diff --git a/.project-docs/30-worklog/tasks/20260831-show-progress-messages-a14f9c2d.md b/.project-docs/30-worklog/tasks/20260831-show-progress-messages-a14f9c2d.md
new file mode 100644
index 0000000..cfef58e
--- /dev/null
+++ b/.project-docs/30-worklog/tasks/20260831-show-progress-messages-a14f9c2d.md
@@ -0,0 +1,84 @@
+# Task: Show assistant progress messages
+
+## Identity
+
+- Task ID: 20260831-show-progress-messages-a14f9c2d
+- Mode: Feature
+- Branch: codex/20260831-show-progress-messages-a14f9c2d-show-progress-messages-a14f9c2d
+- Worktree: /Users/inmanx/Documents/makelore-show-progress-messages-a14f9c2d
+- Base commit: 38f85f6b5e4dc4e2c5e5b9f8f4506554cfd578f5
+- Owner: codex
+- Status: Ready for Integration
+
+## Scope
+
+- Identify the protocol and UI classification of assistant text emitted before
+  or between tool calls, using the supplied screenshot only as a visual example.
+- Verify that this stage/progress narration is projected and rendered in the
+  current Makelore Code timeline without exposing Pi-private wire types.
+- Preserve per-item expand/collapse after a stage explanation has completed,
+  including after the enclosing turn has settled.
+- Make every collapsed thinking, stage-explanation, and tool-output preview
+  start from its first visible block and line, including horizontally
+  overflowing text.
+
+## Intent And Constraints
+
+- Preserve the product-neutral `ConversationMessageNode` / Snapshot / Patch
+  contract and the Main-owned Pi boundary.
+- Keep private reasoning distinct from user-visible assistant narration and
+  tool execution output.
+- Do not modify the occupied primary worktree or the separate running
+  development worktree.
+
+## Outcome
+
+- Confirmed the raw message is an ordinary Pi assistant message whose turn ends
+  with `stopReason: toolUse`; Main normalizes it to an assistant
+  `ConversationMessageNode` with `stopReason: tool-use`.
+- Confirmed the Renderer semantically projects non-final assistant text as
+  `assistant-commentary` / “过程说明”, rather than treating it as hidden
+  thinking or as a tool node.
+- Confirmed active process groups open automatically and show a compact
+  one-line stage explanation with an expand control; settled process groups
+  retain the explanation behind their collapsed process summary while the
+  final assistant answer remains visible.
+- Added explicit regression coverage proving a completed stage explanation
+  remains collapsed to its first line by default, retains its own expand
+  control, reveals the complete Markdown body, and can be collapsed again.
+- Changed collapsed process preview selection to use the first displayable
+  block and first non-empty line for thinking, assistant commentary, and tool
+  output. Long lines retain their beginning and use a trailing ellipsis.
+- Kept every collapsed preview viewport at horizontal offset zero on content
+  and size changes. Tail-only streaming updates no longer replace or replay an
+  unchanged head preview, while expanded content remains complete.
+
+## Verification
+
+- Installed the existing lockfile with pinned pnpm `10.33.4`; 1,015 packages
+  were reused from the local store and no manifest or lockfile changed.
+- Focused Vitest passed: 3 files / 28 tests covering live Pi event projection,
+  durable session hydration, and Coding timeline process/commentary rendering.
+- Follow-up focused Vitest passed: 1 file / 9 tests, including completed
+  commentary expand/collapse and stable head-preview assertions across
+  streaming updates.
+- `pnpm run typecheck`: passed.
+- Scoped ESLint for the changed Renderer, unit, and Electron E2E files: passed.
+- `pnpm run build:vite`: passed; only the repository's existing dynamic-import
+  and bundle-size warnings were emitted.
+- Focused Electron Playwright E2E passed: 1 file / 2 tests, including first-line
+  thinking display, head truncation, and a measured tool-preview
+  `scrollLeft` of zero.
