Session view shape

SessionView is the renderer-facing state accumulated by fold. It contains content, toolCalls, queuedInputs, compactions, and statusEvents. The fold returns a new view rather than mutating the previous one, so a UI can replace one state snapshot in its framework store.

import {
  emptySessionView,
  fold,
  type FoldInput,
  type SessionView,
} from "@looprig/client";

let view: SessionView = emptySessionView();
const input: FoldInput = { segment: "history", event };
const result = fold(view, input);

if (result.ok) view = result.view;

Text, thinking, and streamed tool-use chunks are represented as tagged content entries. Tool execution starts and completions merge by toolExecutionId, including when completion arrives first. Durable envelopes become status markers with their journalSeq, making cold and live output structurally comparable.

Fold history and live

Wrap a journal item as { segment: "history", event } and a parsed live frame as { segment: "live", frame }. The same fold function handles both. Heartbeats leave the view unchanged. A malformed SSE frame becomes a non-throwing FoldError result with reason upstream_frame_error; unknown delta shapes are also reported instead of silently disappearing.

for (const event of page.events) {
  const result = fold(view, { segment: "history", event });
  if (result.ok) view = result.view;
}

for await (const frame of parseSseStream(response.body)) {
  const result = fold(view, { segment: "live", frame });
  if (result.ok) view = result.view;
  else logFoldError(result.error);
}

The Events and live streams page covers frame parsing. Reconnect and exact joins explains how joinSessionView orders the two segments before folding them.

Source

The immutable SessionView model, tagged content entries, tool-call merge rules, durable markers, and fold function are in sdk/core/src/fold.ts. The fold behavior and error cases are covered in sdk/core/test/fold.test.ts.

Proof

The focused tests prove that history and live enduring frames produce the same marker shape, tool calls pair without duplicate cards, heartbeats do not change state, and bad inputs produce typed non-silent results. Use SessionView as the adapter boundary.