fix: release runtime status probes after checks

Chat startup and Runtime switching previously cached status-only Runtime instances, leaving managed OpenCode servers running without active conversations. Status checks now resolve the selected or configured default Runtime through a disposable probe and release it immediately.

Project execution Runtimes remain cached by model selection and execution space, preserving parallel work across different projects.

Release note: 修复启动或切换 Runtime 后空闲 OpenCode 服务持续驻留的问题；状态检查完成后会立即回收，多个项目仍可并行执行。

src/main/agent/selected-runtime-manager.ts

@@ -154,7 +154,16 @@ export class SelectedRuntimeManager implements SelectedRuntimeResolver {
   async getStatus(
     selection: AgentRuntimeSelection
   ): Promise<AgentRuntimeStatus> {
-    return (await this.getRuntime(selection)).getStatus()
+    if (this.disposed) {
+      throw new Error('Agent Runtime 正在关闭')
+    }
+    const operation = this.runStatusProbe(selection)
+    this.tests.add(operation)
+    try {
+      return await operation
+    } finally {
+      this.tests.delete(operation)
+    }
   }
 
   async testStatus(
@@ -276,6 +285,20 @@ export class SelectedRuntimeManager implements SelectedRuntimeResolver {
     }
   }
 
+  private async runStatusProbe(
+    selection: AgentRuntimeSelection
+  ): Promise<AgentRuntimeStatus> {
+    const runtime = await this.createRuntime(selection)
+    try {
+      if (this.disposed) {
+        throw new Error('Agent Runtime 正在关闭')
+      }
+      return await runtime.getStatus()
+    } finally {
+      await runtime.dispose()
+    }
+  }
+
   private async runNativeSnapshot(
     selection: AgentRuntimeSelection,
     executionSpace?: ExecutionSpaceDescriptor