+- Inspected `electron/coding-runtime/pi/event-projector.ts`,
+  `electron/coding-runtime/pi/session-projector.ts`,
+  `shared/coding-conversation-contracts.ts`, and
+  `src/pages/Chat/CodingConversationTimeline.tsx` across the complete
+  classification path.
+
+## Follow-ups
+
+- None.
+
+## Promotion Candidates
+
+- None recorded.
diff --git a/src/pages/Chat/CodingConversationTimeline.tsx b/src/pages/Chat/CodingConversationTimeline.tsx
index 2a82f2c..e4e407f 100644
--- a/src/pages/Chat/CodingConversationTimeline.tsx
+++ b/src/pages/Chat/CodingConversationTimeline.tsx
@@ -72,7 +72,6 @@ const WINDOW_STEP = 100;
 const LONG_OUTPUT_CHARS = 4_000;
 const STREAMING_THINKING_WINDOW_CHARS = 16_000;
 const PROGRESS_PREVIEW_MAX_CHARS = 360;
-const PROGRESS_ROLL_CHAR_STEP = 6;
 
 const NODE_STATUS_LABELS: Record<string, string> = {
   declared: '已声明',
@@ -652,19 +651,19 @@ function toolActivityIcon(node: ConversationToolNode) {
   return <Hammer className={className} aria-hidden="true" />;
 }
 
-function latestProgressLine(value: string): string | null {
+function firstProgressLine(value: string): string | null {
   const lines = value
     .split(/\r?\n/)
     .map((line) => line.trim())
     .filter(Boolean);
   const line = lines
-    .at(-1)
+    .at(0)
     ?.replace(/\s+/g, ' ')
     .replace(/^#{1,6}\s+/, '')
     .replace(/^(?:[-*+]|\d+[.)])\s+/, '');
   if (!line) return null;
   return line.length > PROGRESS_PREVIEW_MAX_CHARS
-    ? `…${line.slice(-(PROGRESS_PREVIEW_MAX_CHARS - 1))}`
+    ? `${line.slice(0, PROGRESS_PREVIEW_MAX_CHARS - 1)}…`
     : line;
 }
 
@@ -699,22 +698,20 @@ const RollingProgressPreview = memo(function RollingProgressPreview({
   codeClassName?: string;
 }) {
   const viewportRef = useRef<HTMLSpanElement | null>(null);
-  const revision = `${active ? 'active' : 'settled'}:${Math.floor(
-    contentVersion / PROGRESS_ROLL_CHAR_STEP,
-  )}`;
+  const revision = `${active ? 'active' : 'settled'}:${text}`;
   const parts = progressInlineParts(text);
 
   useLayoutEffect(() => {
     const viewport = viewportRef.current;
     if (!viewport) return;
-    viewport.scrollLeft = viewport.scrollWidth;
+    viewport.scrollLeft = 0;
   }, [contentVersion, text]);
 
   useEffect(() => {
     const viewport = viewportRef.current;
     if (!viewport || typeof ResizeObserver === 'undefined') return;
     const observer = new ResizeObserver(() => {
-      viewport.scrollLeft = viewport.scrollWidth;
+      viewport.scrollLeft = 0;
     });
     observer.observe(viewport);
     return () => observer.disconnect();
@@ -729,9 +726,9 @@ const RollingProgressPreview = memo(function RollingProgressPreview({
         className,
       )}
       data-progress-alignment="left"
+      data-progress-origin="head"
       data-progress-update-motion={rollUpdates ? 'roll' : 'none'}
       data-progress-shimmer={active && shimmer ? 'true' : 'false'}
-      data-progress-tail="true"
       data-roll-revision={rollUpdates ? revision : undefined}
       data-testid={testId}
       title={text}
@@ -772,11 +769,11 @@ function contentBlocksProgressPreview(
   blocks: ConversationContentBlock[],
   fallback: string,
 ): string {
-  for (let index = blocks.length - 1; index >= 0; index -= 1) {
+  for (let index = 0; index < blocks.length; index += 1) {
     const block = blocks[index];
     if (!block) continue;
     if (block.kind === 'image') return '图片附件';
-    const preview = latestProgressLine(block.text);
+    const preview = firstProgressLine(block.text);
     if (preview) return preview;
   }
   return fallback;
