Merge remote-tracking branch 'origin/master' into xtr/identified-immutable-messages

# Conflicts:
#	docs/event-producer-consumer.md
#	packages/client/connection/src/client/fixture.ts
#	packages/goal/command-goal/tests/command-goal.spec.ts
#	packages/host/apiproxy/src/api-proxy.ts
#	packages/host/apiproxy/src/api/events.schema.ts
#	packages/host/apiproxy/src/api/events.ts
#	packages/host/apiproxy/tests/api-proxy-view.spec.ts
#	packages/host/apiproxy/tests/rpc-schemas.spec.ts
#	tsconfig.base.json

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

@@ -14,9 +14,8 @@ import type {
 import { createUserMessage, ReasoningEffortId } from '@deepseek-ai/dsh-llm'
 import { errorChain } from '@deepseek-ai/dsh-llm'
 import type { MessageId, MessageSource } from '@deepseek-ai/dsh-llm'
-import type { Session, SessionEvent, SessionHeader, SessionId, TodoItem, UserMessage } from '@deepseek-ai/dsh-session'
+import type { Session, SessionEvent, SessionHeader, SessionId, UserMessage } from '@deepseek-ai/dsh-session'
 import type { SessionPersistence } from '@deepseek-ai/dsh-session-persistence'
-import { foldSessionTitle } from '@deepseek-ai/dsh-session-title'
 import type { Workspace, WorkspaceRecord } from '@deepseek-ai/dsh-workspace'
 import {
   workspaceDomainState, workspaceRecord, WorkspaceId as brandWorkspaceId,
@@ -26,9 +25,11 @@ import {
 import type {} from '@deepseek-ai/dsh-tools'
 import type {
   ApiProxy, HistoryEntry, HostFrame, ModelCatalogFailure, ModelProviderGroup, ModelReasoning,
-  MuxFrame, QuestionResponsePayload, SessionSummary, ToolEventView,
+  MuxFrame, QuestionResponsePayload, SessionProjectionsBlock, SessionSummary, ToolEventView,
   WorkspaceId, WorkspaceView,
 } from './api/index.ts'
+// Type-only: resolves `ctx.get('sessionProjections')` to the projection registry.
+import type {} from '@deepseek-ai/dsh-session-projection'
 // Type-only edges: resolve `ctx.get('commands')`, the `commands/change` event, and `ctx.get('skills')`.
 import type {} from '@deepseek-ai/dsh-commands'
 import type {} from '@deepseek-ai/dsh-skill'
@@ -40,6 +41,7 @@ import type {
 } from '@deepseek-ai/dsh-user-interaction'
 import { UserInteractionError } from '@deepseek-ai/dsh-user-interaction'
 import { pickNativeDirectory } from './native-directory-picker.ts'
+import { openNativePath } from './native-path-opener.ts'
 
 /** Page size when history is called without maxMessages. */
 const DEFAULT_MAX_MESSAGES = 50
@@ -129,26 +131,9 @@ function frame<F>(payload: F): RpcRequest<F> {
   return { rpcId: RpcId(randomUUID()), payload }
 }
 
-type SessionTitleFrame = Extract<MuxFrame, { type: 'session/title' }>
-
-/** Project the latest durable title without exposing title-generation policy. */
-function titleFrame(session: Session): SessionTitleFrame | undefined {
-  const title = foldSessionTitle(session.events)
-  if (title === undefined) return undefined
-  return {
-    type: 'session/title',
-    sessionId: session.id,
-    title: title.title,
-    eventSeq: title.eventSeq,
-    updatedAt: title.updatedAt,
-  }
-}
-
-/** Queue the subscription baseline followed by its optional title snapshot. */
+/** Queue the subscription baseline frame. */
 function subscribeSession(queue: FrameQueue<RpcRequest<MuxFrame>>, session: Session): void {
   queue.push(frame({ type: 'session/subscribed', sessionId: session.id, lastSeq: session.seq - 1 }))
-  const title = titleFrame(session)
-  if (title !== undefined) queue.push(frame(title))
 }
 
 /** SessionSummary projection for attached (in-memory) sessions. */
@@ -203,6 +188,8 @@ export interface ApiProxyDefaults {
   workspaceRoot: string
   /** Native single-directory picker; injectable for carrier tests. */
   pickDirectory?: (signal: AbortSignal) => Promise<string | null>
+  /** Native open-with-default-application; injectable for carrier tests. */
+  openPath?: (path: string, signal: AbortSignal) => Promise<void>
 }
 
