fix(ai-chat): WYSIWYG Copy chat export keeps the on-screen partial reply (#160)

"Copy chat" built the Markdown from persisted rows plus a live tail that was
only included while isStreaming. When a turn was interrupted (dropped stream /
"Lost connection" banner) isStreaming flipped false, the live tail was dropped,
and the partial assistant reply visible on screen — whose row often never
persisted — vanished from the export, leaving only the user messages.

- buildChatMarkdown is now live-first: the on-screen `live` messages ARE the
  document. Each is matched to a persisted row by id to enrich it with token
  usage / error / timestamp; authoritative usage/error already on the live
  message win over the row. When `live` is empty it falls back to the persisted
  rows (old format preserved). Only the tail assistant is flagged "still
  generating", and only when it is genuinely the streaming tail — so the
  status==="submitted" window (tail is the user message) never mislabels the
  previous, completed answer.
- The on-screen banner (classified error / dropped connection / manual stop) is
  flattened to a string in ChatThread, mirrored into liveStateRef alongside the
  messages/isStreaming snapshot, and appended at the end of the export.
- handleCopy maps the live messages and passes live/rows/isStreaming/banner.

Tests: chat-markdown rewritten for the live/enrichment/fallback/banner paths and
the submitted-window regression (26); full ai-chat suite green (186). tsc clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/src/features/ai-chat/components/ai-chat-window.tsx

@@ -151,9 +151,14 @@ export default function AiChatWindow() {
   // Live snapshot of the active thread's useChat state, kept up to date by
   // ChatThread. Lets the export include the in-progress (not-yet-persisted)
   // streaming turn. A ref avoids re-rendering this window on every token.
-  const liveThreadRef = useRef<{ messages: UIMessage[]; isStreaming: boolean }>({
+  const liveThreadRef = useRef<{
+    messages: UIMessage[];
+    isStreaming: boolean;
+    banner: string | null;
+  }>({
     messages: [],
     isStreaming: false,
+    banner: null,
   });
 
   // Live turn-token total (reasoning + output) for the in-flight turn, pushed up
@@ -249,28 +254,42 @@ export default function AiChatWindow() {
   // call) and copy it to the clipboard. The "Copied" notification is the
   // feedback.
   const handleCopy = useCallback(() => {
+    // Export gate. Requiring at least one persisted row means a brand-new chat
+    // whose VERY FIRST turn dropped before the server persisted even the user
+    // message cannot be exported (the button is also hidden — see `canExport`).
+    // That narrow first-turn case is deliberately out of scope for #160; the user
+    // message is normally persisted before model contact, so an interrupted later
+    // turn still has rows and exports the on-screen partial reply WYSIWYG.
     if (!activeChatId || !messageRows || messageRows.length === 0) return;
-    // While the active thread is streaming, the current user message and the
+    // WYSIWYG export: the live on-screen messages ARE the document (so a partial
-    // in-progress assistant reply are NOT yet in messageRows (the persisted
+    // reply from an interrupted turn — which never reached the persisted rows —
-    // query is only refetched after the turn finishes). Pull the live tail —
+    // is exported just as it appears). The persisted rows enrich each live
-    // messages whose id is not among the persisted rows — and append them,
+    // message (token usage / error / timestamp) by id and serve as the fallback
-    // flagging the streaming assistant message as still generating.
+    // when the live mirror is empty. The on-screen banner is appended too. See
+    // issue #160.
     const live = liveThreadRef.current;
-    const rowIds = new Set(messageRows.map((r) => r.id));
-    const pending = live.isStreaming
-      ? live.messages
-          .filter((m) => !rowIds.has(m.id))
-          .map((m) => ({
-            role: m.role,
-            parts: (m.parts ?? []) as { type: string; text?: string }[],
-            generating: m.role === "assistant",
-          }))
-      : [];
     const markdown = buildChatMarkdown({
       title: activeChat?.title ?? null,
       chatId: activeChatId,
+      live: live.messages.map((m) => ({
+        id: m.id,
+        role: m.role,
+        parts: (m.parts ?? []) as { type: string; text?: string }[],
+        metadata: m.metadata as
+          | {
+              usage?: {
+                inputTokens?: number;
+                outputTokens?: number;
+                totalTokens?: number;
+                reasoningTokens?: number;
+              };
+              error?: string;
+            }
+          | undefined,
+      })),
       rows: messageRows,
-      pending,
+      isStreaming: live.isStreaming,
+      banner: live.banner,
       t,
     });
     clipboard.copy(markdown);

