fix(settings): harden seam and provider per review findings

Confirmed and fixed, each with a regression test that failed first:

- Concurrent update() lost patches (merge over one stale snapshot):
  per-namespace serialized write queues; a failed write cannot poison
  the queue for later writers.
- Fixed-name .tmp write followed planted symlinks and kept stale modes:
  random-suffix sibling, exclusive-create (wx), 0600, cleanup on
  failure, then rename.
- A throwing settings/updated listener escaped commit and permanently
  wedged the provider reload chain (rejected refreshTask): commit now
  contains listener failures (INVARIANT-coded errors still propagate),
  async watcher rejections are adopted and contained
  (watch callbacks are officially void | Promise<void>), and the
  provider chains refreshes on a settled tail with an error log.
- No way to remove a user override: scope/service replace(section)
  sets the user section wholesale; replace({}) re-inherits base and
  schema defaults.
- The three-primitive provider contract did not hold (base never
  called load()): the base Service.init loads and publishes once;
  settings-local delegates via yield* super[Service.init]().
- Dispose did not quiesce: teardown flags closed, closes the watcher,
  then awaits queued/in-flight reloads; closed is re-checked across
  await points.
- Invariant now checks the authoritative relation with the seam's own
  deepEqualJson: emitted next must equal settings.get(ns), and
  next/prev must differ structurally (cosmokit dependency dropped).
- New docs/core-data-structures/settings.{md,zh.md} with type-equiv
  blocks + manifest entries; catalog types moved from exemptions to
  LINK_MAP; website page registered.

Both packages stay at per-file 100% coverage.

docs/core-data-structures/settings.zh.md

@@ -0,0 +1,94 @@
+# 用户设置
+
+[English](settings.md) | 中文
+
+[dsh-settings](../../packages/settings/settings) 的用户设置 seam 持有一份按 namespace 分节的用户文档，并把每个已注册 namespace 解析为：schema 默认值，然后注册方的组合 `base`，最后用户分节。[dsh-settings-local](../../packages/settings/settings-local) 这类 provider 存储原始文档并推送外部编辑；消费插件注册 schema 后读取或观察解析值。组合配置仍留在 `cordis.yml`——namespace 只承载用户可编辑子集。
+
+Source: [`packages/settings/settings/src/index.ts`](../../packages/settings/settings/src/index.ts)
+
+## 标识
+
+namespace 命名用户文档中一个插件所有的分节。brand 使其不与其他跨边界 id 混用；构造时校验小写 kebab-case 形态。
+
+```ts type-equiv
+/** Nominal id of one registered settings namespace. */
+type SettingsNamespace = Branded<'SettingsNamespace'>
+```
+
+## 注册
+
+注册把 schemastery schema 绑定到调用方插件 fiber 上的 namespace——dispose 该 fiber 即移除 namespace 及其观察者。options 携带组合层与 owner 的生效时机。
+
+```ts type-equiv
+/** Registration options beyond the namespace schema. */
+interface SettingsRegisterOptions<T> {
+  /** Composition-layer values resolved below the user layer (entry-config subset). */
+  base?: Partial<T>
+  /** Owner's effect timing, surfaced to configuration UIs; defaults to `live`. */
+  applies?: SettingsApplies
+}
+```
+
+`applies` 是 UI 提示而非机制：`restart` 的 owner 只是从不 watch，其值在构造期读取一次，配置界面可为待生效变更加标。
+
+```ts type-equiv
+/** When a namespace's changes take effect for its owner. */
+type SettingsApplies = 'live' | 'restart'
+```
+
+## Owner scope
+
+scope 是面向 owner 的句柄。`update` 把稀疏 patch 只合并进用户分节（绝不进 `base`）；`replace` 整体替换分节，是删除/重置路径——替换中缺席的键重新继承 `base` 与 schema 默认值。同一 namespace 的写入按调用顺序串行，解析值是深冻结快照。
+
+```ts type-equiv
+/** Owner-facing handle for one registered namespace. */
+interface SettingsScope<T> {
+  /** Current resolved value: schema defaults, then `base`, then the user layer. */
+  get(): T
+  /**
+   * Observe committed changes to this namespace's resolved value. A callback
+   * may be async; a rejection is contained and logged like a sync throw.
+   * @param callback - invoked after each commit with the next and previous values.
+   * @returns the disposer removing this observer.
+   */
+  watch(callback: (next: T, prev: T) => void | Promise<void>): () => void
+  /**
+   * Merge a partial patch into this namespace's user layer and persist it.
+   * @param patch - plain-object patch over the user section.
+   */
+  update(patch: object): Promise<void>
+  /**
+   * Replace this namespace's user section wholesale; absent keys re-inherit
+   * the composition `base` and schema defaults (`replace({})` resets all).
+   * @param section - the complete next user section.
+   */
+  replace(section: object): Promise<void>
+}
+```
+
+## 描述符
+
+`describe()` 为配置界面序列化每个已注册 namespace：schemastery 的 `toJSON()` 信封驱动 schema 渲染的表单，解析值填充表单。
+
+```ts type-equiv
+/** One registered namespace as surfaced to configuration UIs. */
+interface SettingsDescriptor {
+  /** The registered namespace. */
+  ns: SettingsNamespace
+  /** Serialized schemastery schema (`schema.toJSON()`). */
+  schema: unknown
+  /** Current resolved value. */
+  value: unknown
+  /** Owner's declared effect timing. */
+  applies: SettingsApplies
+}
+```
+
+## 变更提交
+
+每次提交的变更——进程内写入或 provider 观察到的外部编辑——在新值成为权威值之后发出 `settings/updated (ns, next, prev, source)`，解析值深相等时绝不发出。source 标记区分两条入口路径。
+
+```ts type-equiv
+/** Origin of one committed settings change. */
+type SettingsUpdateSource = 'update' | 'provider'
+```