feat(apiproxy): workspace.archiveSession RPC and archived-sessions frame

workspace.archiveSession answers the full updated archive set;
workspace.list carries the set as the reconnect baseline; the host
stream pushes host/archived-sessions-changed full snapshots from the
domain/changed global-put branch (same posture as workspace-changed).
Unknown sessions map to the existing session-not-found code.

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

@@ -71,6 +71,7 @@ export const hostFrameSchema = z.discriminatedUnion('type', [
   z.object({ type: z.literal('host/agent-error'), sessionId: sessionIdSchema, message: z.string() }),
   z.object({ type: z.literal('host/workspace-changed'), workspace: workspaceViewSchema }),
   z.object({ type: z.literal('host/workspace-removed'), workspaceId: workspaceIdSchema }),
+  z.object({ type: z.literal('host/archived-sessions-changed'), archivedSessionIds: z.array(sessionIdSchema) }),
   z.object({ type: z.literal('host/commands-changed') }),
   z.object({ type: z.literal('host/settings-changed'), ns: z.string() }),
   z.object({ type: z.literal('host/credentials-changed'), ref: z.string() }),

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

@@ -101,7 +101,9 @@ export type MuxFrame =
  * workspace mutation (create/attach/order change — the client upserts, while
  * `workspace.list` provides the reconnect baseline); workspace-removed is the
  * committed registration-deletion increment and never implies directory or
- * session-log deletion.
+ * session-log deletion; archived-sessions-changed pushes the full registry
+ * archive set after every durable change (same full-snapshot posture as
+ * workspace-changed — `workspace.list` re-baselines it on reconnect).
  */
 export type HostFrame =
   | { type: 'host/session-added'; sessionId: SessionId; blank: boolean; parentSessionId?: SessionId; cwd?: string }
@@ -110,6 +112,7 @@ export type HostFrame =
   | { type: 'host/agent-error'; sessionId: SessionId; message: string }
   | { type: 'host/workspace-changed'; workspace: WorkspaceView }
   | { type: 'host/workspace-removed'; workspaceId: WorkspaceView['workspaceId'] }
+  | { type: 'host/archived-sessions-changed'; archivedSessionIds: SessionId[] }
   /**
    * The command registry changed (`commands/change` passthrough). Pure
    * invalidation signal, no payload: clients refetch `command.list` in the

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

@@ -42,6 +42,7 @@ export interface RpcMethodMap {
   'workspace.rename': WorkspaceApi['rename']
   'workspace.delete': WorkspaceApi['delete']
   'workspace.insertSessionBefore': WorkspaceApi['insertSessionBefore']
+  'workspace.archiveSession': WorkspaceApi['archiveSession']
   'command.list': CommandsApi['list']
   'command.execute': CommandsApi['execute']
   'skill.list': SkillsApi['list']

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

@@ -28,6 +28,7 @@ export const workspaceListRequestSchema = z.object({}) satisfies z.ZodType<Wire<
 /** workspace.list response value. */
 export const workspaceListValueSchema = z.object({
   items: z.array(workspaceViewSchema),
+  archivedSessionIds: z.array(sessionIdSchema),
 }) satisfies z.ZodType<Wire<ResponseValue<'workspace.list'>>>
 
 /** workspace.create request payload: exactly one of path/name (the contract's create spellings). */
@@ -80,3 +81,13 @@ export const workspaceInsertSessionBeforeRequestSchema = z.object({
 export const workspaceInsertSessionBeforeValueSchema = z.object({
   workspace: workspaceViewSchema,
 }) satisfies z.ZodType<Wire<ResponseValue<'workspace.insertSessionBefore'>>>
+
+/** workspace.archiveSession request payload. */
+export const workspaceArchiveSessionRequestSchema = z.object({
+  sessionId: sessionIdSchema,
+}) satisfies z.ZodType<Wire<RequestPayload<'workspace.archiveSession'>>>
+
+/** workspace.archiveSession response value: the full updated archive set. */
+export const workspaceArchiveSessionValueSchema = z.object({
+  archivedSessionIds: z.array(sessionIdSchema),
+}) satisfies z.ZodType<Wire<ResponseValue<'workspace.archiveSession'>>>

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

@@ -37,8 +37,13 @@ export interface WorkspaceView {
 
 /** Workspace-domain unary methods (the map keys workspace.* of RpcMethodMap). */
 export interface WorkspaceApi {
-  /** Lists all workspaces in the registry's durable display order. */
-  list(request: RpcRequest<{}>): Promise<RpcResponse<{ items: WorkspaceView[] }>>
+  /**
+   * Lists all workspaces in the registry's durable display order, plus the
+   * registry-global archive set (the reconnect baseline of
+   * `host/archived-sessions-changed`). Archived sessions stay in their
+   * workspace's `sessionIds` account; grouping surfaces hide them.
+   */
+  list(request: RpcRequest<{}>): Promise<RpcResponse<{ items: WorkspaceView[]; archivedSessionIds: SessionId[] }>>
 
   /**
    * Creates (or idempotently resolves) a workspace. Exactly one of `path` /
@@ -86,4 +91,15 @@ export interface WorkspaceApi {
     sessionId: SessionId
     beforeSessionId?: SessionId
   }>): Promise<RpcResponse<{ workspace: WorkspaceView }>>
+
+  /**
+   * Adds one session to the registry-global archive set: the session
+   * disappears from every grouping surface but keeps its session log and its
+   * workspace accounting slot (a future unarchive restores its position).
+   * Idempotent for an already archived id. A session neither live nor in
+   * session persistence fails with `session-not-found`. Returns the full
+   * updated set (same snapshot the changed frame carries).
+   */
+  archiveSession(request: RpcRequest<{ sessionId: SessionId }>):
+  Promise<RpcResponse<{ archivedSessionIds: SessionId[] }>>
 }