fix(plugins): draft metadata survives a remount, plugin commands follow the composer lock

Draft metadata was component state while the prompt lived in the draft store, so a composer that
remounted across the compact breakpoint kept its text and lost the plugin's choices. It now lives
in the draft store beside the prompt, is cleared when the draft is sent, and is not cleared when
the prompt is emptied. It is not persisted across app restarts.

While the New workspace composer is creating the agent, the built-in controls are disabled but
plugin controls and commands were not. They read the composer's own lock: Paseo controls render
disabled, and setPrompt, insertText and the agent commands refuse.

The options and metadata a plugin reads are frozen copies, through the same helper the timeline
projection uses. The composer control test mounted components in JSDOM, which the testing rules
ban; it now runs in the browser project.

public-docs/plugins/reference.md

@@ -1972,6 +1972,11 @@ callback, so `await composer.setProvider("codex")` followed by `await composer.s
 changes both. A command's promise resolves once the change has taken effect, and `composer.agent`
 shows it on the next render.
 
+While the New workspace screen creates the workspace and its agent, the composer is locked. Your
+controls render disabled, `setPrompt` and `insertText` throw, and the agent commands reject with
+"The composer is locked while the agent is being created." `composer.agent.options` and
+`composer.agent.metadata` are frozen copies; change them through `setOptions` and `setMetadata`.
+
 A composer item counts toward how much fits before Paseo knows what it renders. An item that
 renders nothing can still leave an empty overflow sheet on a narrow composer, so always render a
 control.

public-docs/plugins/reference.zh-CN.md

@@ -1659,6 +1659,8 @@ export default function contribute(client: PluginClientContext) {
 
 每个命令都按运行时 composer 的当前状态执行，而不是按创建回调的那次渲染，所以 `await composer.setProvider("codex")` 之后再 `await composer.setModel("gpt")` 会同时生效。命令的 Promise 在更改生效后完成，`composer.agent` 在下一次渲染时反映它。
 
+新建工作区界面在创建工作区及其 Agent 期间会锁定 composer。你的控件显示为禁用，`setPrompt` 和 `insertText` 会抛出错误，Agent 命令会以 "The composer is locked while the agent is being created." 拒绝。`composer.agent.options` 和 `composer.agent.metadata` 是冻结的副本；请通过 `setOptions` 和 `setMetadata` 修改它们。
+
 在 Paseo 知道渲染结果之前，composer 项就已计入可容纳的数量。不渲染任何内容的项仍可能在窄 composer 上留下空的溢出面板，所以请始终渲染一个控件。
 
 [Composer 控件示例](https://github.com/getpaseo/paseo/tree/main/plugin-examples/composer-controls)注册了一个 `Select`、两个 `Toggle`（其中一个写入 Provider 选项）和一个 `Action`。