fix(gui): tail history page carries the full-log todo projection

The client's todos projection derived only from the paged display window,
so reopening a session whose last todo/write preceded the tail page showed
an empty plan until the user paged back — session-level state cannot be
reconstructed from an arbitrary window. The host owns the full log, so the
tail history response now attaches todos (latest todo/write backscan, the
same posture as the view pairing); installWindow seeds it, window rebuilds
preserve it, and any in-window or live write keeps overwriting it. The
fixture mirrors the host; docs and both Agent Notes record the mechanism.

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

@@ -5,7 +5,7 @@
  */
 
 import type { ContentBlock } from '@deepseek-ai/dsh-llm/types'
-import type { SessionEvent, SessionId } from '@deepseek-ai/dsh-session/types'
+import type { SessionEvent, SessionId, TodoItem } from '@deepseek-ai/dsh-session/types'
 import type { RpcId, RpcRequest, RpcResponse } from './rpc.ts'
 import type { ToolEventView } from './events.ts'
 
@@ -60,9 +60,13 @@ export interface SessionsApi {
    * Each entry pairs the raw SessionEvent with the host-computed view (tool events whose
    * presenter produced one, evaluated against the registry at pagination time); the client
    * rebuilds the surface from the events with the shared fold.
+   * The tail page (beforeSeq absent) also carries `todos` — the session's current todo
+   * projection (latest `todo/write` over the FULL log, independent of the page window) —
+   * so a paged client restores the plan without walking history; absent when the session
+   * never wrote one. Older pages omit it (the projection is session-level, not per-page).
    */
   history(request: RpcRequest<{ sessionId: SessionId; beforeSeq?: number; maxMessages?: number }>):
-  Promise<RpcResponse<{ events: HistoryEntry[]; hasMore: boolean }>>
+  Promise<RpcResponse<{ events: HistoryEntry[]; hasMore: boolean; todos?: TodoItem[] }>>
 
   /** Sends a message. content is core's ContentBlock[] verbatim; mode maps 1:1 — queue→send, steer→steer. */
   prompt(request: RpcRequest<{ sessionId: SessionId; mode: 'queue' | 'steer'; content: ContentBlock[] }>):

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

@@ -8,7 +8,7 @@ import { mkdir, stat } from 'node:fs/promises'
 import type { Context } from 'cordis'
 import type { Agent, AgentStatus } from '@deepseek-ai/dsh-agent'
 import type { ContentBlock, MessageSource } from '@deepseek-ai/dsh-llm'
-import type { JsonValue, Session, SessionEvent, SessionHeader, SessionId } from '@deepseek-ai/dsh-session'
+import type { JsonValue, Session, SessionEvent, SessionHeader, SessionId, TodoItem } from '@deepseek-ai/dsh-session'
 import type { SessionPersistence } from '@deepseek-ai/dsh-session-persistence'
 import { foldSessionTitle } from '@deepseek-ai/dsh-session-title'
 import type {
@@ -265,6 +265,15 @@ function backscanArgs(events: readonly SessionEvent[], callId: string): { name:
   return undefined
 }
 
+/** Current todo projection: the latest `todo/write` over the full log (whole-list replace ⇒ last write wins); undefined when none. */
+function backscanTodos(events: readonly SessionEvent[]): TodoItem[] | undefined {
+  for (let i = events.length - 1; i >= 0; i--) {
+    const event = events[i]
+    if (event !== undefined && event.type === 'todo/write') return event.data.todos
+  }
+  return undefined
+}
+
 /**
  * Thrown by the cold-resume path when the id names no servable session
  * (absent from the store, or a pre-project legacy log without a cwd).
@@ -435,7 +444,11 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
           const view = viewFor(ctx, event, callId => backscanArgs(page.events, callId))
           return { event, ...view === undefined ? {} : { view } }
         })
-        return ok(request, { events: entries, hasMore: page.hasMore })
+        // Tail page carries the session-level todo projection over the FULL
+        // log (the page window may not contain the last todo/write; a paged
+        // client cannot reconstruct session-level state from it).
+        const todos = beforeSeq === undefined ? backscanTodos(found.agent.session.events) : undefined
+        return ok(request, { events: entries, hasMore: page.hasMore, ...todos === undefined ? {} : { todos } })
       },
 
       async prompt(request) {

packages/host/runtime/tests/api-proxy-view.spec.ts

@@ -154,6 +154,39 @@ describe('mux live view computation', () => {
     expect('view' in (byKey.get('tool/result:h-plain') ?? {})).toBe(false)
   })
 
+  it('tail page carries the full-log todo projection; older pages and todo-less sessions omit it', async () => {
+    const { ctx } = await harness()
+    const api = createApiProxy(ctx, { provider: 'p', model: 'm', cwd: '/tmp' })
+    const session = ctx.sessions.create()
+    ctx.agents.register({ id: session.id, session, status: 'idle', ctx } as Agent)
+    // Superseded write early in the log, latest write later; enough messages to page.
+    session.append('todo/write', { todos: [{ content: 'old', status: 'pending' }] })
+    for (let turn = 0; turn < 6; turn++) {
+      session.append('turn/start', { turn, trigger: { kind: 'message', source: { kind: 'user' } } })
+      session.append('user/message', { content: [{ type: 'text', text: `q${turn}` }], source: { kind: 'user' } }, { surfaceOp: 'append' })
+      session.append('assistant/message', { turn, step: 0, content: [{ type: 'text', text: `a${turn}` }], provenance: { provider: 'p', model: 'm' } }, { surfaceOp: 'append' })
+      session.append('turn/end', { turn, reason: { kind: 'completed' } })
+    }
+    session.append('todo/write', { todos: [{ content: 'current', status: 'in_progress' }] })
+
+    // Tail page limited to 2 messages: the latest todo/write may or may not sit
+    // in the window — the projection must come from the FULL log either way.
+    const tail = await api.sessions.history({ rpcId: RpcId('t-todos'), payload: { sessionId: session.id, maxMessages: 2 } })
+    if (!tail.result.ok) throw new Error('history failed')
+    expect(tail.result.value.todos).toEqual([{ content: 'current', status: 'in_progress' }])
+    // An older page omits the projection (session-level, tail-page-only).
+    const boundary = tail.result.value.events[0]?.event.seq ?? 0
+    const older = await api.sessions.history({ rpcId: RpcId('t-todos-2'), payload: { sessionId: session.id, beforeSeq: boundary, maxMessages: 2 } })
+    if (!older.result.ok) throw new Error('older failed')
+    expect('todos' in older.result.value).toBe(false)
+    // A session with no todo/write anywhere omits the field.
+    const bare = ctx.sessions.create()
+    ctx.agents.register({ id: bare.id, session: bare, status: 'idle', ctx } as Agent)
+    const bareTail = await api.sessions.history({ rpcId: RpcId('t-todos-3'), payload: { sessionId: bare.id } })
+    if (!bareTail.result.ok) throw new Error('bare failed')
+    expect('todos' in bareTail.result.value).toBe(false)
+  })
+
   it('drops a disposed session from the live open-call table (result after dispose gets no view)', async () => {
     const { ctx } = await harness()
     const api = createApiProxy(ctx, { provider: 'p', model: 'm', cwd: '/tmp' })