Retire the readline front door and the repl-agent example

Delete packages/ui/stdio and examples/repl-agent; rename stdio-demo to
@deepseek-ai/dsh-tui-demo (TUI-only, refuses pipes before Loader boot).
tui-agent owns the coding composition inline; echo-agent and the CI demo
smoke move to the one-shot cli-demo bin, which gains -p/--prompt. The
UI-independent with-key e2es move verbatim to tui-agent. SDK wizard's
'stdio' interface becomes 'tui'. PTY testing stays confined to TUI
surfaces; all other subprocess tests ride pipes.

See .agents/notes/implemented/simplification/2026-07-20-retire-readline-front-door.md

packages/context/workspace-context/src/index.ts

@@ -92,6 +92,7 @@ export function apply(ctx: Context, config: Config): void {
     if (update !== undefined) {
       agent.inject(update.context.content, {
         source: update.context.source,
+        envelope: update.context.envelope,
         meta: update.context.meta,
       })
       applyInstructionVersionUpdates(agent.session, update.versionUpdates, instructionVersions)