diff --git a/app/Filament/System/Pages/Auth/Login.php b/app/Filament/System/Pages/Auth/Login.php
index e4c2c31..333cd25 100644
--- a/app/Filament/System/Pages/Auth/Login.php
+++ b/app/Filament/System/Pages/Auth/Login.php
@@ -9,6 +9,7 @@
 use App\Services\Intune\AuditLogger;
 use Filament\Auth\Http\Responses\Contracts\LoginResponse;
 use Filament\Auth\Pages\Login as BaseLogin;
+use Illuminate\Support\Facades\RateLimiter;
 use Illuminate\Validation\ValidationException;
 
 class Login extends BaseLogin
@@ -17,10 +18,25 @@ public function authenticate(): ?LoginResponse
     {
         $data = $this->form->getState();
         $email = (string) ($data['email'] ?? '');
+        $throttleKey = $this->throttleKey($email);
+
+        if (RateLimiter::tooManyAttempts($throttleKey, 10)) {
+            $this->audit(status: 'failure', email: $email, actor: null, reason: 'throttled');
+
+            $seconds = RateLimiter::availableIn($throttleKey);
+
+            throw ValidationException::withMessages([
+                'data.email' => __('auth.throttle', [
+                    'seconds' => $seconds,
+                    'minutes' => (int) ceil($seconds / 60),
+                ]),
+            ]);
+        }
 
         try {
             $response = parent::authenticate();
         } catch (ValidationException $exception) {
+            RateLimiter::hit($throttleKey, 60);
             $this->audit(status: 'failure', email: $email, actor: null, reason: 'invalid_credentials');
 
             throw $exception;
@@ -40,6 +56,7 @@ public function authenticate(): ?LoginResponse
         if (! $user->is_active) {
             auth('platform')->logout();
 
+            RateLimiter::hit($throttleKey, 60);
             $this->audit(status: 'failure', email: $email, actor: null, reason: 'inactive');
 
             throw ValidationException::withMessages([
@@ -47,6 +64,7 @@ public function authenticate(): ?LoginResponse
             ]);
         }
 
+        RateLimiter::clear($throttleKey);
         $user->forceFill(['last_login_at' => now()])->saveQuietly();
 
         $this->audit(status: 'success', email: $email, actor: $user);
@@ -54,6 +72,14 @@ public function authenticate(): ?LoginResponse
         return $response;
     }
 
+    private function throttleKey(string $email): string
+    {
+        $ip = (string) request()->ip();
+        $normalizedEmail = mb_strtolower(trim($email));
+
+        return "system-login:{$ip}:{$normalizedEmail}";
+    }
+
     private function audit(string $status, string $email, ?PlatformUser $actor, ?string $reason = null): void
     {
         $tenant = Tenant::query()->where('external_id', 'platform')->first();
diff --git a/app/Http/Middleware/EnsurePlatformCapability.php b/app/Http/Middleware/EnsurePlatformCapability.php
index 29efd6f..0547fba 100644
--- a/app/Http/Middleware/EnsurePlatformCapability.php
+++ b/app/Http/Middleware/EnsurePlatformCapability.php
@@ -29,7 +29,7 @@ public function handle(Request $request, Closure $next, string $capability): Res
         }
 
         if (! Gate::forUser($user)->allows($capability)) {
-            abort(404);
+            abort(403);
         }
 
         return $next($request);
diff --git a/app/Http/Middleware/UseSystemSessionCookie.php b/app/Http/Middleware/UseSystemSessionCookie.php
new file mode 100644
index 0000000..7d328c3
--- /dev/null
+++ b/app/Http/Middleware/UseSystemSessionCookie.php
@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Illuminate\Support\Str;
+use Symfony\Component\HttpFoundation\Response;
+
+class UseSystemSessionCookie
+{
+    /**
+     * @param  \Closure(\Illuminate\Http\Request): (\Symfony\Component\HttpFoundation\Response)  $next
+     */
+    public function handle(Request $request, Closure $next): Response
+    {
+        $originalCookieName = (string) config('session.cookie');
+
+        config(['session.cookie' => $this->systemCookieName()]);
+
+        try {
+            return $next($request);
+        } finally {
+            config(['session.cookie' => $originalCookieName]);
+        }
+    }
+
+    private function systemCookieName(): string
+    {
+        return Str::slug((string) config('app.name', 'laravel')).'-system-session';
+    }
+}
+
diff --git a/app/Providers/Filament/SystemPanelProvider.php b/app/Providers/Filament/SystemPanelProvider.php
index 98a42bc..27a4997 100644
--- a/app/Providers/Filament/SystemPanelProvider.php
+++ b/app/Providers/Filament/SystemPanelProvider.php
@@ -2,8 +2,10 @@
 
 namespace App\Providers\Filament;
 
