Merge remote-tracking branch 'origin/master' into worktree/web-session-titles

# Conflicts:
#	.agents/notes/implemented/process/2026-07-20-gui-testing-system.i18n.yaml
#	packages/client/ui-conversation/tests/apply-inject.spec.tsx
#	packages/client/ui-conversation/tests/chat-stats-bash-sample.spec.tsx
#	packages/client/ui-conversation/tests/gate-branch-tails.spec.tsx
#	packages/client/ui-conversation/tests/selection-survival.spec.ts
#	packages/client/ui-conversation/tests/skeleton-branches.spec.tsx
#	packages/client/ui-conversation/tests/skeleton.spec.tsx
#	packages/client/ui-layout/tests/service.spec.ts
#	packages/client/ui-sidebar/tests/apply.spec.tsx
#	packages/client/ui-sidebar/tests/store.spec.ts
#	packages/client/ui-trajectory/tests/views.spec.tsx
#	packages/client/web/src/app.tsx
#	packages/client/web/tests/boot.spec.tsx
#	packages/host/runtime/README.md
#	packages/host/runtime/tests/host-runtime.spec.ts

packages/client/runtime/src/client/contract/store.ts

@@ -0,0 +1,244 @@
+/**
+ * Snapshot store engine (zustand vanilla + immer + subscribeWithSelector +
+ * rafFlush middleware + opt-in persist + dev freeze) plus the declarative
+ * shell over it: {@link defineStore} bakes an init/persist/actions literal
+ * into a {@link StoreHandle}, the registration-side store seat of the slot
+ * terminal design (§4). Lives in the React-free runtime (store-migration
+ * ruling: the data layer owns its engine; web-react is shell-only React
+ * glue): engine products are bare observables — subscribe/getSnapshot/
+ * update/set, NO selector hook. Hook synthesis is web-react's (the one
+ * uSES bridge, cached per source at the binding site).
+ */
+import { createStore, type StoreApi } from 'zustand/vanilla'
+import { subscribeWithSelector } from 'zustand/middleware'
+import { shallow } from 'zustand/shallow'
+import { produce } from 'immer'
+import type {
+  ActionsDecl, BakedActions, StoreHandle, StoreInstance, StoreSpec,
+} from '@deepseek-ai/dsh-client-ui-slots'
+
+// Store contract types are ui-slots authority; re-exported beside the engine
+// so store consumers get one import surface.
+export type {
+  ActionsDecl, BakedActions, BoundActions, StoreFactory, StoreHandle, StoreInstance, StoreSpec,
+} from '@deepseek-ai/dsh-client-ui-slots'
+
+/** Minimal observable snapshot source: Session objects and snapshot stores both satisfy it. */
+export interface ObservableSnapshot<T> { getSnapshot(): T; subscribe(fn: () => void): () => void }
+
+/** Writable snapshot store (bare data face; React selector hooks are synthesized in web-react). */
+export interface SnapshotStore<T> extends ObservableSnapshot<T> {
+  /**
+   * Mutate the state through an immer draft.
+   * @param mutator - draft mutator.
+   */
+  update(mutator: (draft: T) => void): void
+  /**
+   * Replace the state wholesale.
+   * @param next - next state.
+   */
+  set(next: T): void
+}
+
+/**
+ * Shallow equality for selector slices (zustand/shallow semantics; travels
+ * with the engine so hook consumers need no zustand dependency).
+ * @param a - left value.
+ * @param b - right value.
+ * @returns whether the values are shallowly equal.
+ */
+export function shallowEqual(a: unknown, b: unknown): boolean {
+  return shallow(a, b)
+}
+
+/** Batches subscriber notification into one flush per animation frame. */
+function rafBatch(notify: () => void): () => void {
+  // Fall back to microtask batching where rAF is absent (node unit tests);
+  // both preserve the N-changes=1-notification contract within a tick.
+  const schedule: (fn: () => void) => void =
+    typeof requestAnimationFrame === 'function'
+      ? (fn) => { requestAnimationFrame(() => { fn() }) }
+      : (fn) => { queueMicrotask(fn) }
+  let scheduled = false
+  return () => {
+    if (scheduled) return
+    scheduled = true
+    schedule(() => {
+      scheduled = false
+      notify()
+    })
+  }
+}
+
+/**
+ * Create a snapshot store.
+ *
+ * Flush default is 'sync' (controlled inputs need same-tick echo); frame-driven
+ * stores opt into 'raf', where a frame's worth of updates coalesces into one
+ * notification. Known raf-mode tradeoff: a component mounting mid-frame reads
+ * fresh state while existing subscribers hear it next flush — transient
+ * frame-level skew, same nature as the object layer's microtask batching.
+ *
+ * @param init - initial state.
+ * @param opts - flush mode and opt-in persistence (localStorage, keyed by name).
+ * @returns the store.
+ */
+export function createSnapshotStore<T>(
+  init: T, opts?: { flush?: 'raf' | 'sync'; persist?: { name: string } }): SnapshotStore<T> {
+  // Immer enters through produce() in update() below (identical semantics to
+  // the immer middleware without its setState-signature mutator generics).
+  const withSelector = subscribeWithSelector(() => init)
+  const api: StoreApi<T> = createStore<T>()(withSelector)
+  if (opts?.persist) attachPersistence(api, opts.persist.name)
+
+  let subscribe = (fn: () => void) => api.subscribe(fn)
+  if (opts?.flush === 'raf') {
+    const listeners = new Set<() => void>()
+    const flush = rafBatch(() => { for (const fn of [...listeners]) fn() })
+    api.subscribe(flush)
+    subscribe = (fn: () => void) => {
+      listeners.add(fn)
+      return () => { listeners.delete(fn) }
+    }
+  }
+
+  return {
+    getSnapshot: () => api.getState(),
+    subscribe: fn => subscribe(fn),
+    update: (mutator) => {
+      // Immer's produce (not setState's partial-merge path) so scalar and
+      // array roots replace correctly; produce also freezes in dev.
+      api.setState(produce(api.getState(), (draft) => { mutator(draft as T) }), true)
+    },
+    set: (next) => {
+      api.setState(devFreeze(next), true)
+    },
+  }
+}
+
+/**
+ * Whole-value JSON persistence to localStorage. Hand-rolled instead of the
