feat(session-query): checkpoint build round 1

packages/core/session/src/index.ts

@@ -20,8 +20,8 @@ export * from './types.ts'
 export { isJsonValue } from './json.ts'
 export type { JsonValue } from './json.ts'
 export { interruptedTurnClosers } from './repair.ts'
-export type { SurfaceNode } from './surface.ts'
-export { isSurfaceEvent, isSurfaceEligibleType } from './surface.ts'
+export type { SurfaceFoldReplacement, SurfaceFoldResult, SurfaceNode } from './surface.ts'
+export { foldSurface, isSurfaceEvent, isSurfaceEligibleType } from './surface.ts'
 export { isToolPairingBalanced } from './tool-pairing.ts'
 export { applyHeaderDelta, canonicalHeader, diffHeader, foldRequestHeader, headerEquals } from './request-header.ts'
 
@@ -37,6 +37,14 @@ declare module 'cordis' {
      * @mode emit
      */
     'session/created'(session: Session): void
+    /**
+     * A session left the live store. The header is snapshotted after the store
+     * entry is removed; listener failures are contained and cannot break the
+     * owning fiber's teardown.
+     * @param header - immutable identity and lineage of the removed session.
+     * @mode parallel
+     */
+    'session/removed'(header: SessionHeader): Promise<void> | void
     /**
      * An event was appended to a session log (sync, fire-and-forget). This is
      * the per-append feed a UI or invariant plugin tails.
@@ -501,8 +509,15 @@ export class SessionStore extends Service {
     session.onAppend = (event) => { this.ctx.emit('session/event', session, event) }
     this.store.set(session.id, session)
     return () => {
+      if (this.store.get(session.id) !== session) return
       session.onAppend = undefined
       this.store.delete(session.id)
+      const header = structuredClone(session.header)
+      void Promise.resolve()
+        .then(() => this.ctx.parallel('session/removed', header))
+        .catch((error: unknown) => {
+          this.ctx.logger.warn(`session store: session/removed listener failed for "${session.id}": ${String(error)}`)
+        })
     }
   }