 /** The tool/call payload fields the presenter path reads. */
@@ -295,13 +282,19 @@ 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
+/**
+ * The projection baseline for one history tail page: the registry's
+ * watermark-cache snapshot — one fully synchronous read (no await between the
+ * page slice and this), so all values and `asOfSeq` form a single consistent
+ * cut and `asOfSeq` equals the window tail event seq. The carrier holds zero
+ * domain knowledge (each value passed its unit's own schema inside the
+ * registry). An absent registry means the deployment has no projection seam:
+ * the whole block is absent and clients treat every key as capability-absent.
+ */
+function projectionsFor(ctx: Context, agent: Agent): SessionProjectionsBlock | undefined {
+  const registry = ctx.get('sessionProjections')
+  if (registry === undefined) return undefined
+  return registry.snapshot(agent.session)
 }
 
 /**
@@ -420,6 +413,16 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
     for (const queue of muxQueues) queue.push(envelope)
   }
 
+  // Projection change feed → session/projection push frames. The carrier
+  // mints the wire frame (the seam package holds no wire vocabulary); the
+  // child activates only when a projection registry is composed, and the
+  // subscription unwinds with this gateway's fiber.
+  ctx.inject(['sessionProjections'], (projectionCtx) => {
+    projectionCtx.sessionProjections.onChanged((session, key, value, seq) => {
+      broadcast({ type: 'session/projection', sessionId: session.id, key, value, seq })
+    })
+  })
+
   /**
    * Per-session inbox occurrence mirror serving the mux-open queue snapshot
    * (the same refresh-recovery baseline as pending questions). Each terminal
@@ -715,6 +718,8 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
         const { sessionId, beforeSeq, maxMessages } = request.payload
         const found = await agentFor(sessionId)
         if ('error' in found) return err(request, found.error)
+        // Everything below the resume above is synchronous: the page slice,
+        // the seq read, and the projection walk see one un-torn session state.
         const page = paginate(found.agent.session.events, beforeSeq, maxMessages ?? DEFAULT_MAX_MESSAGES)
         // Views are computed against the registry at pagination time; result
         // pairing scans within the page only (message-boundary pagination keeps
@@ -723,11 +728,14 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
           const view = viewFor(ctx, event, callId => backscanArgs(page.events, callId))
           return { event, ...view === undefined ? {} : { view } }
         })
-        // 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 } })
+        // Baseline rider: tail page only — loadOlder (beforeSeq present) is
+        // the one path that never needs a fresh projection baseline.
+        const projections = beforeSeq === undefined ? projectionsFor(ctx, found.agent) : undefined
+        return ok(request, {
+          events: entries,
+          hasMore: page.hasMore,
+          ...projections === undefined ? {} : { projections },
+        })
       },
 
       async models(request) {
@@ -1017,6 +1025,28 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
           })
         }
       },
+
+      async openPath(request, signal) {
+        try {
+          const open = defaults.openPath
+            ?? ((path: string, openSignal: AbortSignal) => openNativePath(path, openSignal))
+          await open(request.payload.path, signal)
+          return ok(request, { opened: true as const })
+        } catch (error: unknown) {
+          if (signal.aborted) {
+            return err(request, {
+              code: 'cancelled',
+              message: 'path open was aborted',
+              details: {},
+            })
+          }
+          return err(request, {
+            code: 'internal',
+            message: `path open failed: ${error instanceof Error ? error.message : String(error)}`,
+            details: {},
+          })
+        }
+      },
     },
 