apps/client/src/features/ai-chat/components/chat-thread.tsx

@@ -73,7 +73,11 @@ interface ChatThreadProps {
    *  "Copy chat" export can include the in-progress, not-yet-persisted
    *  assistant message. A ref (not state) avoids re-rendering the parent on
    *  every streamed delta. */
-  liveStateRef?: MutableRefObject<{ messages: UIMessage[]; isStreaming: boolean }>;
+  liveStateRef?: MutableRefObject<{
+    messages: UIMessage[];
+    isStreaming: boolean;
+    banner: string | null;
+  }>;
   /** Reports the live turn-token total (reasoning + output) for the in-flight
    *  turn so the parent can show a header badge that ticks mid-stream. THROTTLED
    *  here (~8 Hz) so the parent re-renders a handful of times a second, not on
@@ -309,18 +313,37 @@ export default function ChatThread({
     if (isStreaming) setStopNotice(null);
   }, [isStreaming]);
 
+  // Classify the turn error into a heading + detail so the banner names the cause
+  // (connection reset, timeout, rate limit, context overflow, quota, ...) instead
+  // of a generic "Something went wrong". Computed here (not only in the JSX) so
+  // the SAME on-screen banner text can be mirrored into the export (issue #160).
+  const errorView = error ? describeChatError(error.message ?? "", t) : null;
+
+  // The exact banner the user sees under the message list, flattened to a single
+  // string for the "Copy chat" export so the artifact records the interruption
+  // WYSIWYG. Mirrors the JSX precedence below: error first, else the stop notice.
+  const banner = errorView
+    ? errorView.detail
+      ? `${errorView.title} — ${errorView.detail}`
+      : errorView.title
+    : stopNotice === "manual"
+      ? t("Response stopped.")
+      : stopNotice === "disconnect"
+        ? t("Connection lost — the answer was interrupted.")
+        : null;
+
   // Mirror the live useChat snapshot into the parent-owned ref so the export
-  // (handled in AiChatWindow) can include the in-progress streaming turn. The
+  // (handled in AiChatWindow) can include the in-progress streaming turn AND the
-  // cleanup clears the ref on unmount so a thread torn down by `key` on chat
+  // on-screen banner. The cleanup clears the ref on unmount so a thread torn down
-  // switch can't leak its (possibly still-streaming) tail into the next chat's
+  // by `key` on chat switch can't leak its (possibly still-streaming) tail into
-  // export before the new thread's effect repopulates the ref.
+  // the next chat's export before the new thread's effect repopulates the ref.
   useEffect(() => {
     if (!liveStateRef) return;
-    liveStateRef.current = { messages, isStreaming };
+    liveStateRef.current = { messages, isStreaming, banner };
     return () => {
-      liveStateRef.current = { messages: [], isStreaming: false };
+      liveStateRef.current = { messages: [], isStreaming: false, banner: null };
     };
-  }, [liveStateRef, messages, isStreaming]);
+  }, [liveStateRef, messages, isStreaming, banner]);
 
   // Report the live turn-token total to the parent header badge, THROTTLED to
   // ~8 Hz so the parent re-renders a few times a second instead of on every
@@ -370,11 +393,6 @@ export default function ChatThread({
     };
   }, []);
 
