(),
+        ]);
+
+        return [$channel->fresh(['platformInstance']), $account];
+    }
+
+    private function makeJobWithApi(PlatformChannel $channel, LemmyApiService $api): SyncChannelPostsJob
+    {
+        return new class($channel, $api) extends SyncChannelPostsJob
+        {
+            public function __construct(PlatformChannel $channel, private readonly LemmyApiService $api)
+            {
+                parent::__construct($channel);
+            }
+
+            protected function makeApiService(string $instanceUrl): LemmyApiService
+            {
+                return $this->api;
+            }
+        };
+    }
+
     public function test_job_can_be_serialized(): void
     {
         $platformInstance = PlatformInstance::factory()->create();
diff --git a/tests/Unit/Models/PlatformChannelTest.php b/tests/Unit/Models/PlatformChannelTest.php
index f6e81bab..6e6bfeb4 100644
--- a/tests/Unit/Models/PlatformChannelTest.php
+++ b/tests/Unit/Models/PlatformChannelTest.php
@@ -9,6 +9,7 @@
 use App\Models\PlatformInstance;
 use App\Models\Route;
 use Carbon\Carbon;
+use Illuminate\Database\UniqueConstraintViolationException;
 use Illuminate\Foundation\Testing\RefreshDatabase;
 use Tests\TestCase;
 
@@ -45,6 +46,42 @@ public function test_casts_is_active_to_boolean(): void
         $this->assertFalse($channel->is_active);
     }
 
+    public function test_channel_id_is_unique_per_platform_instance(): void
+    {
+        $instance = PlatformInstance::factory()->create();
+        PlatformChannel::factory()->create([
+            'platform_instance_id' => $instance->id,
+            'name' => 'tech',
+            'channel_id' => 'tech',
+        ]);
+
+        $this->expectException(UniqueConstraintViolationException::class);
+
+        PlatformChannel::factory()->create([
+            'platform_instance_id' => $instance->id,
+            'name' => 'tech_alias',
+            'channel_id' => 'tech',
+        ]);
+    }
+
+    public function test_same_channel_id_allowed_across_different_instances(): void
+    {
+        $instanceA = PlatformInstance::factory()->create();
+        $instanceB = PlatformInstance::factory()->create();
+
+        PlatformChannel::factory()->create([
+            'platform_instance_id' => $instanceA->id,
+            'channel_id' => 'tech',
+        ]);
+        $second = PlatformChannel::factory()->create([
+            'platform_instance_id' => $instanceB->id,
+            'channel_id' => 'tech',
+        ]);
+
+        $this->assertDatabaseCount('platform_channels', 2);
+        $this->assertEquals('tech', $second->channel_id);
+    }
+
     public function test_belongs_to_platform_instance_relationship(): void
     {
         $instance = PlatformInstance::factory()->create();