     commands: {
@@ -1044,12 +1074,15 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
         const found = await agentFor(sessionId)
         if ('error' in found) return err(request, found.error)
         try {
-          const result = await commands.execute(found.agent, line, signal)
-          if (result === undefined) return ok(request, { matched: false })
-          return ok(request, {
-            matched: true,
-            result: { kind: result.kind, ...result.text === undefined ? {} : { text: result.text } },
-          })
+          // Pure admission: the executor's durable command/run + command/done
+          // pair (broadcast on the mux stream) carries the outcome; the
+          // response reports whether the line resolved to a handler, plus the
+          // minted pairing id so the issuing client can correlate its request
+          // with the flow node the lifecycle events produce.
+          const execution = await commands.execute(found.agent, line, signal)
+          return ok(request, execution === undefined
+            ? { matched: false }
+            : { matched: true, commandId: execution.commandId })
         } catch (error: unknown) {
           if (signal.aborted) return err(request, { code: 'cancelled', message: 'command execution was aborted', details: {} })
           return err(request, { code: 'internal', message: `command failed: ${String(error)}`, details: {} })
@@ -1151,10 +1184,6 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
             const view = viewFor(ctx, event, callId =>
               openCalls.get(session.id)?.get(callId) ?? backscanArgs(session.events, callId))
             queue.push(frame({ type: 'session/event', sessionId: session.id, event, ...view === undefined ? {} : { view } }))
-            if (event.type === 'session/title') {
-              // The accepted raw event is already in session.events, so the fold must find it.
-              queue.push(frame(titleFrame(session) as SessionTitleFrame))
-            }
           }),
           ctx.on('session/created', (session: Session) => {
             subscribeSession(queue, session)

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

@@ -4,10 +4,11 @@
  */
 
 import { z } from 'zod'
+import type { CommandId } from '@deepseek-ai/dsh-commands/brand'
 import type { RequestPayload, ResponseValue } from './rpc-map.ts'
 import type { Wire } from './rpc.schema.ts'
 import { sessionIdSchema } from './sessions.schema.ts'
-import type { CommandDescriptor, CommandExecuteResult } from './commands.ts'
+import type { CommandDescriptor } from './commands.ts'
 
 /** CommandDescriptor row of command.list. */
 export const commandDescriptorSchema = z.object({
@@ -32,14 +33,12 @@ export const commandExecuteRequestSchema = z.object({
   line: z.string(),
 }) satisfies z.ZodType<Wire<RequestPayload<'command.execute'>>>
 
-/** Detached command outcome (result slot of command.execute's value). */
-export const commandExecuteResultSchema = z.object({
-  kind: z.union([z.literal('success'), z.literal('error')]),
-  text: z.string().optional(),
-}) satisfies z.ZodType<Wire<CommandExecuteResult>>
+/** CommandId: one brand cast after shape validation (the only cast point in this domain). */
+export const commandIdSchema = z.string().min(1) as unknown as z.ZodType<CommandId>
 
-/** command.execute response value (matched=false carries no result). */
+/** command.execute response value: pure admission — outcomes ride the logged
+ * lifecycle events; commandId (present exactly when matched) correlates with them. */
 export const commandExecuteValueSchema = z.object({
   matched: z.boolean(),
-  result: commandExecuteResultSchema.optional(),
+  commandId: commandIdSchema.optional(),
 }) satisfies z.ZodType<Wire<ResponseValue<'command.execute'>>>

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

@@ -5,6 +5,7 @@
  * together), so there is no agent-less surface on this wire.
  */
 
+import type { CommandId } from '@deepseek-ai/dsh-commands/brand'
 import type { SessionId } from '@deepseek-ai/dsh-session/types'
 import type { RpcRequest, RpcResponse } from './rpc.ts'
 
@@ -22,12 +23,6 @@ export interface CommandDescriptor {
   readonly input?: { readonly hint: string }
 }
 
-/** Detached command outcome rendered directly by the requesting client. */
-export interface CommandExecuteResult {
-  readonly kind: 'success' | 'error'
-  readonly text?: string
-}
-
 /** Command-domain unary methods (the map keys command.* of RpcMethodMap). */
 export interface CommandsApi {
   /**
@@ -38,11 +33,16 @@ export interface CommandsApi {
 
   /**
    * Parses and executes one slash-command line against the addressed agent
-   * without sending it to the model. matched=false when syntax or name does
-   * not resolve (the client falls back to its default sink). The signal rides
-   * beside the request, never on the wire: the fetch carrier's request signal
-   * cancels the running handler.
+   * without sending it to the model — pure admission semantics. matched=false
+   * when syntax or name does not resolve (the client falls back to its
+   * default sink). The handler's outcome does NOT ride the response: the host
+   * executor durably logs the lifecycle (`command/run`/`command/done`), which
+   * broadcasts on the mux stream and renders as a persistent flow node.
+   * `commandId` is present exactly when matched — the minted lifecycle
+   * pairing id, letting the issuing client correlate this acknowledgment
+   * with that flow node. The signal rides beside the request, never on the
+   * wire: the fetch carrier's request signal cancels the running handler.
    */
   execute(request: RpcRequest<{ sessionId: SessionId; line: string }>, signal: AbortSignal):
-  Promise<RpcResponse<{ matched: boolean; result?: CommandExecuteResult }>>
+  Promise<RpcResponse<{ matched: boolean; commandId?: CommandId }>>
 }

