Enable runtime YAML export for copy workflows

Add a read-only runtime export command that emits apply-compatible YAML for existing container runtimes and endpoints, plus docs and integration coverage. Keep the implementation bounded to fields already accepted by the runtime YAML parser.

Constraint: Export output must round-trip through ar runtime apply without carrying server-owned IDs or status fields.

Rejected: Reconstructing cloudBuild from remote runtime state | cloudBuild depends on local source and build settings that are not recoverable from the service.

Confidence: high

Scope-risk: narrow

Directive: Treat exported registry auth as sensitive if returned by the service; review YAML before sharing.

Tested: ruff check src/ tests/; ruff format --check src/ tests/; mypy src/agentrun_cli; pytest tests/integration/test_runtime_cmd.py -v; pytest tests/unit tests/integration --cov=agentrun_cli --cov-fail-under=95; live cn-hangzhou export/apply/status smoke for cli-export-verify-20260609213323.

Change-Id: Ib7d4b629bbb2e377213b3aa302d7d78d13c7f066
Co-developed-by: Codex <noreply@openai.com>
Not-tested: cleanup/delete of live verification runtime was intentionally not performed without explicit deletion confirmation.
Signed-off-by: congxiao.wxx <congxiao.wxx@alibaba-inc.com>

Author: congxiao-wxx

docs/en/runtime.md

@@ -19,6 +19,7 @@ Also available as the alias `ar rt`.
 - [apply](#apply) — cloud-build when configured, then create-or-update from YAML.
 - [cloud-build](#cloud-build) — build images from YAML without deploying.
 - [render](#render) — dry-run validate + render to SDK input.
+- [export](#export) — export one existing runtime as apply-ready YAML.
 - [get](#get) — fetch one runtime by name.
 - [list](#list) — list runtimes; filter by `--created-by-cli` or `--workspace`.
 - [delete](#delete) — delete a runtime (waits by default).
@@ -157,6 +158,41 @@ before `apply`.
 
 ---
 
+## export
+
+```
+ar runtime export NAME [-f FILE]
+```
+
+Export an existing Agent Runtime and its endpoints as `ar runtime apply` YAML.
+The command writes YAML to stdout by default, or to `--file` when provided. It
+exports only fields supported by the CLI YAML schema and intentionally omits
+server-owned state such as IDs, ARNs, versions, status, and timestamps.
+`cloudBuild` cannot be reconstructed from a remote runtime because it depends on
+local source/build settings.
+If the service returns registry authentication details, the exported YAML may
+contain sensitive values; review it before committing or sharing.
+
+### Options
+
+| Flag | Type | Required | Default | Description |
+|------|------|----------|---------|-------------|
+| `-f`, `--file` | path | no |  | Write YAML to a file instead of stdout. |
+
+### Examples
+
+```bash
+# Export to stdout.
+ar runtime export my-agent
+
+# Export, edit metadata.name, then create a copy.
+ar runtime export my-agent -f copied-runtime.yaml
+# edit copied-runtime.yaml: metadata.name: my-agent-copy
+ar runtime apply -f copied-runtime.yaml
+```
+
+---
+
 ## get
 
 ```

docs/zh/runtime.md

@@ -16,6 +16,7 @@ YAML；用户不写时 CLI 会自动注入一个名为 `default` 的 endpoint（
 - [apply](#apply) — 配置后先云上构建，再从 YAML create-or-update。
 - [cloud-build](#cloud-build) — 只按 YAML 构建镜像，不部署 runtime。
 - [render](#render) — 校验 + 渲染为 SDK 输入（不调用服务端）。
+- [export](#export) — 将存量 runtime 导出为可 apply 的 YAML。
 - [get](#get) — 按名字获取单个 runtime。
 - [list](#list) — 列出 runtime；可用 `--created-by-cli` 或 `--workspace` 过滤。
 - [delete](#delete) — 删除 runtime（默认等待）。
@@ -148,6 +149,38 @@ ar runtime render -f FILE
 
 ---
 
+## export
+
+```
+ar runtime export NAME [-f FILE]
+```
+
+读取一个存量 Agent Runtime 及其 endpoints，并导出为 `ar runtime apply` 可消费的
+YAML。默认输出到 stdout；传入 `--file` 时写入文件。命令只导出当前 CLI YAML
+schema 支持的字段，会刻意省略 ID、ARN、version、status、时间戳等服务端状态字段。
+`cloudBuild` 依赖本地源码目录和构建参数，无法从远端 runtime 反推，因此不会导出。
+如果服务端返回镜像仓库认证信息，导出的 YAML 可能包含敏感值；提交或共享前请先检查。
+
+### Options
+
+| Flag | Type | Required | Default | Description |
+|------|------|----------|---------|-------------|
+| `-f`, `--file` | path | no |  | 将 YAML 写入文件，而不是 stdout。 |
+
+### Examples
+
+```bash
+# 导出到 stdout
+ar runtime export my-agent
+
+# 导出后修改 metadata.name，再创建一份副本
+ar runtime export my-agent -f copied-runtime.yaml
+# 编辑 copied-runtime.yaml：metadata.name: my-agent-copy
+ar runtime apply -f copied-runtime.yaml
+```
+
+---
+
 ## get
 
 ```

src/agentrun_cli/_utils/cloud_build.py

@@ -323,13 +323,14 @@ def _artifact_name() -> str:
 
 def _go_platform() -> str:
     """Convert a Python platform name to a Go release platform name."""
-    if sys.platform == "win32":
+    platform_name = str(sys.platform)
+    if platform_name == "win32":
         return "windows"
-    if sys.platform == "darwin":
+    if platform_name == "darwin":
         return "darwin"
-    if sys.platform.startswith("linux"):
+    if platform_name.startswith("linux"):
         return "linux"
-    raise CloudBuildError(f"unsupported platform: {sys.platform}")
+    raise CloudBuildError(f"unsupported platform: {platform_name}")
 
 
 def _go_arch() -> str:

src/agentrun_cli/commands/runtime/__init__.py

@@ -20,6 +20,7 @@
 )
 from agentrun_cli.commands.runtime import crud_cmd as _crud_mod  # noqa: E402
 from agentrun_cli.commands.runtime import delete_cmd as _delete_mod  # noqa: E402
+from agentrun_cli.commands.runtime import export_cmd as _export_mod  # noqa: E402
 from agentrun_cli.commands.runtime import render_cmd as _render_mod  # noqa: E402
 from agentrun_cli.commands.runtime import status_cmd as _status_mod  # noqa: E402
 
@@ -35,6 +36,7 @@ def runtime_group():
 runtime_group.add_command(_apply_mod.apply_cmd)
 runtime_group.add_command(_cloud_build_mod.cloud_build_cmd)
 runtime_group.add_command(_render_mod.render_cmd)
+runtime_group.add_command(_export_mod.export_cmd)
 runtime_group.add_command(_crud_mod.get_cmd)
 runtime_group.add_command(_crud_mod.list_cmd)
 runtime_group.add_command(_delete_mod.delete_cmd)