+ * zustand persist middleware: its write path spreads state into an object
+ * (`partialize({ ...get() })`), exploding primitive state (a persisted string
+ * draft becomes {0:'h',1:'e',...}) — not fixable via merge/deserialize options
+ * because the corruption happens before serialization. Storage failures
+ * (quota, private mode) only disable persistence, never break the store.
+ */
+function attachPersistence<T>(api: StoreApi<T>, name: string): void {
+  // Non-browser runs (node e2e booting the client tree) have no localStorage:
+  // persistence silently disables — same contract as a storage failure, minus
+  // the per-store console noise a ReferenceError would produce.
+  if (typeof localStorage === 'undefined') return
+  try {
+    const raw = localStorage.getItem(name)
+    if (raw !== null) {
+      api.setState(devFreeze(JSON.parse(raw) as T), true)
+    }
+  } catch (error) {
+    console.error(`snapshot store '${name}' rehydration failed:`, error)
+  }
+  api.subscribe((state) => {
+    try {
+      localStorage.setItem(name, JSON.stringify(state))
+    } catch (error) {
+      console.error(`snapshot store '${name}' persistence failed:`, error)
+    }
+  })
+}
+
+/** Deep-freeze wholesale-set state outside production: set() bypasses immer's freeze. */
+function devFreeze<T>(value: T): T {
+  if (process.env.NODE_ENV === 'production') return value
+  deepFreeze(value)
+  return value
+}
+
+function deepFreeze(value: unknown): void {
+  if (typeof value !== 'object' || value === null || Object.isFrozen(value)) return
+  Object.freeze(value)
+  for (const key of Reflect.ownKeys(value)) {
+    deepFreeze((value as Record<PropertyKey, unknown>)[key])
+  }
+}
+
+// ---- defineStore shell (slot terminal design §4) ----
+// The type authority is ui-slots' store family (create(scopeKey?) and
+// clearPersisted() included); this module houses only the engine-backed
+// implementation. The one engine-side widening left: instances expose the
+// raw engine store for framework/test surfaces.
+
+/** A live engine instance: the contract instance plus the raw engine store. */
+export interface EngineStoreInstance<T, A extends ActionsDecl<T>> extends StoreInstance<T, A> {
+  /** The underlying engine store (framework/test surface; components never see it). */
+  readonly store: SnapshotStore<T>
+}
+
+/** The engine-backed handle: create() narrowed to the engine instance. */
+export interface EngineStoreHandle<T, A extends ActionsDecl<T>> extends StoreHandle<T, A> {
+  /**
+   * Construct a live engine instance (see the contract JSDoc on
+   * {@link StoreHandle.create} for scopeKey/persist semantics).
+   *
+   * Known boundary: the persist key is the storage identity, so multiple live
+   * instances created under the same resolved key share (and cross-pollute)
+   * one localStorage entry. Instance uniqueness per key is the caller's
+   * responsibility — production is safe because the framework caches one
+   * instance per handle x scope key; tests wanting isolation use distinct
+   * scope keys or persist-free declarations (multi-create freedom is a
+   * feature there, so create() deliberately does not dedupe or throw).
+   * @param scopeKey - session id for session-scope instances; omitted for root scope.
+   * @returns the engine instance.
+   */
+  create(scopeKey?: string): EngineStoreInstance<T, A>
+}
+
+/**
+ * Declare a store: initial state, optional persistence, and the full write
+ * set as pure draft mutators. The returned handle is the registration
+ * currency of the store seat — its identity keys instance sharing. Satisfies
+ * ui-slots' DefineStore contract (the handle/instance are the engine-extended
+ * subtypes).
+ *
+ * The `A & ActionsDecl<T>` actions position is load-bearing: T resolves from
+ * `init` in the first inference round, and the intersection then contextually
+ * types each mutator's draft parameter (context-sensitive functions defer),
+ * so call sites write `(d, x: X) => { ... }` with no draft annotation. If a
+ * future TS version breaks this single-literal inference, the design's
+ * documented fallback is currying (`defineStore(init).actions({...})`).
+ * @param decl - init lambda (fresh state per instance), optional persist key, actions table.
+ * @returns the store handle.
+ */
+export function defineStore<T, A extends ActionsDecl<T>>(
+  decl: StoreSpec<T, A> & { actions: A & ActionsDecl<T> }): EngineStoreHandle<T, A> {
+  return {
+    spec: decl,
+    create(scopeKey?: string): EngineStoreInstance<T, A> {
+      const persistKey = decl.persist === undefined
+        ? undefined
+        : scopeKey === undefined ? decl.persist : `${decl.persist}.${scopeKey}`
+      const store = createSnapshotStore<T>(
+        decl.init(),
+        persistKey !== undefined ? { persist: { name: persistKey } } : undefined)
+      const actions = {} as Record<string, (...params: unknown[]) => void>
+      for (const key of Object.keys(decl.actions)) {
+        const mutate = decl.actions[key] as (draft: T, ...params: unknown[]) => void
+        actions[key] = (...params: unknown[]) => { store.update((draft) => { mutate(draft, ...params) }) }
+      }
+      return {
+        actions: actions as BakedActions<T, A>,
+        getSnapshot: () => store.getSnapshot(),
+        subscribe: fn => store.subscribe(fn),
+        store,
+        clearPersisted: () => {
+          if (persistKey === undefined || typeof localStorage === 'undefined') return
+          try {
+            localStorage.removeItem(persistKey)
+          } catch {
+            // Storage failures (private mode, quota teardown races) only skip
+            // cleanup — the same non-fatal contract as attachPersistence.
+          }
+        },
+      }
+    },
+  }
+}