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

@@ -35,7 +35,6 @@ const messageSchema = z.object({
 export const muxFrameSchema = z.discriminatedUnion('type', [
   z.object({ type: z.literal('session/event'), sessionId: sessionIdSchema, event: sessionEventSchema, view: toolEventViewSchema.optional() }),
   z.object({ type: z.literal('session/subscribed'), sessionId: sessionIdSchema, lastSeq: z.number().int() }),
-  z.object({ type: z.literal('session/title'), sessionId: sessionIdSchema, title: z.string().min(1), eventSeq: z.number().int().nonnegative(), updatedAt: z.number() }),
   z.object({ type: z.literal('approval/requested'), sessionId: sessionIdSchema, approvalId: approvalRequestIdSchema, toolName: z.string(), callId: z.string().optional(), reason: z.string().optional() }),
   z.object({ type: z.literal('approval/resolved'), sessionId: sessionIdSchema, approvalId: approvalRequestIdSchema, outcome: z.union([z.literal('allowed-once'), z.literal('rejected'), z.literal('cancelled'), z.literal('unavailable')]) }),
   // Non-empty by wire contract: the user-interaction service rejects empty
@@ -44,6 +43,9 @@ export const muxFrameSchema = z.discriminatedUnion('type', [
   z.object({ type: z.literal('question/requested'), sessionId: sessionIdSchema, questions: z.array(askUserQuestionItemSchema).min(1) }),
   z.object({ type: z.literal('question/resolved'), sessionId: sessionIdSchema, questionRpcId: rpcIdSchema, outcome: z.union([z.literal('answered'), z.literal('cancelled')]) }),
   z.object({ type: z.literal('session/queued'), sessionId: sessionIdSchema, message: messageSchema, steering: z.boolean() }),
+  // value stays wide: it already passed its unit's own schema on the host,
+  // and deep-validating here would import every domain's schema into the carrier.
+  z.object({ type: z.literal('session/projection'), sessionId: sessionIdSchema, key: z.string().min(1), value: z.unknown(), seq: z.number().int().nonnegative() }),
   z.object({ type: z.literal('stream/error'), error: rpcErrorSchema }),
 ]) as unknown as z.ZodType<MuxFrame>
 

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

@@ -35,9 +35,9 @@ export type ToolEventView =
 export interface EventsApi {
   /**
    * All-session aggregated mux stream. On open, emits a subscribed control frame for every
-   * attached session followed by its optional latest title snapshot, then replays each
-   * session's still-pending approval/question requested frames (rpcId reused verbatim — the
-   * refresh-recovery baseline).
+   * attached session, then replays each session's still-pending approval/question requested
+   * frames (rpcId reused verbatim — the refresh-recovery baseline). Session titles ride the
+   * generic projection pair (history-tail projections block + session/projection frames).
    * since: resume seam, unimplemented in v1 (ignored if passed); reconnection = reopen the
    * stream + refetch history.
    */
@@ -57,7 +57,6 @@ export interface EventsApi {
 export type MuxFrame =
   | { type: 'session/event'; sessionId: SessionId; event: SessionEvent; view?: ToolEventView }
   | { type: 'session/subscribed'; sessionId: SessionId; lastSeq: number }
-  | { type: 'session/title'; sessionId: SessionId; title: string; eventSeq: number; updatedAt: number }
   | { type: 'approval/requested'; sessionId: SessionId; approvalId: ApprovalRequestId; toolName: string; callId?: CallId; reason?: string }
   | { type: 'approval/resolved'; sessionId: SessionId; approvalId: ApprovalRequestId; outcome: ApprovalOutcome }
   | { type: 'question/requested'; sessionId: SessionId; questions: AskUserQuestionItem[] }
@@ -75,6 +74,15 @@ export type MuxFrame =
    * reconciliation key).
    */
   | { type: 'session/queued'; sessionId: SessionId; message: Message; steering: boolean }
+  /**
+   * One projection unit's finished value changed (session-projection RFC).
+   * Live push state, never logged — replay recomputes on the host (the
+   * tool-view posture). `value` is the unit's schema-validated view output;
+   * `seq` is the unit's watermark at emission. Clients keep one generic
+   * per-session value store under higher-seq-wins, seeded by the history
+   * tail page's projections block.
+   */
+  | { type: 'session/projection'; sessionId: SessionId; key: string; value: unknown; seq: number }
   | { type: 'stream/error'; error: RpcError }
 
