tui: undo fails for admitted message after interrupt

Summary

Undo can fail with Message not found when the last visible user message was admitted while an assistant response was active, the response was interrupted, and the message has not yet been promoted into the materialized session history.

The TUI displays the admitted input immediately and selects it as the undo boundary, but the server's revert planner only searches promoted session_message rows. The message remains visible and is not undone.

Environment

• opencode version: 0.0.0-next-16542
• OS: macOS 25.5.0 (arm64)
• Terminal: Ghostty 1.3.1 (TERM_PROGRAM=ghostty, COLORTERM=truecolor)
• Shell: /bin/zsh
• Install/channel: next
• Active plugins: @warp-dot-dev/opencode-warp, @kitlangton/opencode-session-recap, a local debug workspace plugin, and a local voice plugin

Reproduction

1. Start an assistant response in the TUI.
2. While it is active, submit another user message so it is admitted as a steer.
3. Interrupt the active assistant response before the admitted message is promoted.
4. Run /undo while the admitted message is visible as the latest user message.
5. Observe that undo reports Message not found: <message ID> and does not revert the message.

Expected Behavior

Undo should work for the latest visible user message, or the TUI should avoid selecting an admitted-but-unpromoted input as a revert boundary. A visible message should not be offered as undoable if the server cannot resolve it.

Actual Behavior

The TUI selects the visible admitted input and calls session.revert.stage, but the server returns Message not found. No session.revert.staged event is written and the message remains in the conversation.

Additional Context

Observed once in session ses_0557f8315ffeqNZ6aWfs508uRA.

The failing boundary was msg_fb45655670010Crv5yk7d2Bpq6 ("Or maybe that doesn't make sense."). The preceding assistant message msg_fb4561fd8002ue3urmeD3LNWPj finished with Step interrupted.

Durable timeline:

18:43:04.679  session.input.admitted
                inputID=msg_fb45655670010Crv5yk7d2Bpq6
18:43:05.859  session.step.failed
                error.type=aborted, message="Step interrupted"
18:43:05.860  session.execution.interrupted
                reason=user
18:43:18.804  session.revert.stage requested
                messageID=msg_fb45655670010Crv5yk7d2Bpq6
                -> Message not found; no staged event persisted
18:43:47.057  session.input.promoted
                inputID=msg_fb45655670010Crv5yk7d2Bpq6

The client and server currently disagree during this window:

• packages/tui/src/context/data.tsx appends a user message to the visible message list on session.input.admitted.
• packages/tui/src/routes/session/index.tsx chooses the last visible user message for /undo.
• packages/core/src/session/revert.ts resolves the boundary only from session_message, where the input does not exist until session.input.promoted.

The installed CLI updated to 0.0.0-next-16543 afterward, but the elected service and failing session were running 0.0.0-next-16542.

A screenshot shows the affected user message followed by an interrupted assistant response.

Read packages/tui/src/context/data.tsx and packages/tui/src/routes/session/index.tsx to trace how admitted inputs become the undo boundary, then inspect packages/core/src/session/revert.ts to compare boundary resolution with session.input.promoted timing. Reproduce the interrupted-steer sequence and verify that /undo either resolves the visible message or does not offer it until the server can resolve it.