Adds the TUI half of the /rewind feature so the Ink terminal UI gets
the same affordance as the prompt_toolkit CLI.
Python side (tui_gateway/server.py):
- /rewind added to _PENDING_INPUT_COMMANDS so slash.exec rejects it
and the TUI falls through to command.dispatch (the only path with
access to live session state + memory hooks).
- New command.dispatch branch for name == "rewind":
v1 auto-picks the most recent user turn (Claude-Code-style single-
step undo), calls SessionDB.rewind_to_message, refreshes the
in-memory history, fires _memory_manager.on_session_switch with
rewound=True, and returns the new "prefill" payload.
- A dedicated picker overlay (multi-step rewind) is tracked as a
follow-up to #21910.
TS side (ui-tui/src/):
- New "prefill" variant on CommandDispatchResponse + asCommandDispatch
validator. Mirrors "send" but does NOT auto-submit; the client drops
the message into the composer for editing.
- createSlashHandler renders the optional notice via sys() and calls
ctx.composer.setInput(d.message), letting the user edit-and-resubmit
the rewound turn — the core UX promised by the issue.
Tests:
- 7 new tui_gateway tests covering prefill payload shape, in-memory
history truncation, DB soft-delete, memory-provider notification
(rewound=True), busy-session refusal, missing-session error, and
registry placement in _PENDING_INPUT_COMMANDS.
- Extended asCommandDispatch vitest covering the new prefill variant
(with + without notice, and rejection of malformed payloads).
Out of scope for v1 (tracked as #21910 follow-up):
- Dedicated picker overlay in Ink (the multi-step rewind UI). v1 auto-
picks the most recent user turn, matching the most common case.
- Gateway platforms (Telegram, Discord, etc.) — issue scopes v1 to
CLI + TUI only.
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