fix(ai): stop streams getting cut off and keep tool steps across messages

plugins/ai/src/frontend/transcript.ts

@@ -0,0 +1,82 @@
+import type { AiProposal } from "./ai-api";
+import type { StreamState, ToolActivity } from "./use-ai-stream";
+
+/** A finished part of the conversation, kept after the stream resets. */
+export type HistoryEntry =
+  | { kind: "message"; role: "user" | "assistant"; content: string }
+  | { kind: "tool"; tool: ToolActivity };
+
+/** One entry in the rendered conversation, in the order it happened. */
+export type TimelineItem =
+  | {
+      kind: "message";
+      key: string;
+      role: "user" | "assistant";
+      content: string;
+    }
+  /** live is false for a past run's step, which can never still be running. */
+  | { kind: "tool"; key: string; tool: ToolActivity; live: boolean }
+  | { kind: "proposal"; key: string; proposal: AiProposal };
+
+export function userEntry(content: string): HistoryEntry {
+  return { kind: "message", role: "user", content };
+}
+
+/**
+ * What a finished run leaves in the transcript: its tool steps, then its
+ * reply. Tool ids are only unique within one run, so they get a run prefix.
+ */
+export function finishedRunEntries(
+  runId: number,
+  tools: ToolActivity[],
+  reply: string,
+): HistoryEntry[] {
+  const entries: HistoryEntry[] = tools.map((tool) => ({
+    kind: "tool",
+    tool: { ...tool, id: `run-${runId}-${tool.id}` },
+  }));
+  if (reply)
+    entries.push({ kind: "message", role: "assistant", content: reply });
+  return entries;
+}
+
+/** Past runs, then the run in progress, then its proposals. */
+export function buildTimeline(
+  history: HistoryEntry[],
+  state: Pick<StreamState, "tools" | "assistantText">,
+  proposals: AiProposal[],
+): TimelineItem[] {
+  const timeline: TimelineItem[] = history.map((entry, index) =>
+    entry.kind === "tool"
+      ? { kind: "tool", key: entry.tool.id, tool: entry.tool, live: false }
+      : {
+          kind: "message",
+          key: `history-${index}`,
+          role: entry.role,
+          content: entry.content,
+        },
+  );
+
+  for (const tool of state.tools) {
+    timeline.push({ kind: "tool", key: tool.id, tool, live: true });
+  }
+
+  if (state.assistantText) {
+    timeline.push({
+      kind: "message",
+      key: "streaming",
+      role: "assistant",
+      content: state.assistantText,
+    });
+  }
+
+  for (const proposal of proposals) {
+    timeline.push({
+      kind: "proposal",
+      key: `proposal-${proposal.id}`,
+      proposal,
+    });
+  }
+
+  return timeline;
+}