 /**

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

@@ -25,3 +25,13 @@ export const hostPickDirectoryRequestSchema = z.object({}) satisfies z.ZodType<W
 export const hostPickDirectoryValueSchema = z.object({
   path: z.string().nullable(),
 }) satisfies z.ZodType<Wire<ResponseValue<'host.pickDirectory'>>>
+
+/** host.openPath request payload. */
+export const hostOpenPathRequestSchema = z.object({
+  path: z.string().min(1),
+}) satisfies z.ZodType<Wire<RequestPayload<'host.openPath'>>>
+
+/** host.openPath response value. */
+export const hostOpenPathValueSchema = z.object({
+  opened: z.literal(true),
+}) satisfies z.ZodType<Wire<ResponseValue<'host.openPath'>>>

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

@@ -28,4 +28,14 @@ export interface HostApi {
     request: RpcRequest<{}>,
     signal: AbortSignal,
   ): Promise<RpcResponse<{ path: string | null }>>
+
+  /**
+   * Open a filesystem path with the operating system's default application
+   * (Finder / Explorer / xdg-open hand-off). The browser carrier restricts this
+   * privileged method to loopback, same-origin requests.
+   */
+  openPath(
+    request: RpcRequest<{ path: string }>,
+    signal: AbortSignal,
+  ): Promise<RpcResponse<{ opened: true }>>
 }

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

@@ -27,11 +27,11 @@ export interface ApiProxy {
 // ---- Domain interfaces and payload entities ----
 export type {
   HistoryEntry, ModelCatalogFailure, ModelCatalogModel, ModelProviderGroup, ModelReasoning,
-  ModelReasoningEffort, ModelTarget, SessionModels, SessionsApi, SessionSummary,
+  ModelReasoningEffort, ModelTarget, SessionModels, SessionProjectionsBlock, SessionsApi, SessionSummary,
 } from './sessions.ts'
 export type { HostApi } from './host.ts'
 export type { WorkspaceApi, WorkspaceId, WorkspaceView } from './workspace.ts'
-export type { CommandsApi, CommandDescriptor, CommandExecuteResult } from './commands.ts'
+export type { CommandsApi, CommandDescriptor } from './commands.ts'
 export type { SkillsApi, SkillEntry } from './skills.ts'
 export type { EventsApi, MuxFrame, HostFrame, ToolCallView, ToolEventView, ToolResultView } from './events.ts'
 export type { ApprovalResponsePayload } from './approvals.ts'

packages/host/apiproxy/src/api/rpc-map.ts

@@ -26,6 +26,7 @@ export interface RpcMethodMap {
   'session.cancel': SessionsApi['cancel']
   'host.describe': HostApi['describe']
   'host.pickDirectory': HostApi['pickDirectory']
+  'host.openPath': HostApi['openPath']
   'workspace.list': WorkspaceApi['list']
   'workspace.create': WorkspaceApi['create']
   'workspace.rename': WorkspaceApi['rename']

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

@@ -11,7 +11,7 @@ import type { RequestPayload, ResponseValue } from './rpc-map.ts'
 import type { Wire } from './rpc.schema.ts'
 import type {
   HistoryEntry, ModelCatalogFailure, ModelCatalogModel, ModelProviderGroup, ModelReasoning,
-  ModelReasoningEffort, ModelTarget, SessionSummary,
+  ModelReasoningEffort, ModelTarget, SessionProjectionsBlock, SessionSummary,
 } from './sessions.ts'
 import type { ToolEventView } from './events.ts'
 import type { WorkspaceId } from './workspace.ts'
@@ -139,17 +139,22 @@ export const historyEntrySchema = z.object({
   view: toolEventViewSchema.optional(),
 }) satisfies z.ZodType<Wire<HistoryEntry>>
 