@@ -823,14 +820,14 @@ function toolDetailsProgress(details: KnownToolDetails | undefined): string | nu
 }
 
 function toolProgressPreview(node: ConversationToolNode): string {
-  for (let index = node.output.length - 1; index >= 0; index -= 1) {
+  for (let index = 0; index < node.output.length; index += 1) {
     const block = node.output[index];
     if (!block) continue;
     if (block.kind === 'image') return '已生成图片附件';
-    const outputPreview = latestProgressLine(block.text);
+    const outputPreview = firstProgressLine(block.text);
     if (outputPreview) return outputPreview;
   }
-  return latestProgressLine(node.inputText)
+  return firstProgressLine(node.inputText)
     ?? toolDetailsProgress(node.details)
     ?? statusLabel(node.status);
 }
@@ -1150,7 +1147,7 @@ const ProcessThinking = memo(function ProcessThinking({
         streaming={streaming}
         rollUpdates={false}
         contentVersion={block.text.length}
-        preview={latestProgressLine(block.text) ?? (
+        preview={firstProgressLine(block.text) ?? (
           streaming ? 'Pi 正在形成思路…' : '思考已完成'
         )}
       >
diff --git a/tests/e2e/pi-coding-first-chat.spec.ts b/tests/e2e/pi-coding-first-chat.spec.ts
index b8fad8d..62ff4ad 100644
--- a/tests/e2e/pi-coding-first-chat.spec.ts
+++ b/tests/e2e/pi-coding-first-chat.spec.ts
@@ -215,7 +215,7 @@ async function installCodingFirstChatHost(
           output: [{
             kind: 'text',
             id: 'browser-output-e2e',
-            text: `${'Checking browser runtime state and the latest navigation checkpoint. '.repeat(5)}Browser ready`,
+            text: `${'Checking browser runtime state and the latest navigation checkpoint. '.repeat(8)}Browser ready`,
             status: 'complete',
           }],
           details: { schema: 'agent-browser.v1', action: 'status' },
@@ -689,13 +689,13 @@ test('PI feature UI isolates Conversations and exposes queue, interaction, model
     await expect(activeProcess).toHaveAttribute('open', '');
     await expect(activeProcess.locator('summary').first()).toContainText('处理中');
     const activeThinking = page.getByLabel('思考过程');
-    await expect(activeThinking).toContainText('Preparing the smallest safe next step.');
-    await expect(activeThinking).not.toContainText('Inspecting the project before responding.');
+    await expect(activeThinking).toContainText('Inspecting the project before responding.');
+    await expect(activeThinking).not.toContainText('Preparing the smallest safe next step.');
     await expect(activeThinking).toHaveAttribute('data-collapsed-lines', '1');
     await expect(activeThinking).toHaveAttribute('data-expanded', 'false');
     await expect(activeThinking).toHaveAttribute('data-streaming', 'true');
     const activeThinkingPreview = activeThinking.getByTestId('process-progress-preview');
-    await expect(activeThinkingPreview).toHaveAttribute('data-progress-tail', 'true');
+    await expect(activeThinkingPreview).toHaveAttribute('data-progress-origin', 'head');
     await expect(activeThinkingPreview).toHaveAttribute('data-progress-alignment', 'left');
     await expect(activeThinkingPreview).toHaveAttribute('data-progress-update-motion', 'none');
     await expect(activeThinkingPreview).not.toHaveAttribute('data-roll-revision');
@@ -727,6 +727,7 @@ test('PI feature UI isolates Conversations and exposes queue, interaction, model
     await expect(activeCommentary).toHaveClass(/text-foreground/);
     const activeCommentaryPreview = activeCommentary.getByTestId('process-progress-preview');
     await expect(activeCommentaryPreview).toContainText('Durable assistant response');
