Surface backend admission severity rollup on dw system:operator-metrics

Renders the workflow-v2 admission-roll-up severity rollup that the
Phase 6 rollout-safety contract pins on `operator_metrics.backend.severity`
on the operator-metrics CLI surface so HTTP-only operators can read the
worst-case admission severity (`error` > `warning` > `info` > `ok`)
directly from `dw system:operator-metrics` without walking the
`backend.issues` array themselves.

`OperatorMetricsCommand::renderBackend()` now emits one new row right
after the existing `Supported:` row:

  Severity:             <error|warning|info|ok>

The row degrades gracefully when the snapshot predates the contract
(workflow alpha < 2.0.0-alpha.13, where a0badea "Surface backend
admission severity rollup on operator metrics" is not yet on a
published tag): the renderer omits the row and the existing per-issue
severity rendering still surfaces individual issue severities.

Pins `backend.severity` on `schemas/output/operator-metrics.schema.json`
next to the existing `backend.supported` key, and adds
`test_operator_metrics_schema_pins_backend_severity_key`,
`test_operator_metrics_command_renders_backend_severity_rollup`, and
`test_operator_metrics_command_omits_backend_severity_when_snapshot_predates_contract`
to guard the schema declaration, the renderer, and the renderer fallback.

Author: durable-workflow-ops

schemas/output/operator-metrics.schema.json

@@ -90,6 +90,7 @@
           "type": "object",
           "properties": {
             "supported": { "type": ["boolean", "null"] },
+            "severity": { "type": ["string", "null"] },
             "database": { "type": ["object", "null"], "additionalProperties": true },
             "queue": { "type": ["object", "null"], "additionalProperties": true },
             "cache": { "type": ["object", "null"], "additionalProperties": true },

src/Commands/SystemCommand/OperatorMetricsCommand.php

@@ -315,6 +315,10 @@ private function renderBackend(OutputInterface $output, array $backend): void
         $output->writeln('<info>Backend capabilities (admission roll-up)</info>');
         $output->writeln(sprintf('  Supported:            %s', $supported ? 'yes' : 'no'));
 
+        if (is_string($backend['severity'] ?? null) && $backend['severity'] !== '') {
+            $output->writeln(sprintf('  Severity:             %s', $backend['severity']));
+        }
+
         foreach (['database', 'queue', 'cache'] as $component) {
             $detail = is_array($backend[$component] ?? null) ? $backend[$component] : [];
             $label = match ($component) {

tests/Commands/SystemCommandTest.php

@@ -554,6 +554,7 @@ public function test_operator_metrics_command_renders_rollout_safety_signals():
         self::assertStringContainsString('build-2026.04.24', $display);
 
         self::assertStringContainsString('Supported:            yes', $display);
+        self::assertStringContainsString('Severity:             ok', $display);
         self::assertStringContainsString('Database:              mysql/mysql', $display);
         self::assertStringContainsString('Cache:                 redis/redis', $display);
 
@@ -792,6 +793,69 @@ public function test_operator_metrics_command_omits_dispatch_failed_age_when_sna
         self::assertStringContainsString('dispatch failed 2', $display);
     }
 
+    public function test_operator_metrics_schema_pins_backend_severity_key(): void
+    {
+        $schema = json_decode(
+            (string) file_get_contents(__DIR__.'/../../schemas/output/operator-metrics.schema.json'),
+            true,
+            flags: JSON_THROW_ON_ERROR,
+        );
+
+        $backend = $schema['properties']['operator_metrics']['properties']['backend']['properties'];
+
+        self::assertSame(['boolean', 'null'], $backend['supported']['type']);
+        self::assertSame(['string', 'null'], $backend['severity']['type']);
+    }
+
+    public function test_operator_metrics_command_renders_backend_severity_rollup(): void
+    {
+        $payload = self::operatorMetricsPayload();
+        $payload['operator_metrics']['backend'] = [
+            'supported' => false,
+            'severity' => 'error',
+            'database' => ['connection' => 'mysql', 'driver' => 'mysql'],
+            'queue' => ['connection' => 'sync', 'driver' => 'sync'],
+            'cache' => ['store' => 'array', 'driver' => 'array'],
+            'issues' => [
+                [
+                    'component' => 'queue',
+                    'code' => 'queue_sync_unsupported',
+                    'severity' => 'error',
+                    'summary' => 'Workflow v2 cannot run on the sync queue connection.',
+                ],
+            ],
+        ];
+
+        $command = new OperatorMetricsCommand();
+        $command->setServerClient(new SystemFakeClient($payload));
+
+        $tester = new CommandTester($command);
+        self::assertSame(Command::SUCCESS, $tester->execute([]));
+
+        $display = $tester->getDisplay();
+
+        self::assertStringContainsString('Supported:            no', $display);
+        self::assertStringContainsString('Severity:             error', $display);
+        self::assertStringContainsString('[error] Workflow v2 cannot run on the sync queue connection.', $display);
+    }
+
+    public function test_operator_metrics_command_omits_backend_severity_when_snapshot_predates_contract(): void
+    {
+        $payload = self::operatorMetricsPayload();
+        unset($payload['operator_metrics']['backend']['severity']);
+
+        $command = new OperatorMetricsCommand();
+        $command->setServerClient(new SystemFakeClient($payload));
+
+        $tester = new CommandTester($command);
+        self::assertSame(Command::SUCCESS, $tester->execute([]));
+
+        $display = $tester->getDisplay();
+
+        self::assertStringNotContainsString('Severity:', $display);
+        self::assertStringContainsString('Supported:            yes', $display);
+    }
+
     public function test_operator_metrics_schema_pins_run_summary_missing_age_keys(): void
     {
         $schema = json_decode(
@@ -962,6 +1026,7 @@ private static function operatorMetricsPayload(): array
                 ],
                 'backend' => [
                     'supported' => true,
+                    'severity' => 'ok',
                     'database' => ['connection' => 'mysql', 'driver' => 'mysql'],
                     'queue' => ['connection' => 'redis', 'driver' => 'redis'],
                     'cache' => ['store' => 'redis', 'driver' => 'redis'],