packages/client/runtime/src/client/index.ts

@@ -1,30 +1,40 @@
 /**
  * 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 { SnapshotStore, UseSession } from '@deepseek-ai/dsh-client-web-react'
+import type { ConnectionHandle, SessionId } from '@deepseek-ai/dsh-client-connection/client'
+import type { SnapshotSelectorHook } from '@deepseek-ai/dsh-client-ui-slots'
+import type { SnapshotStore } from './contract/store.ts'
 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'
-export { SessionManager } from './sessions/manager.ts'
-export type { SessionListSnapshot } from './sessions/manager.ts'
-export { Session, PAGE_MESSAGES } from './sessions/session.ts'
-export type { SessionListEntry } from './sessions/lineage.ts'
+// The snapshot-store engine lives here since the store migration (the data
+// layer owns its substrate; web-react is React glue only). The './client'
+// main export is the single serving door — no store subpath.
+export { createSnapshotStore, defineStore, shallowEqual } from './contract/store.ts'
+export type {
+  EngineStoreHandle, EngineStoreInstance, ObservableSnapshot, SnapshotStore,
+} from './contract/store.ts'
 export type {
   AssistantBlock, AssistantMessageNode, ContextMessageNode, ConversationNode, ConversationSnapshot,
-  OpenState, PartialAssistant, PendingInteraction, PromptError, RunningToolCall, SteeringMessageNode,
+  PendingInteraction, RunningToolCall, SteeringMessageNode,
   ToolResultNode, UnknownSurfaceNode, UserMessageNode,
 } from './sessions/conversation.ts'
 export type { SessionId } from '@deepseek-ai/dsh-client-connection/client'
@@ -41,11 +51,8 @@ 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>
+/** The conversation-snapshot selector hook (ConvViewProps/ToolRowProps take this). */
+export type UseConversationSession = SnapshotSelectorHook<ConversationSnapshot>
 
 /**
  * One tool call as the chat flow renders it: still-running (spinner card) or
@@ -54,6 +61,25 @@ 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 {
     /**

packages/client/runtime/src/client/loader/index.ts

@@ -17,7 +17,7 @@
  * load one by one in inject topology.
  */
 import type { Context } from 'cordis'
-import { createSnapshotStore } from '@deepseek-ai/dsh-client-web-react'
+import { createSnapshotStore } from '../contract/store.ts'
 import type { BootPluginEntry, ClientLoader, LoaderStatus } from '../index.ts'
 
 export type { BootPluginEntry, ClientLoader, LoaderStatus } from '../index.ts'

packages/client/runtime/src/client/sessions/service.ts

@@ -1,20 +1,24 @@
 /**
  * SessionsService: root sessions service — list snapshot store (manager
- * projection), session scope tree (mintScope pattern: no-op plugin Fiber +
- * ctx.extend scope tag), stable SessionBinding cache, ancestry walk.
+ * projection; carries `current`, the persisted selection every
+ * session-scoped surface keys off — migrated here from ui-layout per the
+ * slot-parity design), session scope tree (mintScope pattern: no-op plugin
+ * Fiber + ctx.extend scope tag), stable SessionBinding cache, ancestry walk.
  *
- * Scope lifecycle is watch-driven: a scope is minted lazily on first
- * resolution; a session leaving the list tears its scope down only when
- * nobody is watching it. "Watched" is approximated as the most recently
- * resolved binding id — SessionProvider re-resolves on every selection
- * change (keyed remount), so a switch away always re-evaluates the deferred
- * teardown; a host-side death without list removal keeps the scope (frozen
- * read-only view).
+ * Scope lifecycle is stage-driven: a scope is minted lazily on first
+ * resolution (pure — resolution has no side effects and is render-safe);
+ * the event window and deferred teardown key off the STAGED session, which
+ * follows `list.current` exactly. Staging is the open signal: the window
+ * opens ⟺ the session is on stage (today the stage is `current`; the staged
+ * state can widen to a multi-pane list later). A session leaving the list
+ * tears its scope down immediately unless it is the staged one, whose scope
+ * survives frozen (read-only view) until the stage moves on.
  */
 import type { Context, Fiber } from 'cordis'
 import type { IApiClient, SessionId } from '@deepseek-ai/dsh-client-connection/client'
-import type { SnapshotStore } from '@deepseek-ai/dsh-client-web-react'
-import { createSnapshotStore } from '@deepseek-ai/dsh-client-web-react'
+import type { SessionCell } from '@deepseek-ai/dsh-client-ui-slots'
+import type { SnapshotStore } from '../contract/store.ts'
+import { createSnapshotStore } from '../contract/store.ts'
 import { SessionManager } from './manager.ts'
 import type { Session } from './session.ts'
 
@@ -31,8 +35,12 @@ export interface SessionSummary {
   updatedAt: number
 }
 
-/** Session list store shape. */
-export interface SessionListState { ids: SessionId[]; byId: Record<SessionId, SessionSummary> }
+/**
+ * Session list store shape. `current` rides the same snapshot (arbitrated:
+ * the single useSessions standard hook reads list and selection together —
+ * sidebar highlighting and SessionProvider share one fact source).
+ */
+export interface SessionListState { ids: SessionId[]; byId: Record<SessionId, SessionSummary>; current: SessionId | undefined }
 
