### Build and call a HarnessAgent with DockerFilesystemSpec

Source: https://java.agentscope.io

Builds a HarnessAgent with a model resolved via ModelRegistry (reads DASHSCOPE_API_KEY), a workspace directory, and a DockerFilesystemSpec sandboxed to the current user. The agent is then called with a RuntimeContext specifying session and user IDs, blocking until the response completes.

```java
var agent = HarnessAgent.builder()
    .name("coder")
    .model("dashscope:qwen-max")                                // resolved via ModelRegistry; reads DASHSCOPE_API_KEY
    .workspace(Paths.get(".agentscope/workspace"))   // AGENTS.md · MEMORY.md · skills · subagents
    .filesystem(new DockerFilesystemSpec()           // sandboxed exec: local · Docker · remote KV swap in one line
        .isolationScope(IsolationScope.USER))           // shared across sessions of the same user
    .build();
agent.call(msg, RuntimeContext.builder()
    .sessionId("demo").userId("alice").build()).block();
```

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