fix(markdown): preserve complete assistant messages on native

docs/agent-stream-performance.md

@@ -29,7 +29,7 @@ So arrival sets a _target_ and the reveal rate is derived from the backlog inste
 - **The coalescer is leading + trailing.** The first delta after an idle window flushes synchronously; only the rest of the burst waits for the trailing timer. Reverting to trailing-only adds a full window to the first character of every turn. Same shape and the same reason as `TerminalOutputCoalescer`.
 - **The leading flush adds a canonical row, and that is fine.** A burst's first chunk lands as its own timeline row. `mergeAssistantChunks` / `mergeReasoningChunks` in `timeline-projection.ts` join contiguous same-turn rows, and clients read the projected timeline, so history is unaffected. Tests that assert on raw rows have to account for the extra row; tests that assert on what a client sees do not.
 - **The store holds the full text; only the rendered slice is paced.** Copy, selection, the chat outline, and scroll geometry all read the same string the user can see. Pacing the store instead would leave the bottom anchor chasing a content height that is ahead of the reveal.
-- **One source assistant message is one display row.** Presentation projects plugin output and caches unchanged history. The shared [Markdown renderer](markdown-renderer.md) owns rendering on every platform. Chat paces the visible source and applies its 32,000-character render cap; it does not split Markdown or promote completed blocks into history.
+- **One source assistant message is one display row.** Presentation projects plugin output and caches unchanged history. The shared [Markdown renderer](markdown-renderer.md) owns rendering on every platform. Chat paces the visible source and applies a 32,000-character render cap on web; native keeps the complete message. It does not split Markdown or promote completed blocks into history.
 - **Message identity survives completion.** Assistant row ids are source message ids. Plugin rows can replace a source, so find, scroll-to-message and history reveal still use `getStreamItemMessageId`. Width-specific measurements describe whole rendered messages.
 - **First sight of a text is revealed whole.** Only growth is paced. This is what makes history hydration, timeline replay, a virtualized row remounting on scroll, and an already-finished message all render complete on first paint without a special case for each.
 - **Leaving `phase: "streaming"` snaps the reveal.** A completed turn must never be left holding characters. `layoutStream` sets the phase, so anything outside the live head with an active turn is already complete.

docs/markdown-renderer.md

@@ -2,7 +2,7 @@
 
 Use `MarkdownRenderer` for chat replies, file previews, plans, pull requests and changelog content. It uses `react-native-enriched-markdown` on iOS, Android and web. Keep source adaptation and renderer configuration in `components/markdown`; consumers supply Markdown and, when needed, its file location.
 
-Native selection belongs to the library's text view. Keep an assistant message in one row so selection can cross paragraphs, headings and lists. Code blocks and tables use the library's native views and their selection behavior. Web uses browser selection over semantic HTML. Once its WASM parser is initialized, the library parses synchronously for the first commit of each mounted row; an empty interim row would corrupt virtualized measurements and move the reader. Chat still owns paced reveal, its render cap, message identity and list measurement; it does not choose a Markdown engine or classify prose.
+Native selection belongs to the library's text view. Keep an assistant message in one row so selection can cross paragraphs, headings and lists. Code blocks and tables use the library's native views and their selection behavior. Web uses browser selection over semantic HTML. Once its WASM parser is initialized, the library parses synchronously for the first commit of each mounted row; an empty interim row would corrupt virtualized measurements and move the reader. Chat owns paced reveal, the web render cap, message identity and list measurement. Native receives complete messages.
 
 ## Links and images
 

packages/app/e2e/browser/assistant-message-render-limit.spec.ts

@@ -2,7 +2,9 @@ import { expect, test } from "../support/fixtures";
 import { getUtf8ByteLength } from "../../src/components/assistant-message-render-limit";
 import { openAgentRoute, seedMockAgentWorkspace } from "../support/helpers/mock-agent";
 
-test("caps a newline-heavy assistant message before rendering markdown", async ({ page }) => {
+test("caps a newline-heavy assistant message on web before rendering markdown", async ({
+  page,
+}) => {
   const hiddenTail = "HIDDEN_OVERSIZED_MESSAGE_TAIL";
   const response = `${"x\n".repeat(16_000)}${hiddenTail}`;
   const agent = await seedMockAgentWorkspace({

packages/app/src/components/assistant-message-render-limit.native.ts

@@ -0,0 +1,11 @@
+import type { CappedAssistantMessage } from "./assistant-message-render-limit.shared";
+export {
+  getUtf8ByteLength,
+  type CappedAssistantMessage,
+} from "./assistant-message-render-limit.shared";
+
+// Native passes a single string to the C++ parser, without the web renderer's
+// React-node fan-out. Keep complete messages selectable across all paragraphs.
+export function capAssistantMessageForRender(message: string): CappedAssistantMessage {
+  return { text: message, capped: false };
+}

