fix(web): fence plan mode projection races

packages/client/runtime/README.md

@@ -8,7 +8,7 @@ Client cordis boot + core services: SlotsService (Service wrapper over SlotCore
 
 ## Plan-mode projection
 
-Each opened `Session` queries the optional plan capability independently of paginated history and exposes `planMode: null | { active, pending? }` in its `ConversationSnapshot`. `null` hides consumers that require the capability. A successful selection replaces the snapshot with the host-confirmed committed and pending state; failures retain the previous state. Logged live `plan/mode` events commit `active` and clear `pending`, while reconnect re-queries the full state. A failed capability query never makes an otherwise usable conversation fail to open.
+Each opened `Session` queries the optional plan capability independently of paginated history and exposes `planMode: null | { active, pending? }` in its `ConversationSnapshot`. `null` hides consumers that require the capability; a present `pending` differs from `active`. A successful selection replaces the snapshot with the host-confirmed committed and pending state; failures retain the previous state. A shared request fence drops stale plan query and selection responses, while an event-version fence preserves a commit that overtakes a current unary request. Logged live `plan/mode` events commit `active` and clear `pending`; replacement history windows also fold their latest plan event so gap repair cannot miss a recovered commit. Reconnect re-queries the full state, and a failed capability query never makes an otherwise usable conversation fail to open.
 
 ## Model Experience
 

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

@@ -59,6 +59,10 @@ export class Session implements ObservableSnapshot<ConversationSnapshot> {
   private planCapabilityKnown = false
   /** Monotonic local fence for committed plan events observed on the mux stream. */
   private planEventVersion = 0
+  /** Highest plan event seq observed through an append or replacement window. */
+  private latestPlanEventSeq: number | null = null
+  /** Monotonic fence shared by plan queries and selections; only the latest response may land. */
+  private planRequestVersion = 0
   /** Latest valid commit, held until the initial capability query resolves. */
   private latestLivePlanMode: PlanModeState | null = null
   // Revision counters + caches backing the snapshot's reference-stability contract (§A.9.4/§C.2,
@@ -145,6 +149,7 @@ export class Session implements ObservableSnapshot<ConversationSnapshot> {
    */
   async setPlanMode(active: boolean): Promise<RpcResult<PlanModeState | null>> {
     const planEventVersion = this.planEventVersion
+    const planRequestVersion = ++this.planRequestVersion
     let result: RpcResult<PlanModeState | null>
     try {
       result = (await this.api.sessions.setPlanMode({ sessionId: this.sessionId, active })).result
@@ -152,8 +157,9 @@ export class Session implements ObservableSnapshot<ConversationSnapshot> {
       result = transportError(error)
     }
     if (result.ok) {
-      this.applyPlanResponse(result.value, planEventVersion)
-      this.notifier.notifyNow()
+      if (this.applyPlanResponse(result.value, planEventVersion, planRequestVersion)) {
+        this.notifier.notifyNow()
+      }
     }
     return result
   }
@@ -387,6 +393,7 @@ export class Session implements ObservableSnapshot<ConversationSnapshot> {
     this.hasMore = hasMore
     this.foldAdapter.reset(this.events, this.baseSeq, this.views)
     this.rebuildDerivedFromWindow()
+    this.applyLatestWindowPlanMode()
     const buffered = this.liveBuffer
     this.liveBuffer = []
     for (const item of buffered) this.appendLive(item.event, item.view)
@@ -411,10 +418,11 @@ export class Session implements ObservableSnapshot<ConversationSnapshot> {
    */
   private async refreshPlanMode(generation: number): Promise<void> {
     const planEventVersion = this.planEventVersion
+    const planRequestVersion = ++this.planRequestVersion
     try {
       const { result } = await this.api.sessions.planMode({ sessionId: this.sessionId })
       if (generation !== this.openGeneration) return
-      if (result.ok) this.applyPlanResponse(result.value, planEventVersion)
+      if (result.ok) this.applyPlanResponse(result.value, planEventVersion, planRequestVersion)
       else console.error('[web-runtime] plan-mode query failed:', result.error)
     } catch (error) {
       if (generation !== this.openGeneration) return
@@ -429,6 +437,8 @@ export class Session implements ObservableSnapshot<ConversationSnapshot> {
     if (typeof candidate.data !== 'object' || candidate.data === null) return
     const data = candidate.data as { active?: unknown }
     if (typeof data.active !== 'boolean') return
+    if (this.latestPlanEventSeq !== null && event.seq <= this.latestPlanEventSeq) return
+    this.latestPlanEventSeq = event.seq
     this.planEventVersion++
     this.latestLivePlanMode = { active: data.active }
     if (this.planCapabilityKnown && this.planMode !== null) {
@@ -436,20 +446,38 @@ export class Session implements ObservableSnapshot<ConversationSnapshot> {
     }
   }
 
