レビュー画面に元のタスク指示を表示 & タイムスタンプ短縮

- getOriginalInstruction: ブランチ最初のコミットから元の指示を抽出
- /review-tasks の選択肢と詳細表示に元の指示を追加
- タイムスタンプのハイフンを除去 (2026-01-29T0225 → 20260129T0225)

src/__tests__/getOriginalInstruction.test.ts

@@ -0,0 +1,97 @@
+/**
+ * Tests for getOriginalInstruction
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+// Mock child_process.execFileSync
+vi.mock('node:child_process', () => ({
+  execFileSync: vi.fn(),
+}));
+
+import { execFileSync } from 'node:child_process';
+const mockExecFileSync = vi.mocked(execFileSync);
+
+import { getOriginalInstruction } from '../task/worktree.js';
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe('getOriginalInstruction', () => {
+  it('should extract instruction from takt-prefixed commit message', () => {
+    mockExecFileSync.mockReturnValue('takt: 認証機能を追加する\ntakt: fix-auth\n');
+
+    const result = getOriginalInstruction('/project', 'main', 'takt/20260128-fix-auth');
+
+    expect(result).toBe('認証機能を追加する');
+    expect(mockExecFileSync).toHaveBeenCalledWith(
+      'git',
+      ['log', '--format=%s', '--reverse', 'main..takt/20260128-fix-auth'],
+      expect.objectContaining({ cwd: '/project', encoding: 'utf-8' }),
+    );
+  });
+
+  it('should return first commit message without takt prefix if not present', () => {
+    mockExecFileSync.mockReturnValue('Initial implementation\n');
+
+    const result = getOriginalInstruction('/project', 'main', 'takt/20260128-fix-auth');
+
+    expect(result).toBe('Initial implementation');
+  });
+
+  it('should return empty string when no commits on branch', () => {
+    mockExecFileSync.mockReturnValue('');
+
+    const result = getOriginalInstruction('/project', 'main', 'takt/20260128-fix-auth');
+
+    expect(result).toBe('');
+  });
+
+  it('should return empty string when git command fails', () => {
+    mockExecFileSync.mockImplementation(() => {
+      throw new Error('not a git repository');
+    });
+
+    const result = getOriginalInstruction('/non-existent', 'main', 'takt/20260128-fix-auth');
+
+    expect(result).toBe('');
+  });
+
+  it('should handle multi-line commit messages (use only first line)', () => {
+    mockExecFileSync.mockReturnValue('takt: Fix the login bug\ntakt: follow-up fix\n');
+
+    const result = getOriginalInstruction('/project', 'main', 'takt/20260128-fix-login');
+
+    expect(result).toBe('Fix the login bug');
+  });
+
+  it('should return empty string when takt prefix has no content', () => {
+    // "takt: \n" trimmed → "takt:", starts with "takt:" → slice + trim → ""
+    mockExecFileSync.mockReturnValue('takt: \n');
+
+    const result = getOriginalInstruction('/project', 'main', 'takt/20260128-task');
+
+    expect(result).toBe('');
+  });
+
+  it('should return instruction text when takt prefix has content', () => {
+    mockExecFileSync.mockReturnValue('takt: add search feature\n');
+
+    const result = getOriginalInstruction('/project', 'main', 'takt/20260128-task');
+
+    expect(result).toBe('add search feature');
+  });
+
+  it('should use correct git range with custom default branch', () => {
+    mockExecFileSync.mockReturnValue('takt: Add search feature\n');
+
+    getOriginalInstruction('/project', 'master', 'takt/20260128-add-search');
+
+    expect(mockExecFileSync).toHaveBeenCalledWith(
+      'git',
+      ['log', '--format=%s', '--reverse', 'master..takt/20260128-add-search'],
+      expect.objectContaining({ cwd: '/project' }),
+    );
+  });
+});

src/__tests__/reviewTasks.test.ts

@@ -93,7 +93,7 @@ describe('extractTaskSlug', () => {
 });
 
