fix(client): publish current session provide bundle as one reactive projection

A provider roster change under a stable current id rematerialized every
scope's bundle but nothing notified React: SessionProvider resolved the
bundle from a current-id subscription only, so mounted entries kept the
obsolete hook/prop schema until an unrelated re-render. The sessions
service now owns an atomic currentProvide observable fed by both current
writes and roster changes; the renderer host exposes it as
sessions.provide, replacing the current/provideInfo/maybeProvideInfo
trio, and both providers subscribe to it.

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

@@ -151,6 +151,13 @@ export class SessionsService {
   readonly list: SnapshotStore<SessionListState>
   /** The object-layer instance cluster and frame dispatch entry. */
   private readonly manager: SessionManager
+  /**
+   * Atomic current-session provide projection: selection changes and
+   * provider-roster changes publish through this one source (the renderer
+   * host's `sessions.provide` feed), so a roster change under a stable
+   * current id republishes the bundle instead of stranding mounted entries.
+   */
+  readonly currentProvide: HostObservable<SessionMaybeProvideInfo>
 
   /**
    * Persisted selection cell (the durable half of `list.current`). Private on
@@ -167,6 +174,10 @@ export class SessionsService {
   private readonly providers: SessionProvideDescriptor[] = []
   /** Static no-session projection, rebuilt only when the provider roster changes. */
   private maybeInfo: SessionMaybeProvideInfo
+  /** Latest published {@link SessionsService.currentProvide} bundle (identity comparison dedupes republish). */
+  private currentProvideSnapshot: SessionMaybeProvideInfo
+  /** currentProvide subscribers (plain cell: bundles hold live Session sources, so no store freeze may touch them). */
+  private readonly currentProvideListeners = new Set<() => void>()
   /**
    * The staged session id — follows `list.current` exactly, holding its last
    * defined value across masked gaps (a transiently absent selection blanks
@@ -198,7 +209,11 @@ export class SessionsService {
     // 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() })
+    // The current-provide projection follows the same current writes.
+    this.list.subscribe(() => {
+      this.followCurrent()
+      this.projectCurrentProvide()
+    })
     // The runtime's own contribution comes first: useSession rides the same
     // provide channel every plugin uses (no renderer special case).
     this.providers.push({
@@ -206,6 +221,14 @@ export class SessionsService {
       resolve: binding => ({ hooks: { session: binding.session } }),
     })
     this.maybeInfo = this.materializeMaybeProvideInfo()
+    this.currentProvideSnapshot = this.maybeInfo
+    this.currentProvide = {
+      getSnapshot: () => this.currentProvideSnapshot,
+      subscribe: (fn) => {
+        this.currentProvideListeners.add(fn)
+        return () => { this.currentProvideListeners.delete(fn) }
+      },
+    }
     rootCtx.reflect.provide('sessions', this, undefined)
   }
 
@@ -238,6 +261,20 @@ export class SessionsService {
     for (const record of this.scopes.values()) {
       record.provideInfo = this.materializeProvideInfo(record.binding)
     }
+    this.projectCurrentProvide()
+  }
+
+  /**
+   * Publish the current selection's provide bundle when it changed. Bundles
+   * are identity-stable per (scope, roster) materialization, so an identity
+   * compare is exact; synchronous notify — both call sites (list.subscribe,
+   * provide()) already sit behind their own batching or registration edges.
+   */
+  private projectCurrentProvide(): void {
+    const next = this.maybeProvideInfo(this.list.getSnapshot().current)
+    if (next === this.currentProvideSnapshot) return
+    this.currentProvideSnapshot = next
+    for (const fn of [...this.currentProvideListeners]) fn()
   }
 
   /** Build the static no-session kit and reject duplicate declared names. */
@@ -404,11 +441,11 @@ export class SessionsService {
   }
 
   /**
-   * Resolve the render-layer standard-props bundle (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).
+   * Resolve one session's render-layer standard-props bundle (ctx never
+   * enters the render layer; the renderer subscribes to
+   * {@link SessionsService.currentProvide}). Pure resolution — render-safe:
+   * no staging, no window side effects (StrictMode double-invokes and
+   * concurrent discarded passes must stay free).
    * @param id - session id.
    * @returns the provide info, or undefined for a session neither listed nor already scoped.
    */

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

@@ -246,13 +246,6 @@ export class SlotsService extends Service {
     if (workspaces === undefined) {
       throw new Error("renderSlot('root') before the workspaces 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),
@@ -263,9 +256,7 @@ export class SlotsService extends Service {
         entry.store === undefined ? undefined : this.resolveStore(entry.store as unknown as EngineStoreHandle, scopeKey),
       sessions: {
         list: sessions.list,
-        current,
-        provideInfo: id => sessions.provideInfo(id),
-        maybeProvideInfo: id => sessions.maybeProvideInfo(id),
+        provide: sessions.currentProvide,
       },
       workspaces: { list: workspaces.list },
     }

packages/client/runtime/tests/sessions-service.spec.ts

@@ -195,6 +195,60 @@ describe('cell (render-layer session kit)', () => {
     expect(b.svc.provideInfo('ghost')).toBeUndefined()
   })
 
