feat(settings): add user-settings seam (ctx.settings) + file provider

Two-package capability family mirroring session-persistence/:

- dsh-settings: abstract Settings service — namespace registry with
  caller-fiber effect registrations, layered resolution (schema defaults
  < composition base < user document), schemastery validation,
  per-namespace deep-equal commit detection, and the settings/updated
  event. Boot/registration validation fails loud; provider publishes
  keep last-good per namespace.
- dsh-settings-local: settings.yaml/.json provider — resolveSpec
  defaulting to $DSH_HOME/settings.yaml, chokidar hot reload,
  content-equality self-write suppression, atomic 0600 tmp+rename
  writes, comment-preserving YAML namespace patching.

Consumers register inside ctx.inject(['settings'], …), so every
composition works unchanged without a mounted provider. Real Loader +
Include composition test proves cordis.yml boot and external-edit hot
propagation; HMR disposal test proves registry cleanup. Both packages
hold per-file 100% coverage.

Doc budgets rise 1705→1710 (AGENTS.md) and 835→845 (packages/README.md):
one structural line per file for the new package group.

Agent Note: .agents/notes/implemented/architecture/2026-07-28-user-settings-seam.md

packages/cordis/tool-cordis/src/api-catalog.ts

@@ -666,6 +666,28 @@ export const SERVICE_API: readonly ServiceApiEntry[] = [
       },
     ],
   },
+  {
+    key: 'settings',
+    summary: 'Abstract settings service.',
+    methods: [
+      {
+        signature: 'register<T>(ns: SettingsNamespace, schema: z<T>, options?: SettingsRegisterOptions<T>): SettingsScope<T>',
+        jsDoc: '/**\n * Register a namespace schema and receive its owner scope. The registration\n * is an effect on the calling plugin\'s fiber: disposing that fiber removes\n * the namespace and its observers. An invalid stored section fails the\n * registration itself — the earliest point where the schema can judge it.\n * @param ns - unique namespace; duplicate registration fails loud.\n * @param schema - schemastery schema resolving this namespace\'s value.\n * @param options - composition `base` layer and effect timing.\n * @returns the owner scope for reads, observation, and updates.\n */',
+      },
+      {
+        signature: 'describe(): SettingsDescriptor[]',
+        jsDoc: '/**\n * Describe every registered namespace for configuration surfaces.\n * @returns one descriptor per registered namespace, in registration order.\n */',
+      },
+      {
+        signature: 'get(ns: SettingsNamespace): unknown',
+        jsDoc: '/**\n * Read one registered namespace\'s resolved value.\n * @param ns - the namespace to read.\n * @returns the resolved value, or `undefined` while unregistered.\n */',
+      },
+      {
+        signature: 'async update(ns: SettingsNamespace, patch: object): Promise<void>',
+        jsDoc: '/**\n * Merge a patch into one registered namespace\'s user layer, validate the\n * resolved candidate, persist through the provider, then commit and emit.\n * A validation failure rejects before anything is persisted.\n * @param ns - the registered namespace to update.\n * @param patch - plain-object patch over the user section.\n */',
+      },
+    ],
+  },
   {
     key: 'skills',
     summary: 'Registry of skill providers.',
@@ -1188,6 +1210,13 @@ export const EVENT_API: readonly EventApiEntry[] = [
     jsDoc: '/**\n * Awaited parallel durability checkpoint: every listener runs and the\n * caller awaits all of them, with no waterfall veto. Dispatch through\n * {@link SessionStore.flush}. Scope-filtered dispatch\n * (`@deepseek-ai/dsh-scope`) reuses the session\'s owner scope.\n * @param session - the session whose buffered events must reach durable storage.\n * @dshScopeScan unsupported\n * @mode parallel\n */',
     summary: 'Awaited parallel durability checkpoint: every listener runs and the caller awaits all of them, with no waterfall veto.',
   },
+  {
+    name: 'settings/updated',
+    mode: 'emit',
+    signature: '\'settings/updated\'(ns: SettingsNamespace, next: unknown, prev: unknown, source: SettingsUpdateSource): void',
+    jsDoc: '/**\n * Committed change to one registered namespace\'s resolved value. Emitted\n * after the provider persisted (for `update`) or published (`provider`)\n * the change; never emitted when the resolved value is deep-equal.\n * @param ns - the namespace whose resolved value changed.\n * @param next - the new resolved value.\n * @param prev - the previous resolved value.\n * @param source - whether the change entered through `update()` or the provider.\n * @mode emit\n */',
+    summary: 'Committed change to one registered namespace\'s resolved value.',
+  },
   {
     name: 'slash/input-begin-command',
     mode: 'bail',
@@ -2181,6 +2210,26 @@ export const TYPE_API: readonly TypeApiEntry[] = [
     name: 'SessionTitleUserMessage',
     declaration: 'export interface SessionTitleUserMessage {\n    readonly seq: number;\n    readonly text: string;\n}',
   },
+  {
+    name: 'SettingsApplies',
+    declaration: 'export type SettingsApplies = \'live\' | \'restart\';',
+  },
+  {
+    name: 'SettingsDescriptor',
+    declaration: 'export interface SettingsDescriptor {\n    ns: SettingsNamespace;\n    schema: unknown;\n    value: unknown;\n    applies: SettingsApplies;\n}',
+  },
+  {
+    name: 'SettingsNamespace',
+    declaration: 'export type SettingsNamespace = Branded<\'SettingsNamespace\'>;',
+  },
+  {
+    name: 'SettingsRegisterOptions',
+    declaration: 'export interface SettingsRegisterOptions<T> {\n    base?: Partial<T>;\n    applies?: SettingsApplies;\n}',
+  },
+  {
+    name: 'SettingsScope',
+    declaration: 'export interface SettingsScope<T> {\n    get(): T;\n    watch(callback: (next: T, prev: T) => void): () => void;\n    update(patch: object): Promise<void>;\n}',
+  },
   {
     name: 'SkillCandidate',
     declaration: 'export interface SkillCandidate extends SkillSummary {\n    readonly rank: number;\n    readonly locator: unknown;\n    readonly path?: string;\n    readonly metadata?: Readonly<Record<string, unknown>>;\n}',