packages/app/src/components/assistant-message-render-limit.shared.ts

@@ -0,0 +1,30 @@
+export interface CappedAssistantMessage {
+  text: string;
+  capped: boolean;
+}
+
+export function getUtf8ByteLength(message: string): number {
+  let bytes = 0;
+
+  for (let index = 0; index < message.length; index += 1) {
+    const codeUnit = message.charCodeAt(index);
+    if (codeUnit < 0x80) {
+      bytes += 1;
+    } else if (codeUnit < 0x800) {
+      bytes += 2;
+    } else if (
+      codeUnit >= 0xd800 &&
+      codeUnit <= 0xdbff &&
+      index + 1 < message.length &&
+      message.charCodeAt(index + 1) >= 0xdc00 &&
+      message.charCodeAt(index + 1) <= 0xdfff
+    ) {
+      bytes += 4;
+      index += 1;
+    } else {
+      bytes += 3;
+    }
+  }
+
+  return bytes;
+}

packages/app/src/components/assistant-message-render-limit.test.ts

@@ -56,3 +56,11 @@ describe("assistant message render limit", () => {
     });
   });
 });
+
+it("preserves complete native multi-paragraph messages and the newline-heavy repro", async () => {
+  const native = await import("./assistant-message-render-limit.native");
+  const message = "Paragraph.\n\n".repeat(3000) + "Section 60";
+  expect(native.capAssistantMessageForRender(message)).toEqual({ text: message, capped: false });
+  const lines = "x\n".repeat(16_000) + "HIDDEN_OVERSIZED_MESSAGE_TAIL";
+  expect(native.capAssistantMessageForRender(lines)).toEqual({ text: lines, capped: false });
+});

packages/app/src/components/assistant-message-render-limit.ts

@@ -1,55 +1 @@
-const graphemeSegmenter =
-  typeof Intl.Segmenter === "function"
-    ? new Intl.Segmenter(undefined, { granularity: "grapheme" })
-    : null;
-
-export const ASSISTANT_MESSAGE_RENDER_CHARACTER_LIMIT = 32_000;
-
-export interface CappedAssistantMessage {
-  text: string;
-  capped: boolean;
-}
-
-export function getUtf8ByteLength(message: string): number {
-  let bytes = 0;
-
-  for (let index = 0; index < message.length; index += 1) {
-    const codeUnit = message.charCodeAt(index);
-    if (codeUnit < 0x80) {
-      bytes += 1;
-    } else if (codeUnit < 0x800) {
-      bytes += 2;
-    } else if (
-      codeUnit >= 0xd800 &&
-      codeUnit <= 0xdbff &&
-      index + 1 < message.length &&
-      message.charCodeAt(index + 1) >= 0xdc00 &&
-      message.charCodeAt(index + 1) <= 0xdfff
-    ) {
-      bytes += 4;
-      index += 1;
-    } else {
-      bytes += 3;
-    }
-  }
-
-  return bytes;
-}
-
-export function capAssistantMessageForRender(message: string): CappedAssistantMessage {
-  if (message.length <= ASSISTANT_MESSAGE_RENDER_CHARACTER_LIMIT) {
-    return { text: message, capped: false };
-  }
-
-  let end = ASSISTANT_MESSAGE_RENDER_CHARACTER_LIMIT;
-  if (graphemeSegmenter) {
-    end = graphemeSegmenter.segment(message).containing(end)!.index;
-  } else {
-    const finalCodeUnit = message.charCodeAt(end - 1);
-    if (finalCodeUnit >= 0xd800 && finalCodeUnit <= 0xdbff) {
-      end -= 1;
-    }
-  }
-
-  return { text: message.slice(0, end), capped: true };
-}
+export * from "./assistant-message-render-limit.web";

packages/app/src/components/assistant-message-render-limit.web.ts

@@ -0,0 +1,30 @@
+import type { CappedAssistantMessage } from "./assistant-message-render-limit.shared";
+export {
+  getUtf8ByteLength,
+  type CappedAssistantMessage,
+} from "./assistant-message-render-limit.shared";
+
+const graphemeSegmenter =
+  typeof Intl.Segmenter === "function"
+    ? new Intl.Segmenter(undefined, { granularity: "grapheme" })
+    : null;
+
+export const ASSISTANT_MESSAGE_RENDER_CHARACTER_LIMIT = 32_000;
+
+export function capAssistantMessageForRender(message: string): CappedAssistantMessage {
+  if (message.length <= ASSISTANT_MESSAGE_RENDER_CHARACTER_LIMIT) {
+    return { text: message, capped: false };
+  }
+
+  let end = ASSISTANT_MESSAGE_RENDER_CHARACTER_LIMIT;
+  if (graphemeSegmenter) {
+    end = graphemeSegmenter.segment(message).containing(end)!.index;
+  } else {
+    const finalCodeUnit = message.charCodeAt(end - 1);
+    if (finalCodeUnit >= 0xd800 && finalCodeUnit <= 0xdbff) {
+      end -= 1;
+    }
+  }
+
+  return { text: message.slice(0, end), capped: true };
+}