-  // Classify the turn error into a heading + detail so the banner names the cause
-  // (connection reset, timeout, rate limit, context overflow, quota, ...) instead
-  // of a generic "Something went wrong".
-  const errorView = error ? describeChatError(error.message ?? "", t) : null;
-
   // A role was picked with autoStart=false: the role is bound but NOTHING was
   // sent, so chatId stays null and the empty state would keep showing the cards.
   // This flag hides the cards and reveals the composer (with the role indicated)

apps/client/src/features/ai-chat/utils/chat-markdown.test.ts

@@ -367,125 +367,258 @@ describe("buildChatMarkdown — token totals", () => {
   });
 });
 
-describe("buildChatMarkdown — pending / in-progress messages", () => {
+// A minimal on-screen (live) message, matching the subset buildChatMarkdown reads.
-  it("continues the heading numbering after the persisted rows", () => {
+function live(partial: {
+  id?: string;
+  role?: string;
+  parts?: { type: string; text?: string }[];
+  metadata?: { usage?: Record<string, number>; error?: string };
+}) {
+  return {
+    id: partial.id ?? "live-id",
+    role: partial.role ?? "assistant",
+    parts: partial.parts ?? [],
+    metadata: partial.metadata,
+  };
+}
+
+describe("buildChatMarkdown — live (WYSIWYG) source", () => {
+  it("uses the live messages as the document (what's on screen), numbered from 1", () => {
     const md = buildChatMarkdown({
       title: "t",
       chatId: "c",
-      rows: [row({ role: "user", content: "persisted" })],
+      // Persisted rows hold only the user turn; the assistant reply is live-only.
-      pending: [
+      rows: [row({ id: "u1", role: "user", content: "persisted user" })],
-        {
+      live: [
-          role: "user",
+        live({ id: "u1", role: "user", parts: [{ type: "text", text: "on-screen user" }] }),
-          parts: [{ type: "text", text: "live question" }],
+        live({ id: "a1", role: "assistant", parts: [{ type: "text", text: "on-screen reply" }] }),
-          generating: false,
-        },
-        {
-          role: "assistant",
-          parts: [{ type: "text", text: "live answer" }],
-          generating: true,
-        },
       ],
+      isStreaming: false,
       t,
     });
     expect(md).toContain("## 1. You");
-    expect(md).toContain("## 2. You");
+    expect(md).toContain("## 2. AI agent");
-    expect(md).toContain("## 3. AI agent");
+    expect(md).toContain("on-screen user");
-    expect(md).toContain("live question");
+    expect(md).toContain("on-screen reply");
-    expect(md).toContain("live answer");
+    // Message count reflects the LIVE document, not rows + live.
+    expect(md).toContain("- Messages: 2");
   });
 
-  it("flags a generating assistant pending message as still being generated", () => {
+  it("captures a partial reply from an interrupted (non-streaming) turn — no 'generating' note", () => {
     const md = buildChatMarkdown({
       title: "t",
       chatId: "c",
-      rows: [row({ role: "user", content: "persisted" })],
+      rows: [row({ id: "u1", role: "user", content: "q" })],
-      pending: [
+      live: [
-        {
+        live({ id: "u1", role: "user", parts: [{ type: "text", text: "q" }] }),
+        live({
+          id: "a-live",
           role: "assistant",
-          parts: [{ type: "text", text: "partial reply" }],
+          parts: [{ type: "text", text: "partial plan before the drop" }],
-          generating: true,
+        }),
-        },
       ],
+      isStreaming: false, // the stream dropped — not streaming anymore
+      banner: "Connection lost — the answer was interrupted.",
       t,
     });
-    expect(md).toContain("partial reply");
+    // The partial assistant answer that was on screen IS in the export.
-    expect(md).toContain("still being generated");
+    expect(md).toContain("partial plan before the drop");
+    // It is NOT flagged still-generating (the turn is over, just interrupted).
+    expect(md).not.toContain("still being generated");
+    // The on-screen banner is recorded at the end.
+    expect(md).toContain("Connection lost — the answer was interrupted.");
   });
 