+use App\Http\Middleware\UseSystemSessionCookie;
 use App\Filament\System\Pages\Auth\Login;
 use App\Filament\System\Pages\Dashboard;
+use App\Support\Auth\PlatformCapabilities;
 use Filament\Http\Middleware\Authenticate;
 use Filament\Http\Middleware\AuthenticateSession;
 use Filament\Http\Middleware\DisableBladeIconComponents;
@@ -42,6 +44,7 @@ public function panel(Panel $panel): Panel
             ->middleware([
                 EncryptCookies::class,
                 AddQueuedCookiesToResponse::class,
+                UseSystemSessionCookie::class,
                 StartSession::class,
                 AuthenticateSession::class,
                 ShareErrorsFromSession::class,
@@ -53,7 +56,7 @@ public function panel(Panel $panel): Panel
             ])
             ->authMiddleware([
                 Authenticate::class,
-                'ensure-platform-capability:platform.access_system_panel',
+                'ensure-platform-capability:'.PlatformCapabilities::ACCESS_SYSTEM_PANEL,
             ]);
     }
 }
diff --git a/app/Services/System/AllowedTenantUniverse.php b/app/Services/System/AllowedTenantUniverse.php
new file mode 100644
index 0000000..2758a6b
--- /dev/null
+++ b/app/Services/System/AllowedTenantUniverse.php
@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Services\System;
+
+use App\Models\Tenant;
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Validation\ValidationException;
+
+class AllowedTenantUniverse
+{
+    public const PLATFORM_TENANT_EXTERNAL_ID = 'platform';
+
+    public function query(): Builder
+    {
+        return Tenant::query()
+            ->where('external_id', '!=', self::PLATFORM_TENANT_EXTERNAL_ID);
+    }
+
+    public function isAllowed(Tenant $tenant): bool
+    {
+        return (string) $tenant->external_id !== self::PLATFORM_TENANT_EXTERNAL_ID;
+    }
+
+    public function ensureAllowed(Tenant $tenant): void
+    {
+        if ($this->isAllowed($tenant)) {
+            return;
+        }
+
+        throw ValidationException::withMessages([
+            'tenant_id' => 'This tenant is not eligible for System runbooks.',
+        ]);
+    }
+}
+
diff --git a/app/Support/Auth/PlatformCapabilities.php b/app/Support/Auth/PlatformCapabilities.php
index f409c1d..3e032c5 100644
--- a/app/Support/Auth/PlatformCapabilities.php
+++ b/app/Support/Auth/PlatformCapabilities.php
@@ -14,6 +14,14 @@ class PlatformCapabilities
 
     public const USE_BREAK_GLASS = 'platform.use_break_glass';
 
+    public const OPS_VIEW = 'platform.ops.view';
+
+    public const RUNBOOKS_VIEW = 'platform.runbooks.view';
+
+    public const RUNBOOKS_RUN = 'platform.runbooks.run';
+
+    public const RUNBOOKS_FINDINGS_LIFECYCLE_BACKFILL = 'platform.runbooks.findings.lifecycle_backfill';
+
     /**
      * @return array<string>
      */
diff --git a/specs/113-platform-ops-runbooks/tasks.md b/specs/113-platform-ops-runbooks/tasks.md
index 544f045..aa5235d 100644
--- a/specs/113-platform-ops-runbooks/tasks.md
+++ b/specs/113-platform-ops-runbooks/tasks.md
@@ -16,10 +16,10 @@ ## Phase 1: Setup (Shared Infrastructure)
 