+    await expect(activeCommentaryPreview).toHaveAttribute('data-progress-origin', 'head');
     await expect(activeCommentaryPreview).toHaveClass(/text-foreground/);
     await expect(activeCommentaryPreview).not.toHaveClass(/text-muted-foreground/);
     await expect(activeCommentaryPreview).toHaveAttribute('data-progress-shimmer', 'false');
@@ -745,9 +746,11 @@ test('PI feature UI isolates Conversations and exposes queue, interaction, model
     const compactToolSummary = compactTool.locator('> summary');
     await expect(compactTool).not.toHaveAttribute('open', '');
     await expect(compactToolSummary).toHaveAttribute('data-collapsed-lines', '1');
-    await expect(compactTool.getByTestId('tool-progress-preview')).toContainText('Browser ready');
     await expect(compactTool.getByTestId('tool-progress-preview'))
-      .toHaveAttribute('data-progress-tail', 'true');
+      .toContainText('Checking browser runtime state');
+    await expect(compactTool.getByTestId('tool-progress-preview')).not.toContainText('Browser ready');
+    await expect(compactTool.getByTestId('tool-progress-preview'))
+      .toHaveAttribute('data-progress-origin', 'head');
     const toolProgressViewport = compactTool.getByTestId('tool-progress-preview');
     await expect(toolProgressViewport).toHaveAttribute('data-progress-alignment', 'left');
     await expect(toolProgressViewport).toHaveAttribute('data-progress-shimmer', 'false');
@@ -759,10 +762,7 @@ test('PI feature UI isolates Conversations and exposes queue, interaction, model
       scrollWidth: element.scrollWidth,
     }));
     expect(toolProgressScroll.scrollWidth).toBeGreaterThan(toolProgressScroll.clientWidth);
-    expect(Math.abs(
-      toolProgressScroll.scrollLeft
-        - (toolProgressScroll.scrollWidth - toolProgressScroll.clientWidth),
-    )).toBeLessThanOrEqual(2);
+    expect(Math.abs(toolProgressScroll.scrollLeft)).toBeLessThanOrEqual(2);
     const compactToolBounds = await compactToolSummary.boundingBox();
     expect(compactToolBounds).not.toBeNull();
     expect(compactToolBounds!.height).toBeLessThanOrEqual(33);
diff --git a/tests/unit/coding-conversation-timeline.test.tsx b/tests/unit/coding-conversation-timeline.test.tsx
index 6bef893..9940b6e 100644
--- a/tests/unit/coding-conversation-timeline.test.tsx
+++ b/tests/unit/coding-conversation-timeline.test.tsx
@@ -303,8 +303,8 @@ describe('CodingConversationTimeline', () => {
     expect(within(process).getByText('处理中')).toBeVisible();
     const thinking = screen.getByLabelText('思考过程');
     const thinkingPreview = within(thinking).getByTestId('process-progress-preview');
-    expect(thinkingPreview).toHaveTextContent('最后确认本轮只读取、不修改项目内容。');
-    expect(thinkingPreview).toHaveAttribute('data-progress-tail', 'true');
+    expect(thinkingPreview).toHaveTextContent('先确认 project.json 项目边界，再读取配置。');
+    expect(thinkingPreview).toHaveAttribute('data-progress-origin', 'head');
     expect(thinkingPreview).toHaveAttribute('data-progress-alignment', 'left');
     expect(thinkingPreview).toHaveAttribute('data-progress-update-motion', 'none');
     expect(thinkingPreview).not.toHaveAttribute('data-roll-revision');
@@ -315,7 +315,7 @@ describe('CodingConversationTimeline', () => {
     expect(thinkingPreview).toHaveClass('text-left');
     expect(thinkingPreview.firstElementChild).toHaveClass('inline-flex');
     expect(thinkingPreview.firstElementChild).not.toHaveClass('absolute', 'right-0');
-    expect(thinking).not.toHaveTextContent('先确认 project.json 项目边界，再读取配置。');
+    expect(thinking).not.toHaveTextContent('最后确认本轮只读取、不修改项目内容。');