 /** Session assembly handle for SessionProvider/inject factories (identity-stable per session). */
 export interface SessionBinding {
@@ -73,19 +81,35 @@ interface ScopeRecord {
   fiber: Fiber
   ctx: Context
   binding: SessionBinding
+  /** Render-layer standard kit (identity-stable per scope; the renderer's per-cell caches key off it). */
+  cell: SessionCell
 }
 
-/** Root sessions service: list store, object-layer manager, scope tree, bindings, ancestry. */
+/** Root sessions service: list store, current selection, object-layer manager, scope tree, bindings, ancestry. */
 export class SessionsService {
-  /** List snapshot store (list RPC + host stream increments; re-pulled on reconnect). */
+  /** List snapshot store (list RPC + host stream increments; re-pulled on reconnect) — the useSessions standard feed, current included. */
   readonly list: SnapshotStore<SessionListState>
   /** The object-layer instance cluster and frame dispatch entry (wired to the connection by the runtime apply). */
   readonly manager: SessionManager
 
+  /**
+   * Persisted selection cell (the durable half of `list.current`). Private on
+   * purpose: reads go through the list snapshot; writes through {@link
+   * SessionsService.open}. Projection validates it against the live list
+   * instead of destructively pruning, so a selection survives transient list
+   * states (reconnect re-pull) and resurfaces when its session returns.
+   */
+  private readonly selection: SnapshotStore<{ sessionId?: SessionId }>
+
   private readonly scopes = new Map<SessionId, ScopeRecord>()
-  /** Most recently resolved binding id — the watch approximation for deferred teardown. */
+  /**
+   * The staged session id — follows `list.current` exactly, holding its last
+   * defined value across masked gaps (a transiently absent selection blanks
+   * `current` without moving the stage, so reconnect re-pulls and removals
+   * keep the staged scope's frozen view alive until the stage moves on).
+   */
   private watched: SessionId | undefined
-  /** Removed-while-watched sessions whose teardown waits for the watch to move away. */
+  /** Removed-while-staged sessions whose teardown waits for the stage to move away. */
   private readonly deferredRemovals = new Set<SessionId>()
 
   /**
@@ -94,13 +118,36 @@ export class SessionsService {
    */
   constructor(private readonly rootCtx: Context, api: IApiClient) {
     this.manager = new SessionManager(api)
-    this.list = createSnapshotStore<SessionListState>({ ids: [], byId: {} })
+    this.selection = createSnapshotStore<{ sessionId?: SessionId }>(
+      {},
+      { persist: { name: 'dsh.sessions.current' } })
+    this.list = createSnapshotStore<SessionListState>({ ids: [], byId: {}, current: undefined })
     // The manager owns wire truth; the store is its projection. Manager
     // notifications are already microtask-batched.
     this.manager.subscribe(() => { this.projectList() })
+    // Stage follower: every current write (open() and projection alike)
+    // re-evaluates staging, so startup restore (persisted selection validated
+    // by the projection) and reconnect resurfacing open their window with no
+    // dedicated code path. Safe to run synchronously inside the store notify:
+    // the follower writes no list state — session.open()'s synchronous prefix
+    // touches only session-side state and its own microtask-batched notifier.
+    this.list.subscribe(() => { this.followCurrent() })
     rootCtx.reflect.provide('sessions', this, undefined)
   }
 
+  /**
+   * Select a session as current. Unknown ids fail loud instead of navigating
+   * nowhere (the sole selection write path).
+   * @param id - session id (must exist in the list store).
+   */
+  open(id: SessionId): void {
+    if (this.list.getSnapshot().byId[id] === undefined) {
+      throw new Error(`sessions.open: unknown session ${id}`)
+    }
+    this.selection.update((draft) => { draft.sessionId = id })
+    this.list.update((draft) => { draft.current = id })
+  }
+
   /**
    * Create a session on the host.
    * @param opts - creation options (project directory).
@@ -122,18 +169,50 @@ export class SessionsService {
   }
 
   /**
-   * Resolve the stable session binding (SessionProvider's resolveBinding feed).
+   * Resolve the stable session binding (scope-addressed assembly feed). Pure
+   * resolution — no staging, no window side effects.
    * @param id - session id.
    * @returns binding, or undefined for a session neither listed nor already scoped.
    */
   binding(id: SessionId): SessionBinding | undefined {
-    const record = this.resolve(id)
-    if (record === undefined) return undefined
-    if (this.watched !== id) {
-      this.watched = id
-      this.sweepDeferred()
+    return this.resolve(id)?.binding
+  }
+
+  /**
+   * Resolve the render-layer session cell (SessionProvider's feed through
+   * the renderer host; ctx never enters the render layer). Pure resolution —
+   * render-safe: SessionProvider calls this during render, so no staging, no
+   * window side effects (StrictMode double-invokes and concurrent discarded
+   * passes must stay free).
+   * @param id - session id.
+   * @returns cell, or undefined for a session neither listed nor already scoped.
+   */
+  cell(id: string): SessionCell | undefined {
+    return this.resolve(id as SessionId)?.cell
+  }
+
+  /**
+   * Move the stage to the list's current session: sweep teardowns deferred
+   * behind the previous occupant and pull the new occupant's history window.
+   * Staging IS the open signal — the window opens ⟺ the session is on stage
+   * — and open() is idempotent (an in-flight or completed open no-ops; a
+   * failed one retries the next time current is touched).
+   */
+  private followCurrent(): void {
+    const current = this.list.getSnapshot().current
+    // A masked gap (current blanked while the selection's session is
+    // transiently absent) holds the stage: tearing down on the gap would
+    // destroy exactly the frozen scope the mask exists to preserve.
+    if (current === undefined || current === this.watched) return
+    this.watched = current
+    this.sweepDeferred()
+    const record = this.resolve(current)
+    /* v8 ignore next 3 -- defensive: current is always a listed id (open()
+     * validates and the projection masks absent selections), so resolve
+     * cannot miss; kept so a future current writer cannot crash the notify. */
+    if (record !== undefined) {
+      void record.binding.session.open()
     }
-    return record.binding
   }
 
