Merge remote-tracking branch 'origin/doc/host-client-group-readmes' into feat/directory-picker

# Conflicts:
#	packages/host/apiproxy/package.json
#	pnpm-lock.yaml

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

@@ -44,6 +44,10 @@ export interface RpcErrorDetailsMap {
   'directory-create-failed': { path: string }
   'directory-picker-unavailable': { capability: string }
   'agent-busy': { reason: string }
+  /** A known slash command reported a usage/state error; the message is the command's own text. */
+  'command-error': {}
+  /** A leading-/ prompt named no registered command; the message names the token. */
+  'unknown-command': {}
   'internal': {}
 }