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fix: streaming appended a message per chunk - track the in-flight slot

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pi streams AssistantMessages with NO id (verified against a captured
live stream and pi-ai's AssistantMessage type): the id exists only once
the server's persistTurn stamps the record. applyWireEvent minted a
FRESH c_ id per event, so message_start appended, every message_update
found no match and APPENDED another full copy, and message_end appended
again - the tail grew one message per chunk. projectView's step
separators + thinking blocks then filled the transcript with dividers
and thinking indicators mid-stream (with fresh React keys remounting
the whole subtree per chunk), cleaned up only by the settle sync's
setMessages(record).

The fix: the in-flight assistant message is tracked by SLOT -
message_start mints and remembers one client id; message_update and
message_end REPLACE that same tail entry (pi guarantees exactly one
streaming message at a time via its strict start-updates-end ordering;
the reattach replay replays the same sequence). An explicit
message.id on the wire still wins; the slot clears at message_end,
stop(), and setMessages().

Tests: all streaming fixtures rewritten to pi's real shape (no
message.id) - the old ones encoded the wrong assumption - plus a
regression pin asserting N id-less updates leave exactly ONE assistant
message in the tail with a stable slot id.

Verified live mid-stream (DOM sampled every 500ms during a teaching
turn): 0 separators throughout, thinking blocks 1-2 (one per step, not
per chunk), text growing smoothly.
This commit is contained in:
amosblomqvist
2026-09-26 02:25:04 +03:00
parent 0803fbd88d
commit 8e097752da
2 changed files with 84 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files
tests/session-core.test.ts
+65 -22
View File
@@ -68,12 +68,13 @@ function assistantMsg(id: string, text: string): LhMessage {
} as unknown as LhMessage;
}
/** A streaming assistant partial (pi events carry the FULL partial). */
function partial(id: string, blocks: unknown[], stopReason?: string): Record<string, unknown> {
/** A streaming assistant partial (pi events carry the FULL partial — and
* NO message.id: the id exists only once the server's persistTurn stamps
* the record; the client tracks the in-flight message by slot). */
function partial(blocks: unknown[], stopReason?: string): Record<string, unknown> {
return {
type: "message_update",
message: {
id,
role: "assistant",
content: blocks,
...(stopReason ? { stopReason } : {}),
@@ -205,9 +206,9 @@ describe("send (one input event, verbatim consumption)", () => {
posts.push(init.body as string);
return sseResponse(
{ type: "agent_start" },
{ type: "message_start", message: { role: "assistant", id: "a1", content: [] } },
partial("a1", [{ type: "text", text: "hello there" }]),
{ type: "message_end", message: { role: "assistant", id: "a1", content: [{ type: "text", text: "hello there" }], stopReason: "stop" } },
{ type: "message_start", message: { role: "assistant", content: [] } },
partial([{ type: "text", text: "hello there" }]),
{ type: "message_end", message: { role: "assistant", content: [{ type: "text", text: "hello there" }], stopReason: "stop" } },
{ type: "agent_end", messages: [] },
"[DONE]",
);
@@ -230,6 +231,51 @@ describe("send (one input event, verbatim consumption)", () => {
assert.equal(view.at(-1)!.parts.at(-1)!.text, "hello there");
});
it("N id-less updates replace the SAME tail slot (the per-chunk divider bug pin)", async () => {
// pi's wire (captured live, 2026-09-26): message_start/update/end carry
// AssistantMessages with NO id. The bug: minting a fresh id per event
// made every message_update APPEND a full copy — the tail grew one
// message per chunk, and projectView's step separators + thinking
// blocks made the transcript fill with dividers mid-stream (cleaned up
// only by the settle sync). The fix: the in-flight message is tracked
// by slot; updates REPLACE it.
let push: (e: unknown) => void = () => {};
const enc = new TextEncoder();
const body = new ReadableStream<Uint8Array>({
start(controller) {
push = (e) => controller.enqueue(enc.encode(e === "[DONE]" ? "data: [DONE]\n\n" : `data: ${JSON.stringify(e)}\n\n`));
},
});
globalThis.fetch = (async () => new Response(body, { status: 200 })) as typeof globalThis.fetch;
const m = model();
const done = m.send({ type: "text", text: "go" });
const settle = () => new Promise((r) => setTimeout(r, 0));
push({ type: "message_start", message: { role: "assistant", content: [{ type: "thinking", thinking: "hmm" }] } });
for (const text of ["Hel", "Hello", "Hello wor", "Hello world"]) {
push(partial([{ type: "thinking", thinking: "hmm" }, { type: "text", text }]));
await settle();
}
// MID-STREAM: exactly ONE assistant message in the tail — never one
// per chunk — carrying the LATEST partial (full snapshot, not deltas).
const assistants = m.getState().nativeMessages.filter((x) => (x as { role?: string }).role === "assistant");
assert.equal(assistants.length, 1, "one streaming message, replaced in place");
assert.equal(m.getState().messages.at(-1)!.parts.filter((p) => p.type === "text").length, 1);
assert.equal(m.getState().messages.at(-1)!.parts.at(-1)!.text, "Hello world");
// Stable id across updates → stable view-part keys (no per-chunk
// remount of the whole transcript, mermaid included).
