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/state.ts

@@ -61,8 +61,9 @@ export interface ReconciledInstructionContext {
   versionUpdates: InstructionVersionUpdate[]
 }
 
-/** Plugin-owned context with required replay metadata. */
+/** Plugin-owned raw context with required replay metadata. */
 export interface WorkspaceHookContext extends HookContext {
+  envelope: 'raw'
   meta: JsonValue
 }
 
@@ -75,7 +76,7 @@ function workspaceContextHook(text: string, changes: WorkspaceInstructionChange[
     ...change.digest !== undefined ? { digest: change.digest } : {},
   }))
   const meta: JsonValue = { kind: 'workspace-instructions', version: 1, changes: serializedChanges }
-  return { content: [{ type: 'text', text }], source: PLUGIN_SOURCE, meta }
+  return { content: [{ type: 'text', text }], source: PLUGIN_SOURCE, envelope: 'raw', meta }
 }
 
 /**