-/** One todo item of the tail page's session-level projection (the todo/write payload shape). */
-export const todoItemSchema = z.object({
-  content: z.string(),
-  status: z.union([z.literal('pending'), z.literal('in_progress'), z.literal('completed')]),
-})
+/**
+ * Projection baseline passthrough: `values` stays a wide record — each value
+ * was already parsed by its provider's own schema on the host side, and
+ * deep-validating here would import every domain's schema into the carrier.
+ */
+export const sessionProjectionsBlockSchema = z.object({
+  // -1 = empty log (the lastSeq convention of session/subscribed).
+  asOfSeq: z.number().int().min(-1),
+  values: z.record(z.string(), z.unknown()),
+}) as unknown as z.ZodType<SessionProjectionsBlock>
 
-/** session.history response value. */
+/** session.history response value (projections rides the tail page only). */
 export const sessionHistoryValueSchema = z.object({
   events: z.array(historyEntrySchema),
   hasMore: z.boolean(),
-  todos: z.array(todoItemSchema).optional(),
+  projections: sessionProjectionsBlockSchema.optional(),
 }) satisfies z.ZodType<Wire<ResponseValue<'session.history'>>>
 
 /** session.models request payload. */

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

@@ -5,7 +5,10 @@
  */
 
 import type { ContentBlock } from '@deepseek-ai/dsh-llm/types'
-import type { SessionEvent, SessionId, TodoItem } from '@deepseek-ai/dsh-session/types'
+import type { SessionEvent, SessionId } from '@deepseek-ai/dsh-session/types'
+// The pure-type outlet: api/ is browser-importable, and the package root's
+// cordis Context merge (via dsh-agent) must not enter client aggregates.
+import type { SessionProjectionMap } from '@deepseek-ai/dsh-session-projection/types'
 import type { RpcId, RpcRequest, RpcResponse } from './rpc.ts'
 import type { ToolEventView } from './events.ts'
 import type { WorkspaceId } from './workspace.ts'
@@ -32,6 +35,23 @@ export interface HistoryEntry {
   view?: ToolEventView
 }
 
+/**
+ * The projection baseline riding the history tail page: one synchronous cut
+ * over every registered projection unit, read from the registry's watermark
+ * cache. `asOfSeq` is the seq of the last committed event every value
+ * reflects — the window tail event seq (`-1` for an empty log, mirroring
+ * `session/subscribed.lastSeq`), directly comparable with
+ * `session/projection` frame seqs under the client's higher-seq-wins rule. A
+ * key absent from `values` means the capability is absent (its domain plugin
+ * is unmounted).
+ */
+export interface SessionProjectionsBlock {
+  /** Seq of the last event the values reflect; -1 for an empty log. */
+  asOfSeq: number
+  /** Whole current value per registered projection key. */
+  values: Partial<SessionProjectionMap>
+}
+
 /** Complete model target selected for one session. */
 export interface ModelTarget {
   /** Registered provider route. */
@@ -149,13 +169,14 @@ 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).
+   * The tail page — and only the tail page — additionally carries `projections`
+   * when the deployment mounts the session-projection registry: every moment
+   * the client needs a fresh baseline already pulls the tail page, and
+   * loadOlder (the only beforeSeq path) is the only path that never needs one.
+   * A deployment without the registry serves histories without the block.
    */
   history(request: RpcRequest<{ sessionId: SessionId; beforeSeq?: number; maxMessages?: number }>):
-  Promise<RpcResponse<{ events: HistoryEntry[]; hasMore: boolean; todos?: TodoItem[] }>>
+  Promise<RpcResponse<{ events: HistoryEntry[]; hasMore: boolean; projections?: SessionProjectionsBlock }>>
 
   /** Reads a fresh advisory model directory for this session. Provider lookups run independently. */
   models(request: RpcRequest<{ sessionId: SessionId }>): Promise<RpcResponse<SessionModels>>

