refactor: tool-todo registers the todos unit (init/apply/view); backscan removed

packages/todo/tool-todo/README.md

@@ -24,7 +24,7 @@ The canonical result is `{ todos, counts: { pending, inProgress, completed } }`;
 
 ## Session projection
 
-When the composition mounts `ctx.sessionProjections` ([`@deepseek-ai/dsh-session-projection`](../../session-projection/session-projection/README.md)), this package registers the `todos` provider under an injected child: value = the latest `todo/write` snapshot backscanned from the in-memory log tail (whole list, last-wins), `null` before the first write. The key merges into `SessionProjectionMap` here (via the interface package's `/types` outlet); carriers serve it on the history tail page. Compositions without the registry are unaffected.
+When the composition mounts `ctx.sessionProjections` ([`@deepseek-ai/dsh-session-projection`](../../session-projection/session-projection/README.md)), this package registers the `todos` projection unit under an injected child: `init` = `null` (no write yet), `apply` = take the whole list from each `todo/write` (last-wins; every other event returns the same state reference), `view` = identity, `stateVersion` = 1. The key merges into `SessionProjectionMap` here (via the interface package's `/types` outlet); the framework drives the unit and carriers serve the value on the history tail page and the `session/projection` push frame. Compositions without the registry are unaffected.
 
 ## Export shape
 

packages/todo/tool-todo/src/index.ts

@@ -9,9 +9,8 @@ import type { Context } from 'cordis'
 import { z } from 'zod'
 import type { ZodType } from 'zod'
 import { defineTool } from '@deepseek-ai/dsh-tools'
-import type { Agent } from '@deepseek-ai/dsh-agent'
-import type { SessionEvent, TodoItem } from '@deepseek-ai/dsh-session'
-// Type-only: resolves ctx.sessionProjections for the optional provider child.
+import type { TodoItem } from '@deepseek-ai/dsh-session'
+// Type-only: resolves ctx.sessionProjections for the optional unit child.
 import type {} from '@deepseek-ai/dsh-session-projection'
 
 declare module '@deepseek-ai/dsh-session-projection/types' {
@@ -82,29 +81,20 @@ const todosProjectionSchema: ZodType<TodoItem[] | null> = z.union([
   z.null(),
 ])
 
-/**
- * Current whole todo list: the latest `todo/write` snapshot, backscanned from
- * the log tail (bounded: first hit terminates; the events live in memory).
- * `null` = no write yet.
- */
-function currentTodos(agent: Agent): TodoItem[] | null {
-  const events = agent.session.events
-  for (let i = events.length - 1; i >= 0; i--) {
-    const event = events[i] as SessionEvent
-    if (event.type === 'todo/write') return event.data.todos
-  }
-  return null
-}
-
-/** Register the `todo_write` tool on `ctx.tools` and, when the session-projection seam is composed, the `todos` provider. */
+/** Register the `todo_write` tool on `ctx.tools` and, when the session-projection seam is composed, the `todos` unit. */
 export function apply(ctx: Context): void {
-  // The provider child activates only when a projection registry is composed
-  // (headless assemblies without the seam stay unaffected).
+  // The unit child activates only when a projection registry is composed
+  // (headless assemblies without the seam stay unaffected). Pure last-wins
+  // fold: state is the latest whole todo/write list, null before the first
+  // write; every other event returns the same reference (no downstream work).
   ctx.inject(['sessionProjections'], (projectionCtx) => {
-    projectionCtx.sessionProjections.register({
+    projectionCtx.sessionProjections.register<'todos', TodoItem[] | null>({
       key: 'todos',
       schema: todosProjectionSchema,
-      get: currentTodos,
+      init: () => null,
+      apply: (state, event) => (event.type === 'todo/write' ? event.data.todos : state),
+      view: state => state,
+      stateVersion: 1,
     })
   })
   ctx.tools.register(defineTool({

packages/todo/tool-todo/tests/projection.spec.ts

@@ -2,7 +2,7 @@
  * The `todos` projection provider (session-projection RFC knife 4 — the "a
  * fourth domain is just its own registrations" acceptance probe): mounting
  * tool-todo beside the registry serves the whole current list on the history
- * tail page with a consistent asOfSeq; before any write the value is null; a
+ * tail page with a consistent asOfSeq (= last event seq); before any write the value is null; a
  * composition without tool-todo has no `todos` key; unmounting tool-todo
  * removes it (HMR safety). The carrier and framework are exercised unmodified.
  */
@@ -67,10 +67,10 @@ describe('todos projection provider', () => {
     seedMessage(bench.session)
     const projections = await bench.tailProjections()
     expect(projections?.values).toEqual({ todos: null })
-    expect(projections?.asOfSeq).toBe(bench.session.seq)
+    expect(projections?.asOfSeq).toBe(bench.session.seq - 1)
   })
 
-  it('serves the latest whole list after writes, asOfSeq = window tail seq', async () => {
+  it('serves the latest whole list after writes, asOfSeq = last event seq', async () => {
     const bench = await harness(true)
     const session = bench.session
     seedMessage(session)
@@ -84,7 +84,7 @@ describe('todos projection provider', () => {
     const projections = await bench.tailProjections()
     // Last-wins: the latest snapshot, whole.
     expect(projections?.values.todos).toEqual(second)
-    expect(projections?.asOfSeq).toBe(session.seq)
+    expect(projections?.asOfSeq).toBe(session.seq - 1)
   })
 
   it('has no todos key when tool-todo is not composed', async () => {