 **Purpose**: Confirm touch points and keep spec artifacts aligned.
 
-- [ ] T001 Confirm spec UI Action Matrix is complete in specs/113-platform-ops-runbooks/spec.md
-- [ ] T002 Confirm System panel provider registration in bootstrap/providers.php (Laravel 11+/12 provider registration)
-- [ ] T003 [P] Capture current legacy /admin trigger location in app/Filament/Resources/FindingResource/Pages/ListFindings.php ("Backfill findings lifecycle" header action)
-- [ ] T004 [P] Review existing single-tenant backfill pipeline entry points in app/Console/Commands/TenantpilotBackfillFindingLifecycle.php and app/Jobs/BackfillFindingLifecycleJob.php
+- [X] T001 Confirm spec UI Action Matrix is complete in specs/113-platform-ops-runbooks/spec.md
+- [X] T002 Confirm System panel provider registration in bootstrap/providers.php (Laravel 11+/12 provider registration)
+- [X] T003 [P] Capture current legacy /admin trigger location in app/Filament/Resources/FindingResource/Pages/ListFindings.php ("Backfill findings lifecycle" header action)
+- [X] T004 [P] Review existing single-tenant backfill pipeline entry points in app/Console/Commands/TenantpilotBackfillFindingLifecycle.php and app/Jobs/BackfillFindingLifecycleJob.php
 
 ---
 
@@ -27,20 +27,20 @@ ## Phase 2: Foundational (Blocking Prerequisites)
 
 **Purpose**: Security semantics, session isolation, and auth hardening that block all user stories.
 
-- [ ] T005 Add platform runbook capability constants to app/Support/Auth/PlatformCapabilities.php (e.g., platform.ops.view, platform.runbooks.view, platform.runbooks.run, platform.runbooks.findings.lifecycle_backfill)
-- [ ] T006 Update System panel access control to use capability registry constants in app/Providers/Filament/SystemPanelProvider.php (keep ACCESS_SYSTEM_PANEL gate, add per-page capability checks)
-- [ ] T007 Change platform capability denial semantics to 403 (member-but-missing-capability) in app/Http/Middleware/EnsurePlatformCapability.php (keep wrong-plane 404 handled by ensure-correct-guard)
-- [ ] T008 [P] Add SR-002 regression tests for 404 vs 403 semantics in tests/Feature/System/Spec113/AuthorizationSemanticsTest.php (tenant user -> 404 on /system/*, platform user without capability -> 403, platform user with capability -> 200)
+- [X] T005 Add platform runbook capability constants to app/Support/Auth/PlatformCapabilities.php (e.g., platform.ops.view, platform.runbooks.view, platform.runbooks.run, platform.runbooks.findings.lifecycle_backfill)
+- [X] T006 Update System panel access control to use capability registry constants in app/Providers/Filament/SystemPanelProvider.php (keep ACCESS_SYSTEM_PANEL gate, add per-page capability checks)
+- [X] T007 Change platform capability denial semantics to 403 (member-but-missing-capability) in app/Http/Middleware/EnsurePlatformCapability.php (keep wrong-plane 404 handled by ensure-correct-guard)
+- [X] T008 [P] Add SR-002 regression tests for 404 vs 403 semantics in tests/Feature/System/Spec113/AuthorizationSemanticsTest.php (tenant user -> 404 on /system/*, platform user without capability -> 403, platform user with capability -> 200)
 
-- [ ] T009 Define and enforce the “allowed tenant universe” for System runbooks in app/Services/System/AllowedTenantUniverse.php (v1: exclude platform tenant; provide tenant query for pickers and runtime guard)
-- [ ] T010 [P] Add allowed tenant universe tests in tests/Feature/System/Spec113/AllowedTenantUniverseTest.php (picker excludes platform tenant; attempts to target excluded tenant are rejected; no OperationRun created)
+- [X] T009 Define and enforce the “allowed tenant universe” for System runbooks in app/Services/System/AllowedTenantUniverse.php (v1: exclude platform tenant; provide tenant query for pickers and runtime guard)
+- [X] T010 [P] Add allowed tenant universe tests in tests/Feature/System/Spec113/AllowedTenantUniverseTest.php (picker excludes platform tenant; attempts to target excluded tenant are rejected; no OperationRun created)
 
