The Desktop GUI (tui_gateway) slash worker subprocess has no reader for
the CLI's _pending_input queue. /learn's CLI handler prints the ack and
puts the built prompt onto that queue, so in the TUI the prompt was
silently dropped — ack shown, no LLM turn, no skill created (#51829).
command.dispatch already handles 'learn' correctly (returns
{type: send, message: build_learn_prompt(arg)}), but 'learn' was missing
from _PENDING_INPUT_COMMANDS, so slash.exec fell through to the worker
instead of routing to command.dispatch. Add it to the frozenset, matching
the existing goal/queue/steer/plan pattern.
a4fa1481e2