…21910)

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.

Extends the existing /undo command from a single in-memory exchange
removal into a full rewind: back up N user turns (default 1), soft-delete
the truncated rows in SessionDB (active=0, kept for audit, hidden from
re-prompts and search), notify memory providers, and prefill the composer
with the backed-up message text for editing — CLI and TUI.

Reuses the SessionDB rewind primitives, the on_session_switch(rewound=True)
memory hook, and the TUI command.dispatch prefill payload from SaguaroDev's
#21910 work, wired to /undo [N] instead of a separate /rewind picker.

- cli.py: undo_last(n, prefill) — in-memory truncate + SQLite soft-delete
  + agent surgery (system-prompt invalidate, flush-index reset) + memory
  notify + editable buffer prefill; /undo dispatch parses optional count;
  checkpoint-rollback caller passes prefill=False
- tui_gateway/server.py: command.dispatch undo branch (was rewind) parses
  count, picks Nth-from-last user turn, clamps to oldest
- commands.py: /undo gains [N] args_hint
- tests: rename + expand TUI suite (multi-turn, clamp, invalid-count)
- release.py: AUTHOR_MAP entry for SaguaroDev

Co-authored-by: SaguaroDev <74339271+SaguaroDev@users.noreply.github.com>

The on_session_switch fan-out passed rewound=rewound unconditionally,
injecting rewound=False into every provider's **kwargs on the common
/resume, /branch, /new, and compression paths. Providers that capture
extra kwargs into an 'extra' dict (and the exact-dict-equality tests
guarding them) broke. Forward rewound only when truthy; /undo sets it
explicitly, everyone else stays clean.