   /**
@@ -162,10 +241,14 @@ export class SessionsService {
     if (this.list.getSnapshot().byId[id] === undefined) return undefined
     const fiber = this.rootCtx.plugin(sessionScope)
     const ctx = fiber.ctx.extend({ [kScope]: id })
+    const session = this.manager.get(id)
     const record: ScopeRecord = {
       fiber,
       ctx,
-      binding: { sessionId: id, session: this.manager.get(id), ctx },
+      binding: { sessionId: id, session, ctx },
+      // Bare source form (store migration): the Session object IS the
+      // observable; the React side binds the useSession hook per cell.
+      cell: { sessionId: id, session },
     }
     this.scopes.set(id, record)
     return record
@@ -188,11 +271,15 @@ export class SessionsService {
         ...(entry.parentSessionId !== undefined ? { parentId: entry.parentSessionId } : {}),
       }
     }
-    this.list.set({ ids, byId })
+    // current = the persisted selection, masked while its session is absent
+    // (falls to the empty state; resurfaces if the session returns).
+    const selected = this.selection.getSnapshot().sessionId
+    const current = selected !== undefined && byId[selected] !== undefined ? selected : undefined
+    this.list.set({ ids, byId, current })
     this.pruneScopes(byId)
   }
 
-  /** Tear down scopes for removed sessions nobody watches; the watched one defers until the watch moves. */
+  /** Tear down scopes for removed sessions off stage; the staged one defers until the stage moves. */
   private pruneScopes(byId: Record<SessionId, SessionSummary>): void {
     for (const [id, record] of this.scopes) {
       if (byId[id] !== undefined) continue
@@ -202,15 +289,23 @@ export class SessionsService {
       }
       this.scopes.delete(id)
       this.deferredRemovals.delete(id)
-      void record.fiber.dispose()
+      this.dropScope(id, record)
     }
   }
 
-  /** Run deferred teardowns whose session is no longer watched (called when the watch moves). */
+  /** Dispose a scope fiber and its session-keyed slot-store instances together (single lifecycle axis). */
+  private dropScope(id: SessionId, record: ScopeRecord): void {
+    void record.fiber.dispose()
+    // Optional lookup: slots and sessions are sibling services with no
+    // declared dependency; a slots-less boot (object-layer tests) skips.
+    this.rootCtx.get('slots')?.pruneStoreScope(id)
+  }
+
+  /** Run deferred teardowns whose session is no longer staged (called when the stage moves). */
   private sweepDeferred(): void {
     for (const id of [...this.deferredRemovals]) {
-      /* v8 ignore next -- defensive: only the watched id ever defers, and every
-       * watch move sweeps first, so the set cannot contain the id the watch just
+      /* v8 ignore next -- defensive: only the staged id ever defers, and every
+       * stage move sweeps first, so the set cannot contain the id the stage just
        * moved to; kept as a guard against future extra sweep call sites. */
       if (id === this.watched) continue
       // Still absent from the list? (A re-added id cancels the deferred teardown.)
@@ -225,7 +320,7 @@ export class SessionsService {
        * future teardown path cannot double-dispose. */
       if (record !== undefined) {
         this.scopes.delete(id)
-        void record.fiber.dispose()
+        this.dropScope(id, record)
       }
     }
   }

packages/client/runtime/src/client/sessions/session.ts

@@ -7,8 +7,7 @@ import type { ContentBlock } from '@deepseek-ai/dsh-llm/types'
 import type { SessionEvent } from '@deepseek-ai/dsh-session/types'
 import type { HistoryEntry, IApiClient, MuxFrame, RpcError, RpcId, RpcResult, SessionId, ToolEventView } from '@deepseek-ai/dsh-client-connection/client'
 import { transportError } from '@deepseek-ai/dsh-client-connection/client'
-import type { ObservableSnapshot, SnapshotSelectorHook } from '@deepseek-ai/dsh-client-web-react'
-import { bindSnapshotSelector } from '@deepseek-ai/dsh-client-web-react'
+import type { ObservableSnapshot } from '../contract/store.ts'
 import type {
   ConversationNode, ConversationSnapshot, OpenState, PendingInteraction, PromptError, RunningToolCall,
 } from './conversation.ts'
@@ -19,11 +18,13 @@ import { PartialAccumulator } from './partial.ts'
 /** Messages per page (F.4 ledger: promote to Config at graduation; every call site references this constant). */
 export const PAGE_MESSAGES = 50
 
-/** Per-session state owner: event window + fold + partial, snapshot out via uSES (see the web client architecture RFC). */
+/**
+ * Per-session state owner: event window + fold + partial, snapshot out via
+ * subscribe/getSnapshot (see the web client architecture RFC). Bare source
+ * only (store migration): the React machinery binds the per-cell useSession
+ * hook at its own seam — no selector hook member lives on the data layer.
+ */
 export class Session implements ObservableSnapshot<ConversationSnapshot> {
-  /** Typed selector hook bound to this instance (the SessionBinding `useSession` source). */
-  readonly useSelector: SnapshotSelectorHook<ConversationSnapshot> = bindSnapshotSelector(this)
-
   // ---- Window and derived state (all private; the snapshot is the only read surface) ----
   private events: SessionEvent[] = []
   /** Wire views aligned with `events` by index (envelope-level annotations; undefined = no view).

