fix(chat): close nested-list streaming cursor reflow

apps/desktop/src/features/chat/transcript/AssistantTurnParts.tsx

@@ -19,7 +19,7 @@ const SmoothMessageBubble = memo(function SmoothMessageBubble({ message, streami
     window.matchMedia("(prefers-reduced-motion: reduce)").matches;
   const enabled = smoothStreaming && !prefersReducedMotion;
   const displayContent = useSmoothText(message.content || "", streaming, enabled);
-  const showCursor = streaming && enabled && (displayContent.length < (message.content || "").length);
+  const showCursor = streaming && enabled && Boolean(displayContent);
   return (
     <div
       className={`message-bubble assistant-turn-fragment${streaming ? " streaming" : ""}${showCursor ? " smooth-cursor" : ""}`}

apps/desktop/src/styles/messages.css

@@ -3275,14 +3275,22 @@
   font-size: var(--text-sm);
 }
 
-/* ── Smooth streaming cursor ── */
+/* ── Smooth streaming cursor and layout stabilization ── */
 
 @keyframes smooth-stream-blink {
   0%, 100% { opacity: 1; }
   50% { opacity: 0; }
 }
 
-.assistant-turn-fragment.smooth-cursor .prose-chat > :last-child::after {
+.assistant-turn-fragment.streaming .prose-chat {
+  text-wrap: wrap;
+}
+
+.assistant-turn-fragment.smooth-cursor .prose-chat > :last-child:not(ul):not(ol):not(blockquote):not(pre):not(table):not(.table-wrap)::after,
+.assistant-turn-fragment.smooth-cursor .prose-chat > :is(ul, ol):last-child li:last-child:not(:has(ul, ol)):not(:has(p))::after,
+.assistant-turn-fragment.smooth-cursor .prose-chat > :is(ul, ol):last-child li:last-child > p:last-child::after,
+.assistant-turn-fragment.smooth-cursor .prose-chat > blockquote:last-child > p:last-child::after,
+.assistant-turn-fragment.smooth-cursor .prose-chat > pre:last-child > code::after {
   content: "";
   display: inline-block;
   width: 2px;
@@ -3294,7 +3302,11 @@
 }
 
 @media (prefers-reduced-motion: reduce) {
-  .assistant-turn-fragment.smooth-cursor .prose-chat > :last-child::after {
+  .assistant-turn-fragment.smooth-cursor .prose-chat > :last-child:not(ul):not(ol):not(blockquote):not(pre):not(table):not(.table-wrap)::after,
+  .assistant-turn-fragment.smooth-cursor .prose-chat > :is(ul, ol):last-child li:last-child:not(:has(ul, ol)):not(:has(p))::after,
+  .assistant-turn-fragment.smooth-cursor .prose-chat > :is(ul, ol):last-child li:last-child > p:last-child::after,
+  .assistant-turn-fragment.smooth-cursor .prose-chat > blockquote:last-child > p:last-child::after,
+  .assistant-turn-fragment.smooth-cursor .prose-chat > pre:last-child > code::after {
     animation: none;
     opacity: 0.7;
   }

apps/desktop/test/chat-streaming-layout.test.mjs

@@ -0,0 +1,48 @@
+import assert from "node:assert/strict";
+import { readFile } from "node:fs/promises";
+import test from "node:test";
+
+const assistantTurnPartsSource = await readFile(
+  new URL("../src/features/chat/transcript/AssistantTurnParts.tsx", import.meta.url),
+  "utf8",
+);
+const messagesCss = await readFile(
+  new URL("../src/styles/messages.css", import.meta.url),
+  "utf8",
+);
+
+test("streaming cursor remains steady throughout active streaming without flapping", () => {
+  // Must not flap on/off between network chunks when buffer catches up with current source length
+  assert.match(
+    assistantTurnPartsSource,
+    /const showCursor = streaming && enabled && Boolean\(displayContent\);/,
+  );
+  assert.doesNotMatch(
+    assistantTurnPartsSource,
+    /displayContent\.length < \(message\.content \|\| ""\)\.length/,
+  );
+});
+
+test("streaming prose chat stabilizes line wrapping against orphan-rebalancing reflow", () => {
+  assert.match(
+    messagesCss,
+    /\.assistant-turn-fragment\.streaming \.prose-chat\s*\{\s*text-wrap:\s*wrap;\s*\}/,
+  );
+});
+
+test("streaming cursor attaches to inline leaf blocks and list items instead of container lists", () => {
+  // List cursor must be placed on inline content, never on nested ul/ol containers.
+  assert.match(
+    messagesCss,
+    /\.assistant-turn-fragment\.smooth-cursor \.prose-chat > :is\(ul, ol\):last-child li:last-child:not\(:has\(ul, ol\)\):not\(:has\(p\)\)::after/,
+  );
+  assert.match(
+    messagesCss,
+    /\.assistant-turn-fragment\.smooth-cursor \.prose-chat > :is\(ul, ol\):last-child li:last-child > p:last-child::after/,
+  );
+  assert.doesNotMatch(messagesCss, /li:last-child > :last-child::after/);
+  assert.match(
+    messagesCss,
+    /\.assistant-turn-fragment\.smooth-cursor \.prose-chat > :last-child:not\(ul\):not\(ol\)/,
+  );
+});

docs/spec/04-ux/09-interaction-patterns.md

@@ -653,7 +653,10 @@ may be retained while exactly one workspace supplies the visible shell context.
   approaches the viewport; thinking disclosures always retain Mermaid source.
 - Diagram render failure or the 20,000-character / 500-edge safety limit keeps
   the source visible and copyable instead of failing the assistant turn.
-- Cursor indicator: subtle pulsing accent dot or line at the end of streaming content
+- Cursor indicator: subtle pulsing accent line at the end of streaming inline
+  content. For Markdown lists and quotes, attach it to the terminal paragraph
+  or text leaf; never append it to a nested list container, which creates an
+  extra line box and shifts content while the response streams.
 - Before the first assistant or tool event, the active turn shows one compact
   localized `Working…` status with elapsed time. When the runtime reports a
   quiet interval, that same row names the wait: starting, waiting for the

docs/spec/06-delivery/04-e2e-test-plan.md

@@ -6013,6 +6013,9 @@ must keep splitting are covered by `markdown-blocks.test.mjs`.
     jump-to-latest appears as soon as follow mode is released.
   - On send, the transcript re-pins, hides jump-to-latest, and jumps to the bottom so the new user message (and following stream) is visible.
   - Streaming continues to follow while pinned.
+  - Long Markdown responses with nested lists keep their list container line
+    boxes stable during streaming; the cursor follows the terminal inline text
+    without adding a blank line below a nested list.
   - Manual scroll mid-stream pauses follow and shows jump-to-latest again; clicking it resumes follow.
 - **Specs linked**: `04-ux/08-component-spec.md`, `04-ux/09-interaction-patterns.md`
 - **Acceptance**: C (chat stream), Quality / D151