diff --git a/src/renderer/components/common/ExportDropdown.tsx b/src/renderer/components/common/ExportDropdown.tsx
new file mode 100644
index 00000000..c35f71d9
--- /dev/null
+++ b/src/renderer/components/common/ExportDropdown.tsx
@@ -0,0 +1,142 @@
+/**
+ * ExportDropdown - Download icon button with dropdown for exporting session data.
+ *
+ * Supports three formats: Markdown (.md), JSON (.json), Plain Text (.txt).
+ * Follows the same close-on-outside-click / Escape patterns as RepositoryDropdown.
+ */
+
+import React, { useCallback, useEffect, useRef, useState } from 'react';
+