+  /** Replacement windows bypass appendLive, so fold their newest valid plan commit explicitly. */
+  private applyLatestWindowPlanMode(): void {
+    for (let i = this.events.length - 1; i >= 0; i--) {
+      const before = this.latestPlanEventSeq
+      this.applyLivePlanMode(this.events[i] as SessionEvent)
+      if (this.latestPlanEventSeq !== before) return
+    }
+  }
+
   /**
-   * Apply a unary plan snapshot unless a newer mux commit crossed the request.
+   * Apply the latest unary plan snapshot unless a newer request or mux commit
+   * crossed it.
    * A successful null response establishes absence and never promotes a raw
    * event into a capability.
+   *
+   * @returns Whether this response was current and applied.
    */
-  private applyPlanResponse(value: PlanModeState | null, requestVersion: number): void {
+  private applyPlanResponse(
+    value: PlanModeState | null,
+    requestEventVersion: number,
+    requestVersion: number,
+  ): boolean {
+    if (requestVersion !== this.planRequestVersion) return false
     this.planCapabilityKnown = true
     if (value === null) {
       this.planMode = null
-      return
+      return true
     }
-    this.planMode = requestVersion === this.planEventVersion
+    this.planMode = requestEventVersion === this.planEventVersion
       ? value
       : this.latestLivePlanMode ?? value
+    return true
   }
 
   /** Land a live session/event (open/repair in flight -> buffer; overlapping seq -> drop;

packages/client/runtime/tests/session.spec.ts

@@ -96,6 +96,29 @@ describe('plan mode projection', () => {
     expect(result).toEqual({ ok: true, value: { active: false, pending: true } })
     expect(api.callsOf('session.setPlanMode')).toEqual([{ sessionId: SID, active: true }])
     expect(session.getSnapshot().planMode).toEqual({ active: false, pending: true })
+
+    api.onSetPlanMode = () => Promise.resolve(ok({ active: false }))
+    await session.setPlanMode(false)
+    expect(session.getSnapshot().planMode).toEqual({ active: false })
+  })
+
+  it('drops an older overlapping selection response after the newer selection lands', async () => {
+    const { api, session } = makeSession()
+    api.onPlanMode = () => Promise.resolve(ok({ active: false }))
+    await session.open()
+    const older = deferred<Awaited<ReturnType<FakeApiClient['onSetPlanMode']>>>()
+    const newer = deferred<Awaited<ReturnType<FakeApiClient['onSetPlanMode']>>>()
+    let call = 0
+    api.onSetPlanMode = () => ++call === 1 ? older.promise : newer.promise
+
+    const selectPlan = session.setPlanMode(true)
+    const selectDefault = session.setPlanMode(false)
+    newer.resolve(ok({ active: false }))
+    await selectDefault
+    older.resolve(ok({ active: false, pending: true }))
+    await selectPlan
+
+    expect(session.getSnapshot().planMode).toEqual({ active: false })
   })
 
   it('retains the prior state when a selection fails at the business or transport layer', async () => {
@@ -174,6 +197,26 @@ describe('plan mode projection', () => {
     expect(selection.session.getSnapshot().planMode).toEqual({ active: true })
   })
 
+  it('applies a plan commit recovered through a gap-repair replacement window', async () => {
+    const { api, session } = makeSession()
+    const initial = plainTurn(0, 0, 'a', 'b')
+    api.onHistory = () => histResponse(initial)
+    api.onPlanMode = () => Promise.resolve(ok({ active: false, pending: true }))
+    await session.open()
+
+    const planCommit = at(6, { type: 'plan/mode', data: { active: true } })
+    const later = ev.turnStart(7, 1)
+    api.onHistory = () => histResponse([...initial, planCommit, later])
+    session.handleMuxEnvelope('rp-gap' as never, {
+      type: 'session/event', sessionId: SID, event: later,
+    })
+
+    await vi.waitFor(() => {
+      expect(api.callsOf('session.history')).toHaveLength(2)
+      expect(session.getSnapshot().planMode).toEqual({ active: true })
+    })
+  })
+
   it('keeps history usable when the independent capability query fails', async () => {
     const business = makeSession()
     const errorSpy = vi.spyOn(console, 'error').mockImplementation(() => {})

packages/host/apiproxy/README.md

@@ -10,7 +10,7 @@ The layering/protocol decisions are recorded in the [GUI layering and RPC protoc
 
