1/**

2 * Fork seed construction over an exact source-event prefix.

3 * @module @deepseek-ai/dsh-session/fork

4 */

5

6import { openTurnClosers } from './repair.ts'

7import { SessionSeq } from './types.ts'

8import type { SessionEvent, SessionSeq as SessionSeqType } from './types.ts'

9

10/**

11 * Copy an inclusive event prefix, mark its inherited cut, and close its open tail with forked results

12 * and step/turn endings. Closed steps and turns are preserved unchanged.

13 * The caller validates that the boundary is an existing contiguous event seq;

14 * Session construction snapshots the borrowed events before publication.

15 *

16 * @param events - source log with contiguous seqs from zero.

17 * @param boundary - inclusive source event seq the child inherits through.

18 * @returns a new array retaining the source event objects, followed by synthetic

19 * closers outside the inherited prefix counted by `inheritedEventCount`.

20 */

21export function buildForkSeed(events: readonly SessionEvent[], boundary: SessionSeqType): SessionEvent[] {

22 const prefix = events.slice(0, boundary + 1)

23 prefix.push({

24 type: 'session/end-seed', seq: SessionSeq(boundary + 1),

25 // oxlint-disable-next-line typescript/no-non-null-assertion -- the caller validated this exact source event.

26 time: events[boundary]!.time,

27 data: { inherited: true },

28 })

29 return prefix.concat(openTurnClosers(prefix, { kind: 'forked' }))

30}