Host Directory Picker

The web GUI host's workspace-directory picker is a capability seam. The abstract `DirectoryPicker` service (`ctx.directoryPicker`) is its Service Definition. Its only method, `capability()`, returns a discriminated union describing how an operator selects a directory. Backends differ in user interaction, not just implementation: `{ kind: 'native', pick(signal) }` opens one native OS chooser on the host display ([`-native`](../directory-picker-native/README.md)); `{ kind: 'browse', list(path?), createDirectory(path, name) }` provides listing and creation operations for an in-app browser, which works for remote clients that cannot reach an OS chooser ([`-browse`](../directory-picker-browse/README.md)). Consumers switch on `capability().kind`; the union derives from the merge-extensible `DirectoryPickerCapabilities` map, and a new backend adds its variant there through declaration merging. For an unknown kind, consumers hide directory picking rather than fail. The capability object must be stable for the service lifetime. Each backend package also has a browser entrypoint that registers the matching interaction in ui-workspace's directory-flow slots, so one composition row selects both the host capability and the client flow. A composition that should choose at runtime mounts [`-auto`](../directory-picker-auto/README.md), which inspects the host once at boot and mounts the matching backend row.

• 适用 Agent：DeepSeek Harness
• 适配模型：DeepSeek

@deepseek-ai/dsh-host-directory-picker

暂无通过审核、可复现的同任务 A/B 运行证据；本档案仅证明来源可信，不代表实测有效。