     expect(thinking).toHaveAttribute('data-collapsed-lines', '1');
     expect(thinking).toHaveAttribute('data-expanded', 'false');
     expect(thinking).toHaveAttribute('data-streaming', 'true');
@@ -340,19 +340,19 @@ describe('CodingConversationTimeline', () => {
     expect(processNote).toHaveAttribute('data-collapsed-lines', '1');
     expect(processNote).toHaveClass('max-h-[1.65em]', 'overflow-hidden');
     const commentaryPreview = within(processNote).getByTestId('process-progress-preview');
-    expect(commentaryPreview).toHaveTextContent('让我看看 index.html 当前的实际内容：');
+    expect(commentaryPreview).toHaveTextContent('好的，两件事都办：先再试一次产品素材服务，然后整体优化手机移动端体验。');
+    expect(commentaryPreview).toHaveAttribute('data-progress-origin', 'head');
     expect(commentaryPreview).toHaveClass('text-foreground');
     expect(commentaryPreview).not.toHaveClass('text-muted-foreground/75');
-    expect(within(commentaryPreview).getByText('index.html')).toHaveClass('text-foreground');
-    expect(within(commentaryPreview).getByText('index.html')).not.toHaveClass('text-muted-foreground');
     expect(commentaryPreview).toHaveAttribute('data-progress-shimmer', 'false');
     expect(commentaryPreview).toHaveAttribute('data-progress-update-motion', 'none');
     expect(commentaryPreview).not.toHaveAttribute('data-roll-revision');
     expect(commentaryPreview.querySelector('.streaming-progress-shimmer')).not.toBeInTheDocument();
     expect(commentaryPreview.querySelector('.streaming-progress-roll')).not.toBeInTheDocument();
-    expect(processNote).not.toHaveTextContent('好的，两件事都办');
+    expect(processNote).not.toHaveTextContent('让我看看 index.html 当前的实际内容：');
     fireEvent.click(screen.getByRole('button', { name: '展开过程说明' }));
     expect(screen.getByText(/好的，两件事都办/).closest('[data-testid="coding-process-group"]')).toBe(process);
+    expect(within(processNote).getByText('index.html').tagName).toBe('CODE');
     expect(within(processNote).getByTestId('assistant-markdown')).toHaveClass('text-foreground');
     expect(within(processNote).getByTestId('assistant-markdown')).not.toHaveClass('text-muted-foreground');
     fireEvent.click(screen.getByRole('button', { name: '收起过程说明' }));
@@ -362,8 +362,8 @@ describe('CodingConversationTimeline', () => {
     expect(tool.querySelector('summary')).toHaveClass('h-8', 'overflow-hidden');
     const toolPreview = within(tool).getByTestId('tool-progress-preview');
     const initialToolRevision = toolPreview.getAttribute('data-roll-revision');
-    expect(toolPreview).toHaveTextContent('正在读取入口文件…');
-    expect(toolPreview).toHaveAttribute('data-progress-tail', 'true');
+    expect(toolPreview).toHaveTextContent('已定位项目根目录');
+    expect(toolPreview).toHaveAttribute('data-progress-origin', 'head');
     expect(toolPreview).toHaveAttribute('data-progress-alignment', 'left');
     expect(toolPreview).toHaveAttribute('data-progress-update-motion', 'roll');
     expect(toolPreview).toHaveAttribute('data-progress-shimmer', 'true');
@@ -387,21 +387,21 @@ describe('CodingConversationTimeline', () => {
     }));
 
     expect(within(thinking).getByTestId('process-progress-preview'))
-      .toHaveTextContent('正在确认最新入口 main.ts。');
+      .toHaveTextContent('先确认 project.json 项目边界，再读取配置。');
     expect(within(thinking).getByTestId('process-progress-preview'))
       .not.toHaveAttribute('data-roll-revision');
     expect(within(thinking).getByTestId('process-progress-preview')
       .querySelector('.streaming-progress-roll')).not.toBeInTheDocument();
     expect(within(processNote).getByTestId('process-progress-preview'))