packages/client/runtime/src/client/slots.ts

@@ -1,22 +1,84 @@
 /**
- * SlotsService: cordis Service wrapper over the pure SlotCore (ui-slots).
- * Every mutation re-emits as the 'slots/changed' cordis event; define/register
- * run through the caller's ctx.effect so a plugin's registrations are
- * collected when its fiber unloads (cordis-native cascade).
+ * SlotsService: the cordis Service layer of the slot system over the pure
+ * SlotCore (ui-slots owns registration semantics, the declaration ledger,
+ * the load-time validations, and the unload cascade). This layer owns what
+ * needs the runtime: the 'slots/changed' event bridge, register through the
+ * caller's ctx.effect (fiber unload collects registrations), the renderer
+ * install seam (install()/renderSlot('root') + the SlotRendererHost face),
+ * and the store INSTANCE axis — handle x scope key -> create/cache, dropped
+ * with the last holding entry, session instances cleared (with persisted
+ * state) on scope death.
  */
 /* eslint-disable @typescript-eslint/no-redundant-type-constituents --
- * `keyof SlotMap & string` is the declare-merge key pattern: SlotMap is empty
- * in this compilation unit (intersection reads `never`) but consumers merge
- * keys in; the rule fires on the empty-map view, not on real redundancy. */
+ * `keyof SlotMap & string` is the declare-merge key pattern: SlotMap only
+ * holds this package's 'root' row in this compilation unit, but consumers
+ * merge keys in; the rule fires on the narrow-map view, not on real
+ * redundancy. */
 import { Service } from 'cordis'
 import type { Context } from 'cordis'
 import { SlotCore } from '@deepseek-ai/dsh-client-ui-slots'
-import type { ComposedProps, RegisterArgs, SlotComponent, SlotEntry, SlotEntryDef, SlotMap, SlotSpec } from '@deepseek-ai/dsh-client-ui-slots'
-import type { ClientContext } from './index.ts'
+import type {
+  OwnerOf, SlotEntryDef, SlotMap, SlotRenderer, SlotRendererHost,
+  SlotScope, SlotSpec, StoreDecl, StoredEntry, StoreInstanceLike,
+} from '@deepseek-ai/dsh-client-ui-slots'
 
-/** cordis Service wrapper over the pure SlotCore; mutations re-emit as 'slots/changed'. */
+declare module '@deepseek-ai/dsh-client-ui-slots' {
+  interface SlotMap {
+    /** The built-in render-tree root hole (seeded by SlotCore): rendered only by the shell, occupied by a layout entry. */
+    'root': { kind: 'single'; scope: 'root'; owner: RootOwnerProps }
+  }
+}
+
+/** Root owner share: the shell supplies nothing — the frame is inject-assembled. */
+export interface RootOwnerProps { children?: never }
+
+/** Instance key for root-scoped store records (session records key by session id, so the literal cannot collide). */
+const ROOT_INSTANCE_KEY = 'root'
+
+// FIXME(slot-parity): the engine's arbitrated persist extensions — create()
+// takes the scope key (per-session localStorage suffix) and instances expose
+// clearPersisted() — are not yet on ui-slots' StoreHandle/StoreInstanceLike;
+// these local structural faces bridge until fw-slots lifts them.
+
+/** Store handle face as the engine actually ships it (scope-key-aware create). */
+interface EngineStoreHandle { create(scopeKey?: string): EngineStoreInstance }
+
+/** Engine instance face: the host-contract shape plus persisted-state cleanup. */
+interface EngineStoreInstance extends StoreInstanceLike { clearPersisted(): void }
+
+/** Store axis record: one per live handle, dropped when the last holding entry unloads. */
+interface StoreAxisRecord {
+  /** Scope of the slot the handle mounted under (the core validated cross-scope conflicts). */
+  scope: SlotScope
+  /** Live registrations holding the handle. */
+  refs: number
+  /** Root scope: the single instance under {@link ROOT_INSTANCE_KEY}; session scope: one per session id. */
+  instances: Map<string, EngineStoreInstance>
+}
+
+/** Type-erased options view the implementation works with (the typed overloads proved the shares). */
+interface ErasedRegisterOptions {
+  name: string
+  children?: Record<string, SlotSpec<SlotEntryDef>>
+  store?: StoreDecl
+  inject?: (...args: never[]) => Record<string, unknown>
+  key?: string
+  id?: string
+  order?: number
+  label?: string
+  registrant?: string
+}
+
+/** Erased core call face (the service re-erases at its own boundary; the core's typed face targets end callers). */
+interface ErasedCore { register(options: object, component: unknown): () => void }
+
+/** cordis Service layer of the slot system; see the module doc for the split with SlotCore. */
 export class SlotsService extends Service {
   private readonly _core = new SlotCore()
+  /** Store-instance axis: handle -> mounted scope, refcount, resolved instances. */
+  private readonly _stores = new Map<EngineStoreHandle, StoreAxisRecord>()
+  private _renderer: SlotRenderer | undefined
+  private _host: SlotRendererHost | undefined
 
   /**
    * @param ctx - owning root context.
@@ -27,44 +89,92 @@ export class SlotsService extends Service {
   }
 
