Function computeUndoCutoff

apps/vis/server/src/lib/context-projector.ts:682–698

Single source of truth for the `context.undo` backward walk, shared by both * projection modes. Mirrors agent-core `undo` (`agent/context/index.ts`): walk * from the end, skip `origin.kind === 'injection'` (those are KEPT even when * they sit inside the undo window), stop at `origin.kind === '

(
  messages: readonly ProjectedMessage[],
  count: number,
)

 *  undo marker (no removal). Defining the skip/stop predicate exactly once here
 *  keeps the two modes from drifting. */
function computeUndoCutoff(
  messages: readonly ProjectedMessage[],
  count: number,
): { cutoff: number; removedMessageCount: number } {
  let removedUserCount = 0;
  let removedMessageCount = 0;
  let cutoff = messages.length;
  for (let i = messages.length - 1; i >= 0; i--) {
    const origin = messages[i]?.message.origin;
    if (origin?.kind === 'injection') continue; // skip, keep
    if (origin?.kind === 'compaction_summary') break; // stop
    removedMessageCount++;
    cutoff = i;
    if (isRealUserInput(messages[i]!.message) && ++removedUserCount >= count) break;
  }
  return { cutoff, removedMessageCount };
}