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fix(client): floor the fork anchor to a real event seq

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The fork button on a stopped assistant message was inert. Frozen
interrupted nodes carry a flow-ordering seq of turnEnd.seq - 0.9, and
session.fork takes a non-negative integer on the wire, so every such
request was rejected as invalid-params before reaching the host — where
an aborted turn's logged turn/end has always made it forkable.

SessionsService.fork floors atSeq at the wire boundary. Flooring stays
inside the anchor's own turn (every turn opens with turn/start), so the
host's first-turn/end-at-or-after cut still closes on that turn.
This commit is contained in:
ZiyaZhang
2026-07-31 05:41:45 -07:00
parent 5c4b701afe
commit 344ad0d6fb
6 changed files with 119 additions and 5 deletions
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29
packages/host/apiproxy/tests/api-proxy-fork.spec.ts
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@@ -46,7 +46,10 @@ async function composed(): Promise<Context> {
return ctx
}
function liveAgent(ctx: Context, id: string, turns: number, openTail = false): Session {
/** Tail turn appended after the completed ones: left open, or closed as aborted (a stopped turn). */
type Tail = 'none' | 'open' | 'aborted'
function liveAgent(ctx: Context, id: string, turns: number, tail: Tail = 'none'): Session {
const session = ctx.sessions.create(sid(id), { meta: { cwd: '/proj' } })
for (let turn = 1; turn <= turns; turn++) {
session.append('turn/start', { turn, trigger: { kind: 'message', source: { kind: 'user' } } })
@@ -56,12 +59,13 @@ function liveAgent(ctx: Context, id: string, turns: number, openTail = false): S
}), { surfaceOp: 'append' })
session.append('turn/end', { turn, reason: { kind: 'completed' } })
}
if (openTail) {
if (tail !== 'none') {
session.append('turn/start', { turn: turns + 1, trigger: { kind: 'message', source: { kind: 'user' } } })
session.append('user/message', createUserMessage({
content: [{ type: 'text', text: 'open prompt' }],
source: { kind: 'user' },
}), { surfaceOp: 'append' })
if (tail === 'aborted') session.append('turn/end', { turn: turns + 1, reason: { kind: 'aborted' } })
}
ctx.agents.register({ id: session.id, session, status: 'idle', ctx } as Agent)
return session
@@ -92,7 +96,7 @@ describe('sessions.fork', () => {
it('uses the last completed turn only for omitted and past-end anchors', async () => {
const ctx = await composed()
const source = liveAgent(ctx, 'session-tail', 2, true)
const source = liveAgent(ctx, 'session-tail', 2, 'open')
const proxy = api(ctx)
const expectedTypes = [
'turn/start', 'user/message', 'turn/end',
@@ -114,9 +118,26 @@ describe('sessions.fork', () => {
await ctx.fiber.dispose()
})
it('cuts through an aborted turn: stopped is closed, not open', async () => {
const ctx = await composed()
const source = liveAgent(ctx, 'session-aborted', 1, 'aborted')
// What a stopped message's fork button anchors on: the frozen node sits
// one event before its turn/end, floored client-side to that event's seq.
const anchor = (source.events.at(-1)?.seq ?? 0) - 1
const response = await api(ctx).sessions.fork(request({ sessionId: source.id, atSeq: anchor }))
expect(response.result.ok).toBe(true)
if (!response.result.ok) return
expect(ctx.sessions.get(response.result.value.sessionId)?.events.map(event => event.type)).toEqual([
'turn/start', 'user/message', 'turn/end',
'turn/start', 'user/message', 'turn/end',
'session/end-seed',
])
await ctx.fiber.dispose()
})
it('rejects an in-log anchor whose turn is still open', async () => {
const ctx = await composed()
const source = liveAgent(ctx, 'session-open', 1, true)
const source = liveAgent(ctx, 'session-open', 1, 'open')
const anchor = source.events.at(-1)?.seq ?? 0
const response = await api(ctx).sessions.fork(request({ sessionId: source.id, atSeq: anchor }))
expect(response.result).toMatchObject({