 The mux stream projects the latest log-backed title as a validated `session/title` control frame after each attached-session subscription baseline and immediately after the corresponding live raw title event. This projection does not add titles to `session.list`; cold sessions remain metadata-only there until opening or resuming attaches their logs.
 
-Plan mode uses two unary methods instead of deriving current state from a history page: `session.planMode` returns the committed state plus any boundary-pending selection, and `session.setPlanMode` records a selection and returns the same authoritative shape. Both return `null` when the optional host service is absent; `null` is capability absence, while `{ active: false }` is a supported inactive session. Committed changes still arrive through the raw logged `plan/mode` session event.
+Plan mode uses two unary methods instead of deriving current state from a history page: `session.planMode` returns the committed state plus any boundary-pending selection, and `session.setPlanMode` records a selection and returns the same authoritative shape. A present `pending` target must differ from `active`; a net-zero service cleanup intent projects as `{ active }`, and the wire schema rejects equal values. Both methods return `null` when the optional host service is absent; `null` is capability absence, while `{ active: false }` is a supported inactive session. Committed changes still arrive through the raw logged `plan/mode` session event.
 
 ## Carrier layer (`/client` + root)
 

packages/host/apiproxy/src/api/sessions.schema.ts

@@ -113,7 +113,10 @@ export const sessionCancelValueSchema = z.object({
 export const planModeStateSchema = z.object({
   active: z.boolean(),
   pending: z.boolean().optional(),
-}) satisfies z.ZodType<Wire<PlanModeState>>
+}).refine(
+  state => state.pending === undefined || state.pending !== state.active,
+  { message: 'pending must differ from active when present', path: ['pending'] },
+) satisfies z.ZodType<Wire<PlanModeState>>
 
 /** session.planMode request payload. */
 export const sessionPlanModeRequestSchema = z.object({

packages/host/apiproxy/src/api/sessions.ts

@@ -47,7 +47,7 @@ export interface SessionSummary {
 /**
  * Plan collaboration state exposed to clients. `active` is the logged state
  * shaping the current request; `pending`, when present, is the user's
- * next-boundary selection.
+ * next-boundary selection and differs from `active`.
  */
 export interface PlanModeState {
   active: boolean

packages/host/apiproxy/tests/rpc-schemas.spec.ts

@@ -114,6 +114,8 @@ describe('sessions domain schemas', () => {
     expect(sessionSetPlanModeValueSchema.parse({ active: true })).toEqual({ active: true })
     expect(() => sessionSetPlanModeRequestSchema.parse({ sessionId: 's1', active: 'yes' })).toThrow()
     expect(() => sessionPlanModeValueSchema.parse({ active: 'yes' })).toThrow()
+    expect(() => sessionPlanModeValueSchema.parse({ active: false, pending: false })).toThrow()
+    expect(() => sessionSetPlanModeValueSchema.parse({ active: true, pending: true })).toThrow()
     expect(contentBlockSchema.parse({ type: 'text', text: 'x', extra: 1 })).toMatchObject({ extra: 1 })
   })
 })

packages/host/runtime/README.md

@@ -18,7 +18,7 @@ Which plugins mount and with what defaults is decided only here — shells must
 