 describe('buildReviewItems', () => {
-  it('should build items with correct task slug', () => {
+  it('should build items with correct task slug and originalInstruction', () => {
     const branches: BranchInfo[] = [
       {
         branch: 'takt/20260128-fix-auth',
@@ -107,6 +107,8 @@ describe('buildReviewItems', () => {
     expect(items[0]!.info).toBe(branches[0]);
     // filesChanged will be 0 since we don't have a real git repo
     expect(items[0]!.filesChanged).toBe(0);
+    // originalInstruction will be empty since git command fails on non-existent repo
+    expect(items[0]!.originalInstruction).toBe('');
   });
 
   it('should handle multiple branches', () => {

src/commands/reviewTasks.ts

@@ -78,6 +78,9 @@ async function showDiffAndPromptAction(
 ): Promise<ReviewAction | null> {
   console.log();
   console.log(chalk.bold.cyan(`=== ${item.info.branch} ===`));
+  if (item.originalInstruction) {
+    console.log(chalk.dim(`  ${item.originalInstruction}`));
+  }
   console.log();
 
   // Show diff stat
@@ -353,11 +356,17 @@ export async function reviewTasks(cwd: string): Promise<void> {
     const items = buildReviewItems(cwd, branches, defaultBranch);
 
     // Build selection options
-    const options = items.map((item, idx) => ({
+    const options = items.map((item, idx) => {
+      const filesSummary = `${item.filesChanged} file${item.filesChanged !== 1 ? 's' : ''} changed`;
+      const description = item.originalInstruction
+        ? `${filesSummary} | ${item.originalInstruction}`
+        : filesSummary;
+      return {
         label: item.info.branch,
         value: String(idx),
-      description: `${item.filesChanged} file${item.filesChanged !== 1 ? 's' : ''} changed`,
-    }));
+        description,
+      };
+    });
 
     const selected = await selectOption<string>(
       'Review Tasks (Branches)',

src/task/worktree.ts

@@ -43,13 +43,15 @@ export interface BranchReviewItem {
   info: BranchInfo;
   filesChanged: number;
   taskSlug: string;
+  /** Original task instruction extracted from first commit message */
+  originalInstruction: string;
 }
 
 /**
  * Generate a timestamp string for paths/branches
  */
 function generateTimestamp(): string {
-  return new Date().toISOString().replace(/[:.]/g, '').slice(0, 15);
+  return new Date().toISOString().replace(/[-:.]/g, '').slice(0, 13);
 }
 
 /**
@@ -313,6 +315,41 @@ export function extractTaskSlug(branch: string): string {
   return withoutTimestamp || name;
 }
 
+/**
+ * Extract the original task instruction from the first commit message on a branch.
+ *
+ * The first commit on a takt branch has the format: "takt: {original instruction}".
+ * This function retrieves the first commit's message and strips the "takt: " prefix.
+ * Returns empty string if extraction fails.
+ */
+export function getOriginalInstruction(
+  cwd: string,
+  defaultBranch: string,
+  branch: string,
+): string {
+  try {
+    // Get the first commit message on the branch (oldest first)
+    const output = execFileSync(
+      'git',
+      ['log', '--format=%s', '--reverse', `${defaultBranch}..${branch}`],
+      { cwd, encoding: 'utf-8', stdio: 'pipe' },
+    ).trim();
+
+    if (!output) return '';
+
+    const firstLine = output.split('\n')[0] || '';
+    // Strip "takt: " prefix if present
+    const TAKT_COMMIT_PREFIX = 'takt:';
+    if (firstLine.startsWith(TAKT_COMMIT_PREFIX)) {
+      return firstLine.slice(TAKT_COMMIT_PREFIX.length).trim();
+    }
+
+    return firstLine;
+  } catch {
+    return '';
+  }
+}
+
 /**
  * Build review items from branch list, enriching with diff stats.
  */
@@ -325,5 +362,6 @@ export function buildReviewItems(
     info: br,
     filesChanged: getFilesChanged(projectDir, defaultBranch, br.branch),
     taskSlug: extractTaskSlug(br.branch),
+    originalInstruction: getOriginalInstruction(projectDir, defaultBranch, br.branch),
   }));
 }