-      .toHaveTextContent('正在整理最新结论。');
+      .toHaveTextContent('好的，两件事都办：先再试一次产品素材服务，然后整体优化手机移动端体验。');
     expect(within(processNote).getByTestId('process-progress-preview'))
       .toHaveClass('text-foreground');
     expect(within(processNote).getByTestId('process-progress-preview'))
       .toHaveAttribute('data-progress-shimmer', 'false');
     expect(within(tool).getByTestId('tool-progress-preview'))
-      .toHaveTextContent('正在追踪最新工具输出：main.ts 已读取。');
-    expect(within(tool).getByTestId('tool-progress-preview'))
-      .not.toHaveAttribute('data-roll-revision', initialToolRevision);
+      .toHaveTextContent('已定位项目根目录');
+    expect(within(tool).getByTestId('tool-progress-preview').getAttribute('data-roll-revision'))
+      .toBe(initialToolRevision);
 
     fireEvent.click(tool.querySelector('summary')!);
     await waitFor(() => expect(tool).toHaveAttribute('open'));
@@ -447,7 +447,12 @@ describe('CodingConversationTimeline', () => {
           stopReason: 'tool-use' as const,
           blocks: [
             { kind: 'thinking' as const, id: 'thinking-completed-process', text: '先读取配置，再核对入口。', status: 'streaming' as const },
-            { kind: 'text' as const, id: 'preamble-completed-process', text: '我先检查项目配置。', status: 'complete' as const },
+            {
+              kind: 'text' as const,
+              id: 'preamble-completed-process',
+              text: '我先检查项目配置。\n\n现在开始核对 `index.html` 入口文件。',
+              status: 'complete' as const,
+            },
           ],
         },
         {
@@ -502,6 +507,29 @@ describe('CodingConversationTimeline', () => {
       .toHaveAttribute('data-progress-shimmer', 'false');
     expect(within(settledThinking).getByTestId('process-progress-preview')
       .querySelector('.streaming-progress-shimmer')).not.toBeInTheDocument();
+    const completedCommentary = document.querySelector(
+      '[data-node-id="message-work-completed-process"][data-node-kind="assistant-commentary"]',
+    )!;
+    const completedCommentaryViewport = within(completedCommentary as HTMLElement)
+      .getByLabelText('过程说明');
+    expect(completedCommentaryViewport).toHaveAttribute('data-streaming', 'false');
+    expect(completedCommentaryViewport).toHaveAttribute('data-expanded', 'false');
+    expect(within(completedCommentaryViewport).getByTestId('process-progress-preview'))
+      .toHaveTextContent('我先检查项目配置。');
+    expect(within(completedCommentaryViewport).getByTestId('process-progress-preview'))
+      .toHaveAttribute('data-progress-origin', 'head');
+    expect(completedCommentaryViewport).not.toHaveTextContent('现在开始核对 index.html 入口文件。');
+    const completedCommentaryToggle = within(completedCommentary as HTMLElement)
+      .getByRole('button', { name: '展开过程说明' });
+    expect(completedCommentaryToggle).toHaveAttribute('aria-expanded', 'false');
+    fireEvent.click(completedCommentaryToggle);
+    expect(completedCommentaryViewport).toHaveAttribute('data-expanded', 'true');
+    expect(completedCommentaryViewport).toHaveTextContent('我先检查项目配置。');
+    expect(completedCommentaryViewport).toHaveTextContent('现在开始核对 index.html 入口文件。');
+    expect(within(completedCommentaryViewport).getByText('index.html').tagName).toBe('CODE');
+    fireEvent.click(within(completedCommentary as HTMLElement)
+      .getByRole('button', { name: '收起过程说明' }));
+    expect(completedCommentaryViewport).toHaveAttribute('data-expanded', 'false');
     const tool = screen.getByText('读取项目配置').closest('details')!;
     expect(tool).not.toHaveAttribute('open');
     fireEvent.click(tool.querySelector('summary')!);