Accept POST on system metrics for compatibility

Allow both GET and POST requests on /api/system/metrics and cover the compatibility path in feature and control-plane contract tests.

Author: durable-workflow-ops

routes/api.php

@@ -174,7 +174,7 @@
     // ── System / Operations ─────────────────────────────────────────
     Route::prefix('system')->middleware([$admin, $cpv, $ns])->group(function () {
         Route::get('/health', [SystemController::class, 'health']);
-        Route::get('/metrics', [SystemController::class, 'metrics']);
+        Route::match(['get', 'post'], '/metrics', [SystemController::class, 'metrics']);
         Route::get('/operator-metrics', [SystemController::class, 'operatorMetrics']);
         Route::get('/repair', [SystemController::class, 'repairStatus']);
         Route::post('/repair/pass', [SystemController::class, 'repairPass']);

tests/Feature/ControlPlaneOperationalSuccessContractTest.php

@@ -147,6 +147,39 @@ public static function operationalSuccessProvider(): array
                     ],
                 ],
             ],
+            'system.metrics_empty_post' => [
+                'method' => 'post',
+                'path' => '/api/system/metrics',
+                'body' => [],
+                'structure' => [
+                    'generated_at',
+                    'namespace',
+                    'metrics' => [
+                        'dw_workflow_task_consecutive_failures' => [
+                            'max_consecutive_failures',
+                            'failed_task_count',
+                            'workflow_type_count',
+                            'workflow_type_limit',
+                            'workflow_types_truncated',
+                            'suppressed_workflow_type_count',
+                            'suppressed_failed_task_count',
+                            'label_cardinality_policy',
+                            'by_workflow_type',
+                        ],
+                        'dw_projection_drift_total' => [
+                            'total',
+                            'table_count',
+                            'tables_with_drift',
+                            'scope',
+                            'label_cardinality_policy',
+                            'by_table',
+                        ],
+                    ],
+                    'cardinality' => [
+                        'metric_label_sets',
+                    ],
+                ],
+            ],
             'system.health_empty' => [
                 'method' => 'get',
                 'path' => '/api/system/health',

tests/Feature/ControlPlaneVersionCoverageTest.php

@@ -125,6 +125,7 @@ public static function controlPlaneEndpointProvider(): array
             // SystemController
             'system.health' => ['method' => 'get', 'path' => '/api/system/health'],
             'system.metrics' => ['method' => 'get', 'path' => '/api/system/metrics'],
+            'system.metrics_post' => ['method' => 'post', 'path' => '/api/system/metrics'],
             'system.operator_metrics' => ['method' => 'get', 'path' => '/api/system/operator-metrics'],
             'system.repair_status' => ['method' => 'get', 'path' => '/api/system/repair'],
             'system.repair_pass' => ['method' => 'post', 'path' => '/api/system/repair/pass'],

tests/Feature/SystemMetricsTest.php

@@ -73,6 +73,26 @@ public function test_system_metrics_reports_bounded_workflow_task_failure_series
         ], $response->json('metrics.dw_workflow_task_consecutive_failures.by_workflow_type'));
     }
 
+    public function test_system_metrics_accepts_post_requests_for_compatibility(): void
+    {
+        config(['server.metrics.workflow_task_failure_type_limit' => 2]);
+
+        $this->createWorkflowTaskMetricRow('tests.metric-high', 7);
+        $this->createWorkflowTaskMetricRow('tests.metric-middle', 3);
+
+        $getResponse = $this->getJson('/api/system/metrics', $this->controlPlaneHeadersWithWorkerProtocol());
+        $postResponse = $this->postJson('/api/system/metrics', [], $this->controlPlaneHeadersWithWorkerProtocol());
+
+        $getResponse->assertOk()
+            ->assertHeader(ControlPlaneProtocol::HEADER, ControlPlaneProtocol::VERSION);
+        $postResponse->assertOk()
+            ->assertHeader(ControlPlaneProtocol::HEADER, ControlPlaneProtocol::VERSION)
+            ->assertJsonPath('namespace', 'default');
+
+        $this->assertSame($getResponse->json('metrics'), $postResponse->json('metrics'));
+        $this->assertSame($getResponse->json('cardinality'), $postResponse->json('cardinality'));
+    }
+
     public function test_system_metrics_reports_projection_drift_by_fixed_table_inventory(): void
     {
         $this->createWorkflowTaskMetricRow('tests.projection-drift', 1);