 ## ApiProxy implementation notes
 
-Unary methods take the narrow `RpcRequest<P>` and echo `request.rpcId`; a prompt's rpcId rides `MessageSource` into the `user/message` event so clients can promote optimistic echoes. `history`/`prompt` on a cold session implicitly resume it, deduplicating concurrent calls through an in-flight table; `history` paginates backwards on message boundaries (never mid-message). `planMode` and `setPlanMode` use the same resume path, project the optional `ctx.planMode` service, and return `null` when it is not mounted. The mux stream replays a `session/subscribed` baseline per attached session and every still-pending question with its original rpcId. Question responses, including blank per-item answers, are validated against the owning session and exact request before an atomic first-wins claim; answer, whole-request cancellation, owner abort, and provider disposal broadcast `question/resolved`. The host stream carries session lifecycle, running flips, and `agent/error` as the only outlet for live failures with no turn position.
+Unary methods take the narrow `RpcRequest<P>` and echo `request.rpcId`; a prompt's rpcId rides `MessageSource` into the `user/message` event so clients can promote optimistic echoes. `history`/`prompt` on a cold session implicitly resume it, deduplicating concurrent calls through an in-flight table; `history` paginates backwards on message boundaries (never mid-message). `planMode` and `setPlanMode` use the same resume path, project the optional `ctx.planMode` service, canonicalize a net-zero cleanup intent by omitting `pending`, and return `null` when the service is not mounted. The mux stream replays a `session/subscribed` baseline per attached session and every still-pending question with its original rpcId. Question responses, including blank per-item answers, are validated against the owning session and exact request before an atomic first-wins claim; answer, whole-request cancellation, owner abort, and provider disposal broadcast `question/resolved`. The host stream carries session lifecycle, running flips, and `agent/error` as the only outlet for live failures with no turn position.
 
 ## Model Experience
 

packages/host/runtime/src/api-proxy.ts

@@ -12,7 +12,8 @@ import type { JsonValue, Session, SessionEvent, SessionHeader, SessionId } from
 import type { SessionPersistence } from '@deepseek-ai/dsh-session-persistence'
 import { foldSessionTitle } from '@deepseek-ai/dsh-session-title'
 import type {
-  ApiProxy, HistoryEntry, HostFrame, MuxFrame, QuestionResponsePayload, SessionSummary, ToolEventView,
+  ApiProxy, HistoryEntry, HostFrame, MuxFrame, PlanModeState, QuestionResponsePayload, SessionSummary,
+  ToolEventView,
 } from '@deepseek-ai/dsh-host-apiproxy/api'
 import { questionResponsePayloadSchema } from '@deepseek-ai/dsh-host-apiproxy/api/questions.schema'
 import type { ClientResponse, RpcError, RpcReceipt, RpcRequest, RpcResponse } from '@deepseek-ai/dsh-host-apiproxy/api/rpc'
@@ -65,6 +66,16 @@ function ok<T>(request: RpcRequest<unknown>, value: T): RpcResponse<T> {
   return { rpcId: request.rpcId, result: { ok: true, value } }
 }
 
+/**
+ * Project the service's boundary-cleanup intent into canonical wire state.
+ * A target equal to the committed value has no user-visible pending effect.
+ */
+function projectPlanModeState(state: PlanModeState): PlanModeState {
+  return state.pending !== undefined && state.pending === state.active
+    ? { active: state.active }
+    : state
+}
+
 /** Wrap an error result echoing the request's rpcId. */
 function err<T>(request: RpcRequest<unknown>, error: RpcError): RpcResponse<T> {
   return { rpcId: request.rpcId, result: { ok: false, error } }
@@ -466,7 +477,7 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
         const found = await agentFor(request.payload.sessionId)
         if ('error' in found) return err(request, found.error)
         const planMode = ctx.get('planMode')
-        return ok(request, planMode?.get(found.agent) ?? null)
+        return ok(request, planMode === undefined ? null : projectPlanModeState(planMode.get(found.agent)))
       },
 
       async setPlanMode(request) {
@@ -475,7 +486,7 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
         const planMode = ctx.get('planMode')
         if (planMode === undefined) return ok(request, null)
         planMode.set(found.agent, request.payload.active)
-        return ok(request, planMode.get(found.agent))
+        return ok(request, projectPlanModeState(planMode.get(found.agent)))
       },
     },
 

packages/host/runtime/tests/host-runtime.spec.ts

@@ -256,8 +256,8 @@ describe('sessions.planMode / setPlanMode', () => {
     })
     expect(expectOk(await running.api.sessions.setPlanMode(request({ sessionId, active: false })))).toEqual({
       active: false,
-      pending: false,
     })
+    expect(expectOk(await running.api.sessions.planMode(request({ sessionId })))).toEqual({ active: false })
   })
 
   it('returns the normal session-not-found error for both methods', async () => {