chore(vendor): import pi 0.85.1

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

third_party/pi/packages/coding-agent/src/experimental/services/sessions.ts

@@ -0,0 +1,35 @@
+import { type Context, defineService, type ReplicatedState } from "@earendil-works/chord";
+import type { ServerId } from "@earendil-works/pi-protocol";
+
+export interface SessionAddress {
+	serverId: ServerId;
+	sessionId: string;
+}
+
+export interface SessionSummary extends SessionAddress {
+	createdAt: number;
+}
+
+export interface SessionCreateOptions {
+	id?: string;
+}
+
+export interface SessionDirectoryState {
+	revision: number;
+	sessions: SessionSummary[];
+}
+
+export interface SessionDirectory {
+	readonly state: ReplicatedState<SessionDirectoryState>;
+}
+
+export const SessionDirectory = defineService<SessionDirectory>("pi.session-directory");
+
+export interface SessionManagement {
+	create(options: SessionCreateOptions, context: Context): Promise<SessionSummary>;
+	remove(sessionId: string, context: Context): Promise<void>;
+	attach(sessionId: string, context: Context): Promise<void>;
+	detach(context: Context): Promise<void>;
+}
+
+export const SessionManagement = defineService<SessionManagement>("pi.session-management");