   /**
-   * Record a slot spec (delegates to SlotCore.define; disposal follows the caller's fiber).
-   * @param key - SlotMap key.
-   * @param spec - kind/scope spec.
-   * @returns disposer.
+   * The single registration API. The typed face IS the core's register
+   * (both overloads reused verbatim — one authority, no structural copy;
+   * see SlotCore.register for children declaration, store seat, inject
+   * face, load-time validation, and the unload cascade). This layer adds:
+   * disposal through the caller's ctx.effect (fiber unload = cascade),
+   * exclusive-factory minting (`store: createXxxStore` becomes a per-entry
+   * handle), the registrant diagnostics stamp, and store-instance lifecycle
+   * on the entry axis.
+   *
+   * Declared here, implemented by prototype assignment below the class: it
+   * MUST stay a prototype method (never an instance arrow) — the cordis
+   * service proxy binds `this.ctx` to the CALLER's context at call time,
+   * which is what routes the effect (and the unload cascade) into the
+   * caller's fiber. An arrow property would freeze `this` to the service's
+   * own root ctx and silently break per-plugin disposal.
    */
-  define<K extends keyof SlotMap & string>(key: K, spec: SlotSpec<SlotMap[K]>): () => void {
-    // eslint-disable-next-line @typescript-eslint/no-misused-promises -- synchronous cleanup; direct return preserves disposer identity
-    return this.ctx.effect(() => this._core.define(key, spec), 'slots.define()')
+  declare readonly register: SlotCore['register']
+
+  /**
+   * Install the shell's renderer (web-react's createSlotRenderer product).
+   * Boot-once: a second install throws. Runs through the caller's ctx.effect,
+   * so shell fiber unload uninstalls the renderer.
+   * @param renderer - the outlet machinery implementing SlotRenderer.
+   */
+  install(renderer: SlotRenderer): void {
+    if (this._renderer !== undefined) throw new Error('slot renderer already installed (install() is boot-once)')
+    this.ctx.effect(() => {
+      this._renderer = renderer
+      return () => {
+        if (this._renderer === renderer) this._renderer = undefined
+      }
+    }, 'slots.install()')
   }
 
   /**
-   * Contribute a component (delegates to SlotCore.register; disposal follows the caller's fiber).
-   * @param key - SlotMap key.
-   * @param component - contributed component.
-   * @param args - kind-shaped options (mandatory for keyed/list kinds); the
-   * inject factory's binding is pinned to ClientContext.
-   * @returns disposer.
+   * The single ctx-level render entry: the shell renders 'root'; every other
+   * key renders inside components through the props renderSlot face. All
+   * three guards are fail-loud boot-order checks, no fallback.
+   * @param key - must be 'root' (runtime-enforced for dynamically composed callers).
+   * @param owner - owner share for the root entry (the shell supplies {}).
+   * @returns the rendered root tree.
    */
-  register<K extends keyof SlotMap & string, I extends object = Record<string, unknown>>(
-    // Client-context registrations have exactly one ctx shape: pin Ctx to
-    // ClientContext so inject factories dot services without a cast.
-    key: K, component: SlotComponent<ComposedProps<K, NoInfer<I>>>,
-    ...args: RegisterArgs<SlotMap[K], I, ClientContext>): () => void {
-    // eslint-disable-next-line @typescript-eslint/no-misused-promises -- synchronous cleanup; direct return preserves disposer identity
-    return this.ctx.effect(() => this._core.register<K, I, ClientContext>(key, component, ...args), 'slots.register()')
+  renderSlot<K extends keyof SlotMap & string>(key: K, owner: OwnerOf<K>): ReturnType<SlotRenderer['renderRoot']> {
+    // Widened: in this package's own program SlotMap holds only 'root', which
+    // would fold the guard to constant-false; the check exists for plain-JS
+    // and cross-program callers where K is wider.
+    if ((key as string) !== 'root') {
+      throw new Error(`ctx-level renderSlot only renders 'root' (got "${key}"); child slots render through the component props face`)
+    }
+    if (this._renderer === undefined) {
+      throw new Error("slot renderer not installed — boot must call ctx.slots.install(createSlotRenderer()) before rendering 'root'")
+    }
+    if (this._core.entries('root').length === 0) {
+      throw new Error("'root' has no registration — a layout entry must register into 'root' before the shell renders it")
+    }
+    return this._renderer.renderRoot(this.hostFace(), owner)
   }
 
   /**
-   * Snapshot entries for a key.
-   * @param key - SlotMap key.
-   * @returns registered entries (stable reference between mutations).
+   * Drop the per-session store instances of a dead session (the sessions
+   * service calls this on scope teardown; root-scoped records are untouched).
+   * Persisted state goes with the session — a never-rendered dead session can
+   * still own keys from an earlier page load, so the instance is materialized
+   * transiently just to clear storage (no-op for unpersisted stores).
+   * @param sessionId - the torn-down session.
    */
-  entries<K extends keyof SlotMap & string>(key: K): readonly SlotEntry<SlotMap[K]>[] {
+  pruneStoreScope(sessionId: string): void {
+    for (const [handle, record] of this._stores) {
+      if (record.scope !== 'session') continue
+      const instance = record.instances.get(sessionId) ?? handle.create(sessionId)
+      instance.clearPersisted()
+      record.instances.delete(sessionId)
+    }
+  }
+
+  /**
+   * Snapshot entries for a key (render-erased view; stable reference between mutations).
+   * @param key - SlotMap key.
+   * @returns registered entries.
+   */
+  entries(key: keyof SlotMap & string): readonly StoredEntry[] {
     return this._core.entries(key)
   }
 
   /**
-   * Look up a defined spec.
+   * Look up a declared spec (register-declared or the built-in 'root').
    * @param key - SlotMap key.
    * @returns spec or undefined.
    */
@@ -72,15 +182,6 @@ export class SlotsService extends Service {
     return this._core.spec(key)
   }
 
-  /**
-   * Dynamic-key escape hatch for spec lookup (renderer-side string keys).
-   * @param key - candidate slot key.
-   * @returns wide-typed spec or undefined.
-   */
-  specDynamic(key: string): SlotSpec<SlotEntryDef> | undefined {
-    return this._core.specDynamic(key)
-  }
-
   /**
    * Subscribe to a key's registration changes (microtask-batched).
    * @param key - SlotMap key.
@@ -100,8 +201,114 @@ export class SlotsService extends Service {
     return this._core.getVersion(key)
   }
 