-  it("renders a non-generating user pending message without the note", () => {
+  it("flags ONLY the tail assistant as still generating, and only while streaming", () => {
+    const streaming = buildChatMarkdown({
+      title: "t",
+      chatId: "c",
+      rows: [],
+      live: [
+        live({ id: "a", role: "assistant", parts: [{ type: "text", text: "done earlier" }] }),
+        live({ id: "u", role: "user", parts: [{ type: "text", text: "next q" }] }),
+        live({ id: "b", role: "assistant", parts: [{ type: "text", text: "streaming now" }] }),
+      ],
+      isStreaming: true,
+      t,
+    });
+    // Exactly one "still being generated" note (the tail assistant).
+    expect(streaming.match(/still being generated/g)?.length).toBe(1);
+
+    const idle = buildChatMarkdown({
+      title: "t",
+      chatId: "c",
+      rows: [],
+      live: [live({ id: "b", role: "assistant", parts: [{ type: "text", text: "final" }] })],
+      isStreaming: false,
+      t,
+    });
+    expect(idle).not.toContain("still being generated");
+  });
+
+  it("does NOT flag a completed assistant as generating when the streaming tail is a user message", () => {
+    // The `status === "submitted"` window: the user just sent, isStreaming is
+    // already true, but the new assistant turn has no message yet so the tail is
+    // the USER message. The previous assistant answer is complete on screen and
+    // must not be marked still-generating (WYSIWYG; regression for #160 review).
     const md = buildChatMarkdown({
       title: "t",
       chatId: "c",
-      rows: [row({ role: "user", content: "persisted" })],
+      rows: [],
-      pending: [
+      live: [
-        {
+        live({ id: "a", role: "assistant", parts: [{ type: "text", text: "completed answer" }] }),
-          role: "user",
+        live({ id: "u", role: "user", parts: [{ type: "text", text: "the new question" }] }),
-          parts: [{ type: "text", text: "my live message" }],
-          generating: false,
-        },
       ],
+      isStreaming: true,
       t,
     });
-    expect(md).toContain("my live message");
+    expect(md).toContain("completed answer");
     expect(md).not.toContain("still being generated");
   });
 
