refactor(session): open journal streams from snapshots

packages/api/session-controller/src/client/contract/snapshot.ts

@@ -29,7 +29,11 @@ export interface SessionSnapshot {
   readonly sessionId: SessionId
   readonly queue: readonly QueuedMessage[]
   readonly running: boolean
-  readonly subagent: { readonly address: SubagentAddress; readonly parentAvailable: boolean } | null
+  readonly subagent: {
+    readonly address: SubagentAddress
+    /** Absent until the direct-parent catalog resolves. */
+    readonly parentAvailable?: boolean
+  } | null
   readonly removed: boolean
   readonly openState: OpenState
   readonly openError: ClientFailure | null

packages/api/session-controller/src/client/sessions/session.ts

@@ -45,7 +45,7 @@ export const PAGE_MESSAGES = 50
 export interface SessionOptions {
   /** Catalog-discovered address selecting non-activating subagent transport. */
   address?: SubagentAddress
-  /** Whether the exact direct parent Agent was live at the latest catalog read. */
+  /** Whether the exact direct parent Agent was live at the latest catalog read; absent before that read. */
   parentAvailable?: boolean
   /**
    * First ACCEPTED prompt on a blank session (fires at most once, on the
@@ -86,7 +86,7 @@ export class Session implements SessionFace {
   private readonly queueMirror = new SessionQueueMirror()
   private running = false
   private address: SubagentAddress | undefined
-  private parentAvailable = false
+  private parentAvailable: boolean | undefined
   /**
    * Sticky send marker, private input of the composerPhase derivation: set
    * synchronously before prompt()'s first await, never reset — the blank →
@@ -144,7 +144,7 @@ export class Session implements SessionFace {
   ) {
     this.projections = options.projections ?? new ProjectionValueStore()
     this.address = options.address
-    this.parentAvailable = options.parentAvailable ?? false
+    this.parentAvailable = options.parentAvailable
     this.notifier = new Notifier(() => {
       this.snapshotCache = this.buildSnapshot()
     })
@@ -467,9 +467,9 @@ export class Session implements SessionFace {
    * Install or clear the catalog-discovered transport address. A changed
    * address rebuilds an already-open window through its new history route.
    * @param address - direct parent/child address, or undefined for ordinary transport.
-   * @param parentAvailable - latest exact-parent availability hint.
+   * @param parentAvailable - latest exact-parent availability hint, or undefined before a catalog read.
    */
-  configureSubagent(address: SubagentAddress | undefined, parentAvailable = false): void {
+  configureSubagent(address: SubagentAddress | undefined, parentAvailable?: boolean): void {
     const same = this.address?.parentSessionId === address?.parentSessionId
       && this.address?.childSessionId === address?.childSessionId
       && this.address?.mode === address?.mode
@@ -623,7 +623,10 @@ export class Session implements SessionFace {
       running: this.running,
       subagent: this.address === undefined
         ? null
-        : { address: this.address, parentAvailable: this.parentAvailable },
+        : {
+          address: this.address,
+          ...(this.parentAvailable === undefined ? {} : { parentAvailable: this.parentAvailable }),
+        },
       removed: this.removed,
       openState: this.openState,
       openError: this.openError,

packages/api/session-controller/src/client/transport.ts

@@ -17,6 +17,7 @@ import type {
   SessionEventEntry,
   SessionPage,
   SessionPageRequest,
+  SessionProjectionBaseline,
 } from '../types.ts'
 
 export {
@@ -30,8 +31,13 @@ export type ClientSessionPageRequest = Omit<SessionPageRequest, 'address' | 'thr
 /** Complete generated `ctx.remote.session` namespace. */
 export type SessionRemote = ClientRemote['session']
 
+/** Opening metadata carried only by a follow snapshot, never by loadOlder pages. */
+interface SessionJournalPage extends SessionPage {
+  readonly projections?: SessionProjectionBaseline
+}
+
 /** One complete publication from the Session journal stream. */
-export type SessionJournalChange = RemoteJournalChange<SessionPage, SessionEventEntry>
+export type SessionJournalChange = RemoteJournalChange<SessionJournalPage, SessionEventEntry>
 
 type SessionControlBaselineFrame = Extract<SessionControlFrame, { type: 'baseline' }>
 type SessionControlDeltaFrame = Exclude<SessionControlFrame, SessionControlBaselineFrame>
@@ -93,7 +99,7 @@ export function createSessionControlStream(
 
 /** Gateway-owned event journal bound to one ordinary or direct-subagent Session address. */
 export class SessionEventStream extends RemoteJournalStream<
-  SessionPage,
+  SessionJournalPage,
   SessionEventEntry,
   number,
   ClientSessionPageRequest
@@ -126,15 +132,23 @@ export class SessionEventStream extends RemoteJournalStream<
 
   /** @inheritdoc */
   protected override async * follow(
-    afterSeq: number | undefined,
+    request: ClientSessionPageRequest,
     signal: AbortSignal,
-  ): AsyncIterable<RemoteJournalFrame<SessionEventEntry, number>> {
-    const request = afterSeq === undefined
-      ? { address: this.address }
-      : { address: this.address, afterSeq }
-    for await (const frame of this.remote.session.follow(request, signal)) {
-      if (frame.type === 'opened') {
-        yield frame
+  ): AsyncIterable<RemoteJournalFrame<SessionEventEntry, number, SessionJournalPage>> {
+    for await (const frame of this.remote.session.follow({
+      address: this.address,
+      ...(request.maxMessages === undefined ? {} : { maxMessages: request.maxMessages }),
+    }, signal)) {
+      if (frame.type === 'snapshot') {
+        yield {
+          type: 'opened',
+          cursor: frame.cursor,
+          page: {
+            events: frame.events,
+            hasMore: frame.hasMore,
+            projections: frame.projections,
+          },
+        }
         continue
       }
       const { type: _type, ...entry } = frame
@@ -147,7 +161,7 @@ export class SessionEventStream extends RemoteJournalStream<
     request: ClientSessionPageRequest,
     throughSeq: number,
     signal: AbortSignal,
-  ): Promise<SessionPage> {
+  ): Promise<SessionJournalPage> {
     const result = await this.remote.session.page(
       { address: this.address, throughSeq, ...request },
       signal,