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/runtime/src/client/index.ts

@@ -1,21 +1,27 @@
 /**
  * Browser half: the whole runtime contract surface (api-contracts v3 §4) —
- * SlotsService, SessionsService (list store + scope tree + object layer),
- * the ClientLoader interface, and the cordis Context/Events merges. apply
+ * SlotsService (declaration ledger + renderer seam + store axis, built-in
+ * 'root'), SessionsService (list store + current selection + scope tree +
+ * object layer), the ClientLoader interface, and the cordis Context/Events
+ * merges. apply
  * mounts ctx.slots + ctx.sessions and wires the connection stream loop into
  * the object layer. The loader machinery implementation is NOT in the plugin
  * bundle — it ships via the package's `./loader` subpath, statically held by
  * the web shell (a loader cannot load itself).
  */
 import type { Context } from 'cordis'
-import type { ConnectionHandle } from '@deepseek-ai/dsh-client-connection/client'
-import type { SessionBinding as GenericSessionBinding } from '@deepseek-ai/dsh-client-ui-slots'
+import type { ConnectionHandle, SessionId } from '@deepseek-ai/dsh-client-connection/client'
+import type { SnapshotSelectorHook } from '@deepseek-ai/dsh-client-ui-slots'
 import type { SnapshotStore, UseSession } from '@deepseek-ai/dsh-client-web-react'
 import { SlotsService } from './slots.ts'
 import { SessionsService } from './sessions/service.ts'
+import type { SessionListState } from './sessions/service.ts'
 import type { ConversationSnapshot, RunningToolCall, ToolResultNode } from './sessions/conversation.ts'
 
 export { SlotsService } from './slots.ts'
+// RootOwnerProps rides the 'root' SlotMap row (both migrated here from
+// ui-layout: the framework slot is declared by the framework package).
+export type { RootOwnerProps } from './slots.ts'
 export { SessionsService, scopeOf } from './sessions/service.ts'
 export type { Session } from './sessions/session.ts'
 export type { SessionBinding, SessionListState, SessionSummary } from './sessions/service.ts'
@@ -38,9 +44,6 @@ export type { SessionId } from '@deepseek-ai/dsh-client-connection/client'
  */
 export type ClientContext = Context
 
-/** SessionBinding narrowed to the client context (inject factories dot services directly). */
-export type ClientSessionBinding = GenericSessionBinding<ClientContext>
-
 /** The conversation-snapshot selector hook (ConvViewProps/ToolViewProps take this). */
 export type UseConversationSession = UseSession<ConversationSnapshot>
 
@@ -51,6 +54,25 @@ export type UseConversationSession = UseSession<ConversationSnapshot>
  */
 export type ToolCallBlock = RunningToolCall | ToolResultNode
 
+declare module '@deepseek-ai/dsh-client-ui-slots' {
+  /**
+   * Session standard kit, real members (ui-slots declares the empty seat;
+   * the runtime — where the subjects live — merges the concrete types):
+   * every session-scope slot component receives these from the framework.
+   */
+  interface SessionStandardProps {
+    /** Selector hook over this session's conversation snapshot. */
+    useSession: SnapshotSelectorHook<ConversationSnapshot>
+    /** The framework-resolved session id (owners never pass it). */
+    sessionId: SessionId
+  }
+  /** Global standard kit, real members: the session-list hook every slot component receives. */
+  interface GlobalStandardProps {
+    /** Selector hook over the session list snapshot (`current` included — the arbitrated selection seat). */
+    useSessions: SnapshotSelectorHook<SessionListState>
+  }
+}
+
 declare module 'cordis' {
   interface Events {
     /**