-  it("includes the pending messages in the metadata message count", () => {
+  it("emits the heading + note for a streaming tail assistant with empty parts", () => {
     const md = buildChatMarkdown({
       title: "t",
       chatId: "c",
-      rows: [
+      rows: [row({ id: "u1", role: "user", content: "q" })],
-        row({ role: "user", content: "a" }),
+      live: [
-        row({ role: "assistant", content: "b" }),
+        live({ id: "u1", role: "user", parts: [{ type: "text", text: "q" }] }),
-      ],
+        live({ id: "a-live", role: "assistant", parts: [] }),
-      pending: [
-        {
-          role: "user",
-          parts: [{ type: "text", text: "c" }],
-          generating: false,
-        },
-        {
-          role: "assistant",
-          parts: [{ type: "text", text: "d" }],
-          generating: true,
-        },
-      ],
-      t,
-    });
-    // 2 persisted rows + 2 pending = 4.
-    expect(md).toContain("- Messages: 4");
-  });
-
-  it("emits the heading and note for a generating assistant with empty parts", () => {
-    expect(() =>
-      buildChatMarkdown({
-        title: "t",
-        chatId: "c",
-        rows: [row({ role: "user", content: "persisted" })],
-        pending: [
-          {
-            role: "assistant",
-            parts: [],
-            generating: true,
-          },
-        ],
-        t,
-      }),
-    ).not.toThrow();
-    const md = buildChatMarkdown({
-      title: "t",
-      chatId: "c",
-      rows: [row({ role: "user", content: "persisted" })],
-      pending: [
-        {
-          role: "assistant",
-          parts: [],
-          generating: true,
-        },
       ],
+      isStreaming: true,
       t,
     });
     expect(md).toContain("## 2. AI agent");
     expect(md).toContain("still being generated");
   });
 });
+
+describe("buildChatMarkdown — live enrichment from persisted rows", () => {
+  it("pulls usage / error / timestamp from the persisted row matched by id", () => {
+    const md = buildChatMarkdown({
+      title: "t",
+      chatId: "c",
+      rows: [
+        row({
+          id: "a1",
+          role: "assistant",
+          content: "x",
+          createdAt: "2026-06-22T10:00:00.000Z",
+          metadata: { usage: { inputTokens: 10, outputTokens: 5 }, error: "rate limited" },
+        }),
+      ],
+      live: [
+        // Same id as the persisted row, but no usage/error/timestamp on the live msg.
+        live({ id: "a1", role: "assistant", parts: [{ type: "text", text: "reply" }] }),
+      ],
+      isStreaming: false,
+      t,
+    });
+    expect(md).toContain("reply");
+    // Token footer + total come from the enriched row.
+    expect(md).toContain("_Tokens — in: 10, out: 5, total: 15_");
+    expect(md).toContain("- Total tokens: 15");
+    expect(md).toContain("**⚠️ Error:** rate limited");
+    // The persisted timestamp is carried into the export.
+    expect(md).toContain("<!-- 2026-06-22T10:00:00.000Z -->");
+  });
+
+  it("prefers authoritative usage already on the live message over the row's", () => {
+    const md = buildChatMarkdown({
+      title: "t",
+      chatId: "c",
+      rows: [
+        row({
+          id: "a1",
+          role: "assistant",
+          content: "x",
+          metadata: { usage: { inputTokens: 1, outputTokens: 1, totalTokens: 2 } },
+        }),
+      ],
+      live: [
+        live({
+          id: "a1",
+          role: "assistant",
+          parts: [{ type: "text", text: "reply" }],
+          metadata: { usage: { inputTokens: 100, outputTokens: 50, totalTokens: 150 } },
+        }),
+      ],
+      isStreaming: false,
+      t,
+    });
+    // The live (authoritative, freshest) usage wins, not the stale row usage.
+    expect(md).toContain("- Total tokens: 150");
+    expect(md).not.toContain("- Total tokens: 2");
+  });
+
+  it("a current-turn live message with no matching row renders without a footer", () => {
+    const md = buildChatMarkdown({
+      title: "t",
+      chatId: "c",
+      rows: [row({ id: "u1", role: "user", content: "q" })],
+      live: [
+        live({ id: "u1", role: "user", parts: [{ type: "text", text: "q" }] }),
+        live({ id: "a-live", role: "assistant", parts: [{ type: "text", text: "fresh reply" }] }),
+      ],
+      isStreaming: false,
+      t,
+    });
+    expect(md).toContain("fresh reply");
+    // No persisted row for the live assistant -> no token footer, no timestamp.
+    expect(md).not.toContain("_Tokens —");
+    expect(md).not.toContain("<!-- undefined -->");
+  });
+});
+
+describe("buildChatMarkdown — fallback + banner", () => {
+  it("falls back to the persisted rows when there are no live messages", () => {
+    const md = buildChatMarkdown({
+      title: "t",
+      chatId: "c",
+      rows: [
+        row({ role: "user", content: "from rows" }),
+        row({
+          role: "assistant",
+          content: "answer",
+          metadata: { usage: { inputTokens: 4, outputTokens: 6 } },
+        }),
+      ],
+      live: [], // empty live mirror -> fallback path
+      isStreaming: false,
+      t,
+    });
+    expect(md).toContain("## 1. You");
+    expect(md).toContain("## 2. AI agent");
+    expect(md).toContain("from rows");
+    expect(md).toContain("- Messages: 2");
+    expect(md).toContain("- Total tokens: 10");
+  });
+
+  it("appends the on-screen banner once, after the messages", () => {
+    const md = buildChatMarkdown({
+      title: "t",
+      chatId: "c",
+      rows: [row({ role: "user", content: "q" })],
+      live: [live({ id: "u", role: "user", parts: [{ type: "text", text: "q" }] })],
+      isStreaming: false,
+      banner: "Rate limit reached — try again shortly.",
+      t,
+    });
+    expect(md).toContain("_⚠️ Rate limit reached — try again shortly._");
+    // Banner comes after the (only) message block.
+    expect(md.indexOf("Rate limit reached")).toBeGreaterThan(md.indexOf("## 1."));
+  });
+
+  it("omits the banner block when there is no banner", () => {
+    const md = buildChatMarkdown({
+      title: "t",
+      chatId: "c",
+      rows: [row({ role: "user", content: "q" })],
+      live: [live({ id: "u", role: "user", parts: [{ type: "text", text: "q" }] })],
+      isStreaming: false,
+      banner: null,
+      t,
+    });
+    expect(md).not.toContain("_⚠️");
+  });
+});

