/planmode command works in non-Claude engine chats with Claude-specific output

[nathanschram]

Bug

/planmode and /planmode off work in Codex (and presumably other non-Claude) engine chats, producing Claude-specific output referencing --permission-mode plan and --permission-mode acceptEdits flags that don't apply to Codex.

Reproduction

1. Open the Codex engine chat (ut-dev: codex)
2. Send /planmode
3. Response: plan mode on for this chat. new sessions will use --permission-mode plan.
4. Send /planmode off
5. Response: plan mode off for this chat. new sessions will use --permission-mode acceptEdits.

Expected

Either:

• a) /planmode is disabled for non-Claude engines and responds with "Plan mode is only available for Claude Code" or similar
• b) The command is engine-aware and shows the equivalent for each engine (e.g. for Codex: approval policy full auto/safe)

Context

• The /config home page correctly shows "Approval policy" instead of "Plan mode" for Codex
• But the standalone /planmode command doesn't check the current engine — it always applies Claude Code permission mode logic
• --permission-mode plan and --permission-mode acceptEdits are Claude Code CLI flags; Codex uses --ask-for-approval never|untrusted instead
• Setting plan mode in a Codex chat could silently pass invalid flags to the Codex CLI, or be silently ignored — either way it's confusing

Affected files

• src/untether/telegram/commands/planmode.py — PlanModeCommand doesn't check engine type
• The /config UI correctly gates this (shows "Approval policy" for Codex), but the standalone command bypasses that gate

Version

v0.35.0rc11 — found during Codex integration testing