-  /** The wrapped pure core (web-react's scopedSlots outlet reads through this). */
-  get core(): SlotCore {
-    return this._core
+  /** Delegating registration path: factory minting + registrant stamp + core write + instance-axis bookkeeping. */
+  private _register(options: ErasedRegisterOptions, component: unknown): () => void {
+    // Exclusive stores pass the factory itself: minted here into a per-entry
+    // handle so the stored entry always carries a resolvable handle (the
+    // core's shared-handle scope pinning applies to it harmlessly).
+    const store = typeof options.store === 'function' ? options.store() : options.store
+    const registrant = options.registrant ?? (this.ctx.fiber as { name?: string } | undefined)?.name
+    const erased: ErasedRegisterOptions = {
+      ...options,
+      ...(store !== undefined ? { store } : {}),
+      ...(registrant !== undefined ? { registrant } : {}),
+    }
+    // Core write first: all load-time validation (undeclared target,
+    // duplicate declaration, kind conflicts, cross-scope handle) throws
+    // there before this layer commits anything.
+    const dispose = (this._core as unknown as ErasedCore).register(erased, component)
+    if (store !== undefined) {
+      // Register succeeded, so the target's spec is on the ledger.
+      const scope = (this._core.specDynamic(options.name) as SlotSpec<never>).scope
+      this._acquire(store, scope)
+    }
+    let disposed = false
+    return () => {
+      if (disposed) return
+      disposed = true
+      dispose()
+      if (store !== undefined) this._release(store)
+    }
+  }
+
+  /** Build (once) the host face the installed renderer reads; sessions resolve lazily at first render. */
+  private hostFace(): SlotRendererHost {
+    if (this._host !== undefined) return this._host
+    const sessions = this.ctx.get('sessions')
+    if (sessions === undefined) {
+      throw new Error("renderSlot('root') before the sessions service mounted — boot order puts runtime apply first")
+    }
+    // Identity-stable view: current rides the list snapshot (arbitrated), but
+    // the provider consumes it as its own observable; one cached object keeps
+    // the renderer's per-source hook cache stable.
+    const current = {
+      getSnapshot: () => sessions.list.getSnapshot().current as string | undefined,
+      subscribe: (fn: () => void) => sessions.list.subscribe(fn),
+    }
+    this._host = {
+      subscribe: (key, fn) => this._core.subscribe(key, fn),
+      getVersion: key => this._core.getVersion(key),
+      entriesOf: key => this._core.entries(key),
+      specOf: key => this._core.specDynamic(key),
+      isLive: entry => this._core.isLive(entry),
+      storeOf: (entry, scopeKey) =>
+        entry.store === undefined ? undefined : this.resolveStore(entry.store as unknown as EngineStoreHandle, scopeKey),
+      sessions: {
+        list: sessions.list,
+        current,
+        cell: id => sessions.cell(id),
+      },
+    }
+    return this._host
+  }
+
+  /** Resolve (create or reuse) the store instance for a registered handle under a scope key. */
+  private resolveStore(handle: EngineStoreHandle, sessionId: string | undefined): StoreInstanceLike {
+    const record = this._stores.get(handle)
+    if (record === undefined) throw new Error('store handle is not registered (entry unloaded, or the handle never went through register)')
+    const key = record.scope === 'session' ? sessionId : ROOT_INSTANCE_KEY
+    if (key === undefined) throw new Error('session-scoped store resolution requires a session id')
+    let instance = record.instances.get(key)
+    if (instance === undefined) {
+      // Session instances get the scope key (the engine suffixes the persist
+      // key per session); root instances stay keyless.
+      instance = record.scope === 'session' ? handle.create(key) : handle.create()
+      record.instances.set(key, instance)
+    }
+    return instance
+  }
+
+  /** Bind (or re-reference) a handle on the axis; cross-scope conflicts already threw in the core. */
+  private _acquire(handle: EngineStoreHandle, scope: SlotScope): void {
+    const record = this._stores.get(handle)
+    if (record === undefined) {
+      this._stores.set(handle, { scope, refs: 1, instances: new Map() })
+      return
+    }
+    record.refs += 1
+  }
+
+  /** Drop one reference; the last holder's unload drops the record (instances go with it — engine stores need no explicit dispose). */
+  private _release(handle: EngineStoreHandle): void {
+    const record = this._stores.get(handle)
+    /* v8 ignore next -- defensive: release only runs from a disposer whose
+     * register acquired the same handle, so the record must exist; kept so a
+     * future call site cannot underflow the axis. */
+    if (record === undefined) return
+    record.refs -= 1
+    if (record.refs === 0) this._stores.delete(handle)
   }
 }
+
+// register's implementation (prototype assignment pairs with the `declare`
+// inside the class — see its JSDoc for why it must live on the prototype).
+// Element access reaches the private _register legally and keeps it a
+// TS-visible read.
+;(SlotsService.prototype as { register: (options: object, component: unknown) => () => void }).register
+  = function register(this: SlotsService, rawOptions: object, component: unknown): () => void {
+    // The core's overloads proved the shares; the implementation works on
+    // the erased view (same pattern as the core's own implementation arm).
+    const options = rawOptions as ErasedRegisterOptions
+    // eslint-disable-next-line @typescript-eslint/no-misused-promises -- synchronous cleanup; direct return preserves disposer identity
+    return this.ctx.effect(() => this['_register'](options, component), 'slots.register()')
+  }

packages/client/runtime/src/env.d.ts

@@ -0,0 +1,5 @@
+/**
+ * Bundler-replaced NODE_ENV: vite/tsdown substitute the literal, so browsers
+ * never evaluate a bare `process`. tsconfig carries no node types on purpose.
+ */
+declare const process: { env: { NODE_ENV?: string } }