apps/client/src/features/ai-chat/utils/chat-markdown.ts

@@ -25,11 +25,23 @@ type Translate = (key: string, values?: Record<string, unknown>) => string;
 interface BuildChatMarkdownArgs {
   title: string | null;
   chatId: string;
+  /** The live, on-screen messages — the WYSIWYG source of the export. When
+   *  present and non-empty these DRIVE the document (so it mirrors exactly what
+   *  the user sees, including a partial reply from an interrupted turn). Each is
+   *  matched to a persisted row by `id` to enrich it with token usage / error /
+   *  timestamp. When absent or empty the builder falls back to `rows`. */
+  live?: LiveMessage[];
+  /** Persisted message rows. Enrichment source (matched to `live` by id) AND the
+   *  fallback document source when `live` is empty. */
   rows: IAiChatMessageRow[];
-  /** In-progress, not-yet-persisted live messages (the current streaming
+  /** Whether the live thread is still streaming. Only then is the tail assistant
-   *  turn) to append after the persisted rows. `generating: true` adds a
+   *  message flagged "still generating"; an interrupted (non-streaming) partial
-   *  note that the message is still being produced. */
+   *  reply is exported as-is and the `banner` explains the interruption. */
-  pending?: PendingMessage[];
+  isStreaming?: boolean;
+  /** The on-screen banner text (error / dropped connection / manual stop),
+   *  appended at the end of the export so the artifact records the interruption
+   *  the user saw. */
+  banner?: string | null;
   t: Translate;
 }
 
@@ -39,10 +51,31 @@ interface TextLikePart {
   text?: string;
 }
 
-/** A live, not-yet-persisted message (current streaming turn) to append. */
+/** Authoritative per-turn usage the server attaches to a message / row. */
-interface PendingMessage {
+interface UsageLike {
+  inputTokens?: number;
+  outputTokens?: number;
+  totalTokens?: number;
+  reasoningTokens?: number;
+}
+
+/** A live, on-screen message (subset of the AI SDK UIMessage we consume). */
+interface LiveMessage {
+  id: string;
   role: "user" | "assistant" | string;
   parts: TextLikePart[];
+  metadata?: { usage?: UsageLike; error?: string };
+}
+
+/** One message normalized for rendering, regardless of live/persisted origin. */
+interface ExportItem {
+  role: string;
+  parts: TextLikePart[];
+  usage?: UsageLike;
+  error?: string;
+  /** ISO timestamp from the persisted row, when one is known. */
+  createdAt?: string;
+  /** True only for the tail assistant message while the thread is streaming. */
   generating: boolean;
 }
 
@@ -127,53 +160,128 @@ function renderMessageParts(parts: TextLikePart[], t: Translate): string[] {
   return out;
 }
 