packages/host/apiproxy/src/fetch/client.ts

@@ -13,7 +13,9 @@ import { RpcId } from '../api/rpc.ts'
 import type { Wire } from '../api/rpc.schema.ts'
 import { rpcReceiptSchema, serverRequestSchema, serverResponseSchema } from '../api/rpc.schema.ts'
 import { hostFrameSchema, muxFrameSchema } from '../api/events.schema.ts'
-import { hostDescribeValueSchema, hostPickDirectoryValueSchema } from '../api/host.schema.ts'
+import {
+  hostDescribeValueSchema, hostOpenPathValueSchema, hostPickDirectoryValueSchema,
+} from '../api/host.schema.ts'
 import {
   sessionCancelValueSchema,
   sessionCreateValueSchema,
@@ -61,6 +63,7 @@ export interface IApiClient {
   host: {
     describe(payload: RequestPayload<'host.describe'>, signal?: AbortSignal): Promise<RpcResponse<ResponseValue<'host.describe'>>>
     pickDirectory(payload: RequestPayload<'host.pickDirectory'>, signal?: AbortSignal): Promise<RpcResponse<ResponseValue<'host.pickDirectory'>>>
+    openPath(payload: RequestPayload<'host.openPath'>, signal?: AbortSignal): Promise<RpcResponse<ResponseValue<'host.openPath'>>>
   }
   workspace: {
     list(payload: RequestPayload<'workspace.list'>, signal?: AbortSignal): Promise<RpcResponse<ResponseValue<'workspace.list'>>>
@@ -98,6 +101,7 @@ const UNARY_VALUE_SCHEMAS: { [K in keyof RpcMethodMap]: z.ZodType<Wire<ResponseV
   'session.cancel': sessionCancelValueSchema,
   'host.describe': hostDescribeValueSchema,
   'host.pickDirectory': hostPickDirectoryValueSchema,
+  'host.openPath': hostOpenPathValueSchema,
   'workspace.list': workspaceListValueSchema,
   'workspace.create': workspaceCreateValueSchema,
   'workspace.rename': workspaceRenameValueSchema,
@@ -305,6 +309,7 @@ export abstract class AbstractApiClient implements IApiClient {
     // A native system dialog is user-paced and may legitimately stay open
     // longer than the normal unary deadline. Caller/connection aborts remain.
     pickDirectory: (payload, signal) => this.callUnary('host.pickDirectory', payload, signal, false),
+    openPath: (payload, signal) => this.callUnary('host.openPath', payload, signal),
   }
 
   readonly workspace: IApiClient['workspace'] = {

packages/host/apiproxy/src/fetch/handler.ts

@@ -23,7 +23,9 @@ import {
   sessionPromptRequestSchema,
   sessionSelectModelRequestSchema,
 } from '../api/sessions.schema.ts'
-import { hostDescribeRequestSchema, hostPickDirectoryRequestSchema } from '../api/host.schema.ts'
+import {
+  hostDescribeRequestSchema, hostOpenPathRequestSchema, hostPickDirectoryRequestSchema,
+} from '../api/host.schema.ts'
 import {
   workspaceCreateRequestSchema,
   workspaceDeleteRequestSchema,
@@ -60,6 +62,7 @@ const UNARY_ROUTES: UnaryRoutes = {
   'session.cancel': { schema: sessionCancelRequestSchema, invoke: (api, r) => api.sessions.cancel(r) },
   'host.describe': { schema: hostDescribeRequestSchema, invoke: (api, r) => api.host.describe(r) },
   'host.pickDirectory': { schema: hostPickDirectoryRequestSchema, invoke: (api, r, signal) => api.host.pickDirectory(r, signal) },
+  'host.openPath': { schema: hostOpenPathRequestSchema, invoke: (api, r, signal) => api.host.openPath(r, signal) },
   'workspace.list': { schema: workspaceListRequestSchema, invoke: (api, r) => api.workspace.list(r) },
   'workspace.create': { schema: workspaceCreateRequestSchema, invoke: (api, r) => api.workspace.create(r) },
   'workspace.rename': { schema: workspaceRenameRequestSchema, invoke: (api, r) => api.workspace.rename(r) },

packages/host/apiproxy/src/native-command.ts

@@ -0,0 +1,38 @@
+/** Shared no-shell `execFile` runner for native host dialogs and openers. */
+
+import { execFile } from 'node:child_process'
+
+/** Testable command boundary; native implementations never invoke a shell. */
+export type NativeCommandRunner = (
+  command: string,
+  args: readonly string[],
+  signal: AbortSignal,
+) => Promise<{ stdout: string; stderr: string }>
+
+/**
+ * Run a host command with utf8 stdio, abort propagation, and Windows hide.
+ * @param command - executable path or PATH name.
+ * @param args - argv (never a shell string).
+ * @param signal - caller/connection lifetime; abort terminates the child.
+ * @returns captured stdout/stderr on exit 0.
+ */
+export const runNativeCommand: NativeCommandRunner = (command, args, signal) =>
+  new Promise((resolve, reject) => {
+    execFile(
+      command,
+      [...args],
+      { encoding: 'utf8', signal, windowsHide: true },
+      (error, stdout, stderr) => {
+        if (error !== null) {
+          const failure = Object.assign(new Error(error.message, { cause: error }), {
+            code: error.code,
+            stdout,
+            stderr,
+          })
+          reject(failure)
+          return
+        }
+        resolve({ stdout, stderr })
+      },
+    )
+  })

