fix(web): stabilize nested subagent navigation

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

@@ -55,6 +55,11 @@ export interface SubagentCatalogSnapshot extends SubagentCatalog {
   error: RpcError | null
 }
 
+interface CatalogInflight {
+  readonly promise: Promise<void>
+  readonly expandableRows: Set<SessionId>
+}
+
 type SessionListMutation =
   | { kind: 'upsert'; summary: SessionSummary }
   | { kind: 'remove'; sessionId: SessionId }
@@ -94,7 +99,7 @@ export class SessionManager {
   private listMutations: SessionListMutation[] | null = null
   private readonly addresses = new Map<SessionId, SubagentAddress>()
   private readonly catalogs = new Map<SessionId, SubagentCatalogSnapshot>()
-  private readonly catalogInflight = new Map<SessionId, Promise<void>>()
+  private readonly catalogInflight = new Map<SessionId, CatalogInflight>()
   private readonly openCatalogs = new Set<SessionId>()
   private readonly catalogDebounce = new Map<SessionId, ReturnType<typeof setTimeout>>()
 
@@ -131,10 +136,11 @@ export class SessionManager {
    * @param sessionId - listed or catalog-addressed Session id.
    */
   select(sessionId: SessionId): void {
-    const address = this.addresses.get(sessionId)
+    const address = this.navigationAddress(sessionId)
     if (!this.summaries.some(summary => summary.sessionId === sessionId) && address === undefined) {
       throw new Error(`sessions.select: unknown session ${sessionId}`)
     }
+    if (address !== undefined) this.addresses.set(sessionId, address)
     this.sessions.get(sessionId)?.configureSubagent(
       address,
       address === undefined
@@ -178,6 +184,23 @@ export class SessionManager {
     return this.addresses.get(sessionId)
   }
 
+  /**
+   * Resolve an address for breadcrumb navigation without retaining transport authority.
+   * @param sessionId - possible child id in an already-loaded catalog.
+   * @returns A retained or catalog-derived direct-parent address.
+   */
+  navigationAddress(sessionId: SessionId): SubagentAddress | undefined {
+    const retained = this.addresses.get(sessionId)
+    if (retained !== undefined) return retained
+    for (const [parentSessionId, catalog] of this.catalogs) {
+      const child = catalog.entries.find(entry => entry.kind === 'child' && entry.id === sessionId)
+      if (child?.kind === 'child') {
+        return { parentSessionId, childSessionId: sessionId, mode: child.mode }
+      }
+    }
+    return undefined
+  }
+
   // ---- Instance management ----
 
   /**
@@ -262,8 +285,9 @@ export class SessionManager {
    */
   refreshSubagents(parentSessionId: SessionId): Promise<void> {
     const existing = this.catalogInflight.get(parentSessionId)
-    if (existing !== undefined) return existing
+    if (existing !== undefined) return existing.promise
     const previous = this.catalogs.get(parentSessionId)
+    const expandableRows = new Set<SessionId>()
     this.catalogs.set(parentSessionId, {
       entries: previous?.entries ?? [],
       parentAvailable: previous?.parentAvailable ?? false,
@@ -277,6 +301,7 @@ export class SessionManager {
         if (result.ok) {
           this.catalogs.set(parentSessionId, {
             ...result.value,
+            entries: this.withExpandableRows(result.value.entries, expandableRows),
             state: 'ready',
             error: null,
           })
@@ -286,7 +311,7 @@ export class SessionManager {
           }
         } else {
           this.catalogs.set(parentSessionId, {
-            entries: previous?.entries ?? [],
+            entries: this.withExpandableRows(previous?.entries ?? [], expandableRows),
             parentAvailable: previous?.parentAvailable ?? false,
             state: 'error',
             error: result.error,
@@ -295,7 +320,7 @@ export class SessionManager {
       } catch (error: unknown) {
         const folded = transportError<never>(error)
         this.catalogs.set(parentSessionId, {
-          entries: previous?.entries ?? [],
+          entries: this.withExpandableRows(previous?.entries ?? [], expandableRows),
           parentAvailable: previous?.parentAvailable ?? false,
           state: 'error',
           error: folded.ok ? null : folded.error,
@@ -305,7 +330,7 @@ export class SessionManager {
         this.notifier.markDirty()
       }
     })()
-    this.catalogInflight.set(parentSessionId, operation)
+    this.catalogInflight.set(parentSessionId, { promise: operation, expandableRows })
     return operation
   }
 