+/** Resolve a persisted row's parts: prefer the rich persisted parts, else a
+ *  single text part built from the plain-text content (mirrors `rowToUiMessage`). */
+function rowParts(row: IAiChatMessageRow): TextLikePart[] {
+  return Array.isArray(row.metadata?.parts) && row.metadata.parts.length > 0
+    ? (row.metadata.parts as TextLikePart[])
+    : [{ type: "text", text: row.content ?? "" }];
+}
+
+/**
+ * Normalize the export to one ordered list of {@link ExportItem}, WYSIWYG-first:
+ *
+ * - When `live` messages are present, THEY are the document (what the user sees,
+ *   incl. an interrupted turn's partial reply). Each is matched to a persisted
+ *   row by `id` to pull token usage / error / timestamp — a live message of the
+ *   CURRENT turn has no matching row yet, so it simply renders without a footer.
+ *   Authoritative `usage`/`error` already on the live message metadata win over
+ *   the row (the server attaches usage to the streamed message at a step
+ *   boundary before the row is refetched). Only the tail assistant message is
+ *   flagged `generating`, and only while `isStreaming`.
+ * - When `live` is empty (e.g. the export runs before the live mirror is
+ *   populated), fall back to the persisted `rows` so the format never regresses.
+ */
+function resolveItems(
+  live: LiveMessage[] | undefined,
+  rows: IAiChatMessageRow[],
+  isStreaming: boolean,
+): ExportItem[] {
+  if (live && live.length > 0) {
+    const rowsById = new Map(rows.map((r) => [r.id, r]));
+    // The "still generating" note may apply ONLY to an assistant message that is
+    // the actual TAIL of the list — that is where the on-screen typing indicator
+    // sits. While `status === "submitted"` (isStreaming true) right after the
+    // user hit send, the tail is the USER message and the new assistant turn has
+    // no message yet; the previous assistant answer is shown complete on screen,
+    // so it must NOT be flagged (the indicator renders as a separate bottom
+    // block, not on that answer).
+    const lastIndex = live.length - 1;
+    const tailIsStreamingAssistant =
+      isStreaming && live[lastIndex]?.role === "assistant";
+    return live.map((m, i) => {
+      const row = rowsById.get(m.id);
+      return {
+        role: m.role,
+        parts: m.parts ?? [],
+        // Authoritative usage/error already on the live message (the server
+        // attaches usage to the streamed message at a step boundary) wins over
+        // the persisted row; a current-turn live message has no matching row yet
+        // and simply renders without a token footer (the accepted WYSIWYG
+        // tradeoff — an interrupted turn loses only its token footer, not text).
+        usage: m.metadata?.usage ?? row?.metadata?.usage,
+        error: m.metadata?.error ?? row?.metadata?.error ?? undefined,
+        createdAt: row?.createdAt,
+        generating: tailIsStreamingAssistant && i === lastIndex,
+      };
+    });
+  }
+
+  return rows.map((row) => ({
+    role: row.role,
+    parts: rowParts(row),
+    usage: row.metadata?.usage,
+    error: row.metadata?.error ?? undefined,
+    createdAt: row.createdAt,
+    generating: false,
+  }));
+}
+
 /**
  * Serialize a chat to a Markdown string. Pure (apart from `new Date()` for the
  * export timestamp), so it is straightforward to unit-test.
  */
 export function buildChatMarkdown(args: BuildChatMarkdownArgs): string {
-  const { title, chatId, rows, pending, t } = args;
+  const { title, chatId, live, rows, isStreaming, banner, t } = args;
   const blocks: string[] = [];
 
+  const items = resolveItems(live, rows, isStreaming === true);
+
   const heading = (title ?? "").trim() || t("Untitled chat");
   blocks.push(`# ${heading}`);
 
   // Metadata bullet list. Total tokens is only shown when there is a sum.
-  const totalTokens = rows.reduce((sum, row) => {
+  const totalTokens = items.reduce(
-    const usage = row.metadata?.usage;
+    (sum, item) => (item.usage ? sum + rowTokens(item.usage) : sum),
-    return usage ? sum + rowTokens(usage) : sum;
+    0,
-  }, 0);
+  );
   const meta = [
     `- Chat ID: \`${chatId}\``,
     `- Exported: ${new Date().toISOString()}`,
-    `- Messages: ${rows.length + (pending?.length ?? 0)}`,
+    `- Messages: ${items.length}`,
   ];
   if (totalTokens > 0) meta.push(`- Total tokens: ${totalTokens}`);
   blocks.push(meta.join("\n"));
 