packages/host/apiproxy/src/native-directory-picker.ts

@@ -1,13 +1,9 @@
 /** Cross-platform native single-directory picker used by the local GUI carrier. */
 
-import { execFile } from 'node:child_process'
+import { runNativeCommand, type NativeCommandRunner } from './native-command.ts'
 
 /** Testable command boundary; native implementations never invoke a shell. */
-export type DirectoryPickerRunner = (
-  command: string,
-  args: readonly string[],
-  signal: AbortSignal,
-) => Promise<{ stdout: string; stderr: string }>
+export type DirectoryPickerRunner = NativeCommandRunner
 
 /** Injectable platform facts for deterministic adapter tests. */
 export interface DirectoryPickerInternals {
@@ -15,27 +11,6 @@ export interface DirectoryPickerInternals {
   run?: DirectoryPickerRunner
 }
 
-const runCommand: DirectoryPickerRunner = (command, args, signal) =>
-  new Promise((resolve, reject) => {
-    execFile(
-      command,
-      [...args],
-      { encoding: 'utf8', signal, windowsHide: true },
-      (error, stdout, stderr) => {
-        if (error !== null) {
-          const failure = Object.assign(new Error(error.message, { cause: error }), {
-            code: error.code,
-            stdout,
-            stderr,
-          })
-          reject(failure)
-          return
-        }
-        resolve({ stdout, stderr })
-      },
-    )
-  })
-
 function outputPath(stdout: string): string | null {
   const path = stdout.replace(/[\r\n]+$/, '')
   return path === '' ? null : path
@@ -72,7 +47,7 @@ export async function pickNativeDirectory(
   internals: DirectoryPickerInternals = {},
 ): Promise<string | null> {
   const platform = internals.platform ?? process.platform
-  const run = internals.run ?? runCommand
+  const run = internals.run ?? runNativeCommand
 
   if (platform === 'darwin') {
     try {

packages/host/apiproxy/src/native-path-opener.ts

@@ -0,0 +1,53 @@
+/** Cross-platform open-with-default-application used by the local GUI carrier. */
+
+import { runNativeCommand, type NativeCommandRunner } from './native-command.ts'
+
+/** Testable command boundary; native implementations never invoke a shell. */
+export type PathOpenerRunner = NativeCommandRunner
+
+/** Injectable platform facts for deterministic adapter tests. */
+export interface PathOpenerInternals {
+  platform?: NodeJS.Platform
+  run?: PathOpenerRunner
+}
+
+/** PowerShell single-quoted literal (doubles embedded quotes). */
+function powershellLiteral(path: string): string {
+  return `'${path.replace(/'/g, "''")}'`
+}
+
+/**
+ * Open a filesystem path with the operating system's default application.
+ * @param path - absolute or host-resolvable path (caller owns resolution).
+ * @param signal - caller/connection lifetime; abort terminates the native command.
+ * @param internals - platform and runner seam for deterministic tests.
+ */
+export async function openNativePath(
+  path: string,
+  signal: AbortSignal,
+  internals: PathOpenerInternals = {},
+): Promise<void> {
+  const platform = internals.platform ?? process.platform
+  const run = internals.run ?? runNativeCommand
+
+  if (platform === 'darwin') {
+    await run('open', [path], signal)
+    return
+  }
+
+  if (platform === 'win32') {
+    await run('powershell.exe', [
+      '-NoProfile',
+      '-Command',
+      `Invoke-Item -LiteralPath ${powershellLiteral(path)}`,
+    ], signal)
+    return
+  }
+
+  if (platform === 'linux') {
+    await run('xdg-open', [path], signal)
+    return
+  }
+
+  throw new Error(`native path opener is unsupported on ${platform}`)
+}