@@ -717,8 +742,14 @@ export class SessionManager {
     if (changed) this.notifier.markDirty()
   }
 
-  /** Mark a loaded parent row expandable after one direct subagent publishes. */
+  /** Preserve and project a positive expandability hint after one direct subagent publishes. */
   private markCatalogParentExpandable(parentSessionId: SessionId): void {
+    this.applyCatalogParentExpandable(parentSessionId)
+    for (const inflight of this.catalogInflight.values()) inflight.expandableRows.add(parentSessionId)
+  }
+
+  /** Apply one positive expandability hint to every loaded catalog containing that unique row id. */
+  private applyCatalogParentExpandable(parentSessionId: SessionId): void {
     let changed = false
     for (const [catalogParentId, catalog] of this.catalogs) {
       if (!catalog.entries.some(entry =>
@@ -733,6 +764,16 @@ export class SessionManager {
     if (changed) this.notifier.markDirty()
   }
 
+  /** Fold request-local positive row mutations into one catalog result before publication. */
+  private withExpandableRows(
+    entries: SubagentCatalog['entries'],
+    expandableRows: ReadonlySet<SessionId>,
+  ): SubagentCatalog['entries'] {
+    return entries.map(entry => entry.kind === 'child' && expandableRows.has(entry.id)
+      ? { ...entry, hasChildren: true }
+      : entry)
+  }
+
   private buildListSnapshot(): SessionListSnapshot {
     const merged: TitledSessionSummary[] = this.summaries.map((summary) => {
       // List rows read the generic 'title' projection key (host-computed unit

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

@@ -4,7 +4,7 @@
  * session-scoped surface keys off — migrated here from ui-layout per the
  * slot-parity design), Agent scope tree (mintScope pattern: no-op plugin
  * Fiber + ctx.extend scope tag; one scope per session, agent id === session
- * id), stable SessionBinding cache, ancestry walk.
+ * id), stable SessionBinding cache, breadcrumb-route projection.
  *
  * Scope lifecycle is stage-driven: a scope is minted lazily on first
  * resolution (pure — resolution has no side effects and is render-safe);
@@ -206,7 +206,7 @@ export interface SessionProvideDescriptor {
   resolve(binding: SessionBinding): SessionProvideContribution
 }
 
-/** Root sessions service: list store, current selection, object-layer manager, scope tree, bindings, ancestry. */
+/** Root sessions service: list store, current selection, object-layer manager, scope tree, bindings, and breadcrumb routes. */
 export class SessionsService implements ISessions {
   /**
    * The wire schema's own result bound, re-exposed for presentation plugins as
@@ -563,25 +563,6 @@ export class SessionsService implements ISessions {
     }
   }
 
-  /**
-   * Breadcrumb feed: walk subagent parent links inside the list store.
-   * @param id - session id.
-   * @returns The ordinary owner plus its subagent route, or only the requested ordinary/fork session.
-   */
-  ancestry(id: SessionId): SessionSummary[] {
-    const { byId } = this.list.getSnapshot()
-    const chain: SessionSummary[] = []
-    let cursor: SessionId | undefined = id
-    while (cursor !== undefined) {
-      const summary: SessionSummary | undefined = byId[cursor]
-      if (summary === undefined || chain.includes(summary)) break
-      chain.unshift(summary)
-      if (summary.origin !== 'subagent') break
-      cursor = summary.parentId
-    }
-    return chain
-  }
-
   /**
    * Lazily mint the scope + binding for an eligible session. Eligibility and
    * prune share one predicate (decision 12): listed on the host or selected
@@ -660,7 +641,7 @@ export class SessionsService implements ISessions {
           }
         }
         if (byId[address.parentSessionId] !== undefined) break
-        address = this.manager.subagentAddress(address.parentSessionId)
+        address = this.manager.navigationAddress(address.parentSessionId)
       }
     }
     const persisted = this.selection.getSnapshot().sessionId