-  rows.forEach((row, index) => {
+  items.forEach((item, index) => {
     blocks.push("---");
 
-    const roleLabel = row.role === "assistant" ? t("AI agent") : t("You");
+    const roleLabel = item.role === "assistant" ? t("AI agent") : t("You");
     blocks.push(`## ${index + 1}. ${roleLabel}`);
 
     // Created-at kept in source as an HTML comment (out of the rendered prose).
-    blocks.push(`<!-- ${row.createdAt} -->`);
+    // A live message of the current turn has no persisted row yet — omit it.
+    if (item.createdAt) blocks.push(`<!-- ${item.createdAt} -->`);
 
-    // Resolve parts: prefer the rich persisted parts, else a single text part
+    blocks.push(...renderMessageParts(item.parts, t));
-    // built from the plain-text content (mirrors `rowToUiMessage`).
-    const parts: TextLikePart[] =
-      Array.isArray(row.metadata?.parts) && row.metadata.parts.length > 0
-        ? (row.metadata.parts as TextLikePart[])
-        : [{ type: "text", text: row.content ?? "" }];
 
-    blocks.push(...renderMessageParts(parts, t));
+    // A generating assistant may have empty/no parts yet — the heading (above)
-
+    // and this note still record the in-progress turn.
-    if (row.metadata?.error) {
+    if (item.generating) {
-      blocks.push(`**⚠️ Error:** ${row.metadata.error}`);
+      blocks.push(
+        "_⏳ This message is still being generated — the export captured a partial, in-progress response._",
+      );
     }
 
-    const usage = row.metadata?.usage;
+    // A persisted per-message error (the raw provider text) may coexist with the
+    // trailing `banner` (the classified on-screen alert) when the failed turn's
+    // row has already been refetched by export time. They describe the same
+    // failure at different fidelity; showing both is an accepted, minor redundancy.
+    if (item.error) {
+      blocks.push(`**⚠️ Error:** ${item.error}`);
+    }
+
+    const usage = item.usage;
     if (usage) {
       const total = usage.totalTokens ?? rowTokens(usage);
       // Reasoning (thinking) tokens are shown only when the provider reported a
@@ -188,27 +296,12 @@ export function buildChatMarkdown(args: BuildChatMarkdownArgs): string {
     }
   });
 
-  // Append the in-progress, not-yet-persisted live messages (the current
+  // Record the on-screen banner (error / dropped connection / manual stop) so
-  // streaming turn) after the persisted rows. Heading numbering CONTINUES from
+  // the export reflects exactly what the user saw, including an interruption.
-  // the persisted rows. A `generating` assistant gets a note that the captured
+  if (banner && banner.trim().length > 0) {
-  // response is partial; pending messages carry no usage/token footer yet.
-  (pending ?? []).forEach((message, p) => {
     blocks.push("---");
-
+    blocks.push(`_⚠️ ${banner.trim()}_`);
-    const num = rows.length + p + 1;
-    const roleLabel = message.role === "assistant" ? t("AI agent") : t("You");
-    blocks.push(`## ${num}. ${roleLabel}`);
-
-    blocks.push(...renderMessageParts(message.parts, t));
-
-    // A generating assistant may have empty/no parts yet — still emit the
-    // heading (above) and this note so the export shows the in-progress turn.
-    if (message.generating === true) {
-      blocks.push(
-        "_⏳ This message is still being generated — the export captured a partial, in-progress response._",
-      );
   }
-  });
 
   // Blank line between blocks so the Markdown renders cleanly.
   return blocks.join("\n\n");