refactor(gui): slot system standard — single register, four props shares, framework store seat

The definitive slot model for the web client, replacing the first-generation
define/register two-step, ScopedSlots whitelist faces, and binding handles:

- 'root' is the only a-priori slot (SlotsService built-in); the shell renders
  exactly ctx.slots.renderSlot('root', {}).
- register is the single API: children = slot declaration + render
  authorization + runtime spec in one options object; misconfiguration fails
  loud at load (duplicate declaration, undeclared contribution, one store
  handle under two scopes).
- Component props arrive in four auto-derived shares: PropsRuntime<K>
  (owner params + session/global standard kits via declare-merge),
  PropsRenderSlots<S>, PropsStore<H>, and the inject business face.
  sessionId is framework-supplied; hooks are framework-made only.
- Framework store seat: defineStore factories declare schema/actions/persist;
  read = useStore, write = baked actions only; store scope derives from the
  mounting entry; per-session persist keys and clearPersisted lifecycle.
- inject factories read the apply closure's own ctx (binding handles retired;
  root-ctx back door closed); SessionProvider is self-wired render-prop.
- Rendering sits behind the SlotRenderer install seam; runtime stays
  React-free; ownership ledger keyed to the single entry axis closes the
  stale-authority window (StaleAuthorizationError probes).

Docs: the slot type-chain note is refreshed in place as the slot system
standard RFC (bilingual pair re-recorded); the web client architecture RFC
defers its slot sections there; packages/client/AGENTS.md gains the slot and
props discipline; gui-testing/web-styling notes drop missions/ references.

Tests: suites rewritten to the standard (props fed directly, real store
engines via createXXXStore().create(), no render machinery); load-time
negative samples for declaration/authorization/store conflicts; verified by
real-host playwright run (three columns, empty state, collapse, keyed session
remount, cross-slot selection sharing).

docs(ui-sidebar): point contract reference at the committed slot standard RFC

missions/ is workspace-local and never committed; the README must not cite it.

packages/client/ui-layout/tests/layout-store.spec.ts

@@ -0,0 +1,73 @@
+// @vitest-environment jsdom
+/**
+ * createLayoutStore unit account: init shape, the action write set (clamp
+ * inside actions), and the persist key round-trip over jsdom localStorage.
+ * Uses the test-sanctioned path: factory self-call + .create() gives the
+ * real engine instance (same create path as production).
+ */
+import { beforeEach, describe, expect, it } from 'vitest'
+import { createLayoutStore } from '@deepseek-ai/dsh-client-ui-layout/src/client/stores.ts'
+import {
+  DETAILS_DEFAULT, DETAILS_MAX, DETAILS_MIN,
+  SIDEBAR_DEFAULT, SIDEBAR_MAX, SIDEBAR_MIN,
+} from '@deepseek-ai/dsh-client-ui-layout/src/client/columns.ts'
+
+const PERSIST_KEY = 'dsh.layout.panels'
+
+beforeEach(() => { localStorage.clear() })
+
+describe('createLayoutStore', () => {
+  it('initializes with sidebar open at default and details closed', () => {
+    const { store } = createLayoutStore().create()
+    expect(store.getSnapshot()).toEqual({ sidebar: SIDEBAR_DEFAULT, details: 0 })
+  })
+
+  it('each create() is an independent instance (factory is not a singleton)', () => {
+    const a = createLayoutStore().create()
+    const b = createLayoutStore().create()
+    a.actions.setSidebar(400)
+    expect(b.store.getSnapshot().sidebar).toBe(SIDEBAR_DEFAULT)
+  })
+
+  it('setSidebar/setDetails clamp into the contract ranges', () => {
+    const { store, actions } = createLayoutStore().create()
+    actions.setSidebar(1)
+    expect(store.getSnapshot().sidebar).toBe(SIDEBAR_MIN)
+    actions.setSidebar(9999)
+    expect(store.getSnapshot().sidebar).toBe(SIDEBAR_MAX)
+    actions.setDetails(1)
+    expect(store.getSnapshot().details).toBe(DETAILS_MIN)
+    actions.setDetails(9999)
+    expect(store.getSnapshot().details).toBe(DETAILS_MAX)
+  })
+
+  it('toggleSidebar flips closed <-> contract default (drag width forgotten)', () => {
+    const { store, actions } = createLayoutStore().create()
+    actions.setSidebar(400)
+    actions.toggleSidebar()
+    expect(store.getSnapshot().sidebar).toBe(0)
+    actions.toggleSidebar()
+    expect(store.getSnapshot().sidebar).toBe(SIDEBAR_DEFAULT)
+  })
+
+  it('openDetails is a no-op when already open; closeDetails zeroes', () => {
+    const { store, actions } = createLayoutStore().create()
+    actions.openDetails()
+    expect(store.getSnapshot().details).toBe(DETAILS_DEFAULT)
+    actions.setDetails(500)
+    actions.openDetails()
+    expect(store.getSnapshot().details).toBe(500)
+    actions.closeDetails()
+    expect(store.getSnapshot().details).toBe(0)
+  })
+
+  it('persists under dsh.layout.panels and rehydrates on the next create', () => {
+    const first = createLayoutStore().create()
+    first.actions.setSidebar(320)
+    first.actions.openDetails()
+    expect(JSON.parse(localStorage.getItem(PERSIST_KEY) ?? '{}')).toEqual({ sidebar: 320, details: DETAILS_DEFAULT })
+
+    const second = createLayoutStore().create()
+    expect(second.store.getSnapshot()).toEqual({ sidebar: 320, details: DETAILS_DEFAULT })
+  })
+})