+  it('currentProvide follows selection: absent projection ↔ definite bundle, notified on each move', async () => {
+    const b = bench()
+    await feedList(b, [{ id: 's1' }, { id: 's2' }])
+    const absent = b.svc.currentProvide.getSnapshot()
+    expect(absent.sessionId).toBeUndefined()
+    expect(Object.hasOwn(absent.hooks, 'session')).toBe(true)
+    const notified = vi.fn()
+    b.svc.currentProvide.subscribe(notified)
+    b.svc.open(sid('s1'))
+    expect(b.svc.currentProvide.getSnapshot()).toBe(b.svc.provideInfo('s1'))
+    expect(notified).toHaveBeenCalledTimes(1)
+    b.svc.open(sid('s2'))
+    expect(b.svc.currentProvide.getSnapshot()).toBe(b.svc.provideInfo('s2'))
+    expect(notified).toHaveBeenCalledTimes(2)
+    b.svc.clear()
+    await Promise.resolve() // clearSelection projects through the manager notifier
+    expect(b.svc.currentProvide.getSnapshot().sessionId).toBeUndefined()
+  })
+
+  it('a provider roster change under a stable current id republishes the bundle', async () => {
+    const b = bench()
+    await feedList(b, [{ id: 's1' }])
+    b.svc.open(sid('s1'))
+    const before = b.svc.currentProvide.getSnapshot()
+    const notified = vi.fn()
+    b.svc.currentProvide.subscribe(notified)
+    const source = { getSnapshot: () => 'live', subscribe: () => () => {} }
+    const dispose = b.svc.provide({
+      hooks: ['extra'],
+      props: ['marker'],
+      resolve: () => ({ hooks: { extra: source }, props: { marker: 7 } }),
+    })
+    const added = b.svc.currentProvide.getSnapshot()
+    expect(added).not.toBe(before)
+    expect(added).toMatchObject({ sessionId: 's1', props: { marker: 7 } })
+    expect(added.hooks['extra']).toBe(source)
+    expect(notified).toHaveBeenCalledTimes(1)
+    dispose()
+    const removed = b.svc.currentProvide.getSnapshot()
+    expect(removed).not.toBe(added)
+    expect(Object.hasOwn(removed.hooks, 'extra')).toBe(false)
+    expect(notified).toHaveBeenCalledTimes(2)
+  })
+
+  it('an unsubscribed currentProvide listener stops receiving notifications', async () => {
+    const b = bench()
+    await feedList(b, [{ id: 's1' }])
+    const notified = vi.fn()
+    const off = b.svc.currentProvide.subscribe(notified)
+    off()
+    b.svc.open(sid('s1'))
+    expect(notified).not.toHaveBeenCalled()
+  })
+
   it('provideInfo()/binding() are pure resolution: no staging, no deferred sweep', async () => {
     const b = bench()
     await feedList(b, [{ id: 's1' }, { id: 's2' }])

packages/client/runtime/tests/slots-service.spec.ts

@@ -97,18 +97,13 @@ function fakeWorkspaces() {
   return { list: { getSnapshot: () => state, subscribe: () => () => undefined } }
 }
 
-/** Minimal sessions face for the host seam (list observable + provide bundle). */
+/** Minimal sessions face for the host seam (list observable + current provide projection). */
 function fakeSessions() {
   const state = { ids: [], byId: {}, current: undefined as string | undefined }
+  const absentInfo = { sessionId: undefined, hooks: { session: undefined }, props: {} }
   return {
     list: { getSnapshot: () => state, subscribe: () => () => undefined },
-    provideInfo: (id: string) => (id === 'known'
-      ? {
-        sessionId: id,
-        hooks: { session: { getSnapshot: () => undefined, subscribe: () => () => undefined } },
-        props: {},
-      }
-      : undefined),
+    currentProvide: { getSnapshot: () => absentInfo, subscribe: () => () => undefined },
   }
 }
 
@@ -232,13 +227,11 @@ describe('host face', () => {
     expect(host.entriesOf('t.host')).toHaveLength(0)
   })
 
-  it('exposes sessions list/current/provideInfo (current riding the list snapshot)', async () => {
+  it('exposes the session list and the atomic current provide projection', async () => {
     const bench = await boot()
     const host = captureHost(bench)
     expect(host.sessions.list.getSnapshot()).toMatchObject({ ids: [] })
-    expect(host.sessions.current.getSnapshot()).toBeUndefined()
-    expect(host.sessions.provideInfo('known')).toMatchObject({ sessionId: 'known' })
-    expect(host.sessions.provideInfo('ghost')).toBeUndefined()
+    expect(host.sessions.provide.getSnapshot()).toMatchObject({ sessionId: undefined })
   })
 
   it('exposes the independent Workspace list source', async () => {