-- [ ] T011 Create System session cookie isolation middleware in app/Http/Middleware/UseSystemSessionCookie.php (set dedicated session cookie name before StartSession)
-- [ ] T012 Wire System session cookie middleware before StartSession in app/Providers/Filament/SystemPanelProvider.php (SR-004)
-- [ ] T013 [P] Add System session isolation test in tests/Feature/System/Spec113/SystemSessionIsolationTest.php (assert response sets the System session cookie name for /system)
+- [X] T011 Create System session cookie isolation middleware in app/Http/Middleware/UseSystemSessionCookie.php (set dedicated session cookie name before StartSession)
+- [X] T012 Wire System session cookie middleware before StartSession in app/Providers/Filament/SystemPanelProvider.php (SR-004)
+- [X] T013 [P] Add System session isolation test in tests/Feature/System/Spec113/SystemSessionIsolationTest.php (assert response sets the System session cookie name for /system)
 
-- [ ] T014 Implement /system/login throttling (10/min per IP + username key) in app/Filament/System/Pages/Auth/Login.php (SR-003; use RateLimiter and clear on success)
-- [ ] T015 [P] Add /system/login throttling tests in tests/Feature/System/Spec113/SystemLoginThrottleTest.php (assert throttled after N failures; ensure failures still emit audit via AuditLogger)
+- [X] T014 Implement /system/login throttling (10/min per IP + username key) in app/Filament/System/Pages/Auth/Login.php (SR-003; use RateLimiter and clear on success)
+- [X] T015 [P] Add /system/login throttling tests in tests/Feature/System/Spec113/SystemLoginThrottleTest.php (assert throttled after N failures; ensure failures still emit audit via AuditLogger)
 
 ---
 
diff --git a/tests/Feature/Auth/SystemPanelAuthTest.php b/tests/Feature/Auth/SystemPanelAuthTest.php
index 155220a..754d3d6 100644
--- a/tests/Feature/Auth/SystemPanelAuthTest.php
+++ b/tests/Feature/Auth/SystemPanelAuthTest.php
@@ -120,7 +120,7 @@
     expect($audit->metadata['reason'] ?? null)->toBe('inactive');
 });
 
-it('denies system panel access (404) for platform users without the required capability', function () {
+it('denies system panel access (403) for platform users without the required capability', function () {
     Tenant::factory()->create([
         'tenant_id' => null,
         'external_id' => 'platform',
@@ -139,7 +139,7 @@
 
     expect(auth('platform')->check())->toBeTrue();
 
-    $this->get('/system')->assertNotFound();
+    $this->get('/system')->assertForbidden();
 });
 
 it('allows system panel access for platform users with the required capability', function () {
diff --git a/tests/Feature/System/Spec113/AllowedTenantUniverseTest.php b/tests/Feature/System/Spec113/AllowedTenantUniverseTest.php
new file mode 100644
index 0000000..95be7cb
--- /dev/null
+++ b/tests/Feature/System/Spec113/AllowedTenantUniverseTest.php
@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Models\OperationRun;
+use App\Models\Tenant;
+use App\Services\System\AllowedTenantUniverse;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Validation\ValidationException;
+
+uses(RefreshDatabase::class);
+
+it('excludes the platform tenant from the allowed universe query (picker)', function () {
+    $platformTenant = Tenant::factory()->create([
+        'tenant_id' => null,
+        'external_id' => 'platform',
+        'name' => 'Platform',
+    ]);
+
+    $customerTenant = Tenant::factory()->create([
+        'external_id' => 'tenant-1',
+        'name' => 'Tenant One',
+    ]);
+
+    $universe = app(AllowedTenantUniverse::class);
+
+    $ids = $universe->query()->orderBy('id')->pluck('id')->all();
+
+    expect($ids)->toContain((int) $customerTenant->getKey());
+    expect($ids)->not->toContain((int) $platformTenant->getKey());
+});
+
+it('rejects attempts to target the platform tenant', function () {
+    $platformTenant = Tenant::factory()->create([
+        'tenant_id' => null,
+        'external_id' => 'platform',
+        'name' => 'Platform',
+    ]);
+
+    $universe = app(AllowedTenantUniverse::class);
+
+    expect(fn () => $universe->ensureAllowed($platformTenant))
+        ->toThrow(ValidationException::class);
+
+    expect(OperationRun::query()->count())->toBe(0);
+});
+
diff --git a/tests/Feature/System/Spec113/AuthorizationSemanticsTest.php b/tests/Feature/System/Spec113/AuthorizationSemanticsTest.php
new file mode 100644
index 0000000..c8ee510
--- /dev/null
+++ b/tests/Feature/System/Spec113/AuthorizationSemanticsTest.php
@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Models\PlatformUser;
+use App\Models\User;
+use App\Support\Auth\PlatformCapabilities;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+
+uses(RefreshDatabase::class);
+
+it('returns 404 when a tenant session accesses the system panel', function () {
+    $user = User::factory()->create();
+
+    $this->actingAs($user)->get('/system/login')->assertNotFound();
+
+    // Filament may switch the active guard within the test process,
+    // so ensure the tenant session is set for each request we assert.
+    $this->actingAs($user)->get('/system')->assertNotFound();
+});
+
+it('returns 403 when a platform user lacks the required capability', function () {
+    $platformUser = PlatformUser::factory()->create([
+        'capabilities' => [],
+        'is_active' => true,
+    ]);
+
+    $this->actingAs($platformUser, 'platform')
+        ->get('/system')
+        ->assertForbidden();
+});
+
+it('returns 200 when a platform user has the required capability', function () {
+    $platformUser = PlatformUser::factory()->create([
+        'capabilities' => [PlatformCapabilities::ACCESS_SYSTEM_PANEL],
+        'is_active' => true,
+    ]);
+
+    $this->actingAs($platformUser, 'platform')
+        ->get('/system')
+        ->assertSuccessful();
+});
+
diff --git a/tests/Feature/System/Spec113/SystemLoginThrottleTest.php b/tests/Feature/System/Spec113/SystemLoginThrottleTest.php
new file mode 100644
index 0000000..e89680a
--- /dev/null
+++ b/tests/Feature/System/Spec113/SystemLoginThrottleTest.php
@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Filament\System\Pages\Auth\Login;
+use App\Models\AuditLog;
+use App\Models\PlatformUser;
+use App\Models\Tenant;
+use Filament\Facades\Filament;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Livewire\Livewire;
+
+uses(RefreshDatabase::class);
+
+beforeEach(function () {
+    Filament::setCurrentPanel('system');
+    Filament::bootCurrentPanel();
+});
+
+it('throttles system login after repeated failures and still audits attempts', function () {
+    $platformTenant = Tenant::factory()->create([
+        'tenant_id' => null,
+        'external_id' => 'platform',
+        'name' => 'Platform',
+    ]);
+
+    $user = PlatformUser::factory()->create([
+        'email' => 'operator@tenantpilot.io',
+        'is_active' => true,
+    ]);
+
+    for ($i = 0; $i < 10; $i++) {
+        Livewire::test(Login::class)
+            ->set('data.email', $user->email)
+            ->set('data.password', 'wrong-password')
+            ->call('authenticate')
+            ->assertHasErrors(['data.email']);
+    }
+
+    Livewire::test(Login::class)
+        ->set('data.email', $user->email)
+        ->set('data.password', 'wrong-password')
+        ->call('authenticate')
+        ->assertHasErrors(['data.email']);
+
+    $auditCount = AuditLog::query()
+        ->where('tenant_id', $platformTenant->getKey())
+        ->where('action', 'platform.auth.login')
+        ->count();
+
+    expect($auditCount)->toBe(11);
+
+    $latestAudit = AuditLog::query()
+        ->where('tenant_id', $platformTenant->getKey())
+        ->where('action', 'platform.auth.login')
+        ->latest('id')
+        ->first();
+
+    expect($latestAudit)->not->toBeNull();
+    expect($latestAudit->metadata['reason'] ?? null)->toBe('throttled');
+});
+
diff --git a/tests/Feature/System/Spec113/SystemSessionIsolationTest.php b/tests/Feature/System/Spec113/SystemSessionIsolationTest.php
new file mode 100644
index 0000000..d572f79
--- /dev/null
+++ b/tests/Feature/System/Spec113/SystemSessionIsolationTest.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Str;
+
+uses(RefreshDatabase::class);
+
+it('sets a dedicated session cookie name for /system', function () {
+    $expectedCookieName = Str::slug((string) config('app.name', 'laravel')).'-system-session';
+
+    $this->get('/system/login')
+        ->assertSuccessful()
+        ->assertCookie($expectedCookieName);
+});
+