const idMid = (assistants[0] as { id?: string }).id;
assert.match(idMid ?? "", /^c_/, "client-minted slot id");
push({ type: "message_end", message: { role: "assistant", content: [{ type: "thinking", thinking: "hmm" }, { type: "text", text: "Hello world" }], stopReason: "stop" } });
push({ type: "agent_end", messages: [] });
push("[DONE]");
await done;
const final = m.getState().nativeMessages.filter((x) => (x as { role?: string }).role === "assistant");
assert.equal(final.length, 1);
assert.equal((final[0] as { id?: string }).id, idMid, "same slot through message_end");
});
it("a 503 refusal surfaces the RAW body text (parseModelsRefusal's contract)", async () => {
globalThis.fetch = (async () =>
new Response(JSON.stringify({ code: "models_not_configured", missing: ["strong"] }), {
@@ -305,7 +351,6 @@ describe("send (one input event, verbatim consumption)", () => {
type: "message_start",
message: {
role: "assistant",
id: "a1",
content: [
{ type: "toolCall", id: "q1", name: "quiz", arguments: {} },
{ type: "toolCall", id: "bad1", name: "quiz", arguments: {} },
@@ -327,7 +372,7 @@ describe("send (one input event, verbatim consumption)", () => {
// null and crash the whole render (the live crash, 2026-09-26).
push({
type: "turn_end",
message: { role: "assistant", id: "a1", content: [{ type: "text", text: "" }], stopReason: "toolUse" },
message: { role: "assistant", content: [{ type: "text", text: "" }], stopReason: "toolUse" },
toolResults: [
{
id: "tr_q1",
@@ -352,8 +397,8 @@ describe("send (one input event, verbatim consumption)", () => {
it("a provider error rides VERBATIM (owner ruling) — no masking anywhere", async () => {
globalThis.fetch = (async () =>
sseResponse(
partial("a1", [{ type: "text", text: "" }]),
{ type: "message_end", message: { role: "assistant", id: "a1", content: [{ type: "text", text: "" }], stopReason: "error", errorMessage: "OpenRouter 429: rate limited" } },
partial([{ type: "text", text: "" }]),
{ type: "message_end", message: { role: "assistant", content: [{ type: "text", text: "" }], stopReason: "error", errorMessage: "OpenRouter 429: rate limited" } },
{ type: "agent_end", messages: [] },
"[DONE]",
)) as typeof globalThis.fetch;
@@ -374,7 +419,7 @@ describe("resumeStream (the reattach path)", () => {
urls.push(url);
if (url === "/api/chats/chat_x") return Response.json({ messages: [] });
if (url === "/api/chats/chat_x/stream")
return dripped(sse({ type: "message_start", message: { role: "assistant", id: "a1", content: [{ type: "text", text: "hi" }] } }, "[DONE]"), 8);
return dripped(sse({ type: "message_start", message: { role: "assistant", content: [{ type: "text", text: "hi" }] } }, "[DONE]"), 8);
throw new Error(`unexpected fetch: ${url}`);
}) as typeof globalThis.fetch;
const m = model();
@@ -408,8 +453,8 @@ describe("resumeStream (the reattach path)", () => {
if (url === "/api/chats/chat_x") return Response.json({ messages: [assistantMsg("seed", "the question")] });
if (url === "/api/chats/chat_x/stream")
return sseResponse(
{ type: "message_start", message: { role: "assistant", id: "run1", content: [{ type: "text", text: "the reaction" }] } },
{ type: "message_end", message: { role: "assistant", id: "run1", content: [{ type: "text", text: "the reaction" }], stopReason: "stop" } },
{ type: "message_start", message: { role: "assistant", content: [{ type: "text", text: "the reaction" }] } },
{ type: "message_end", message: { role: "assistant", content: [{ type: "text", text: "the reaction" }], stopReason: "stop" } },
{ type: "agent_end", messages: [] },
"[DONE]",
);
@@ -433,9 +478,9 @@ describe("resumeStream (the reattach path)", () => {
if (url === "/api/chats/chat_x/stream")
return dripped(
sse(
{ type: "message_start", message: { role: "assistant", id: "a1", content: [] } },
partial("a1", [{ type: "text", text: "hi" }]),
{ type: "message_end", message: { role: "assistant", id: "a1", content: [{ type: "text", text: "hi" }], stopReason: "stop" } },
{ type: "message_start", message: { role: "assistant", content: [] } },
partial([{ type: "text", text: "hi" }]),
{ type: "message_end", message: { role: "assistant", content: [{ type: "text", text: "hi" }], stopReason: "stop" } },
) + sse("[DONE]"),
1,
);
@@ -470,15 +515,13 @@ function userText(id: string, text: string): LhMessage {
describe("adoptRecord — append-only adoption", () => {
it("splices a server-added steer between the record and the live tail", () => {
const m = model({ initialMessages: [userText("u1", "topic")] });
m.applyWireEvent({ type: "message_start", message: { role: "assistant", id: "a_live", content: [{ type: "text", text: "streaming" }] } });
m.applyWireEvent({ type: "message_start", message: { role: "assistant", content: [{ type: "text", text: "streaming" }] } });
const steer = { ...newUserMessage("steered content"), id: "steer_1" } as LhMessage & { role: "user" };
const record = [userText("u1", "topic"), steer];
m.adoptRecord(record);
assert.deepEqual(
m.getState().nativeMessages.map((x) => x.id),
["u1", "steer_1", "a_live"],
"the steer shows NOW, the live tail stays last",
);
const ids = m.getState().nativeMessages.map((x) => x.id);
assert.deepEqual(ids.slice(0, 2), ["u1", "steer_1"], "the steer shows NOW");
assert.match(ids[2] ?? "", /^c_/, "the live streaming tail stays last (client slot id)");
});
it("a missing base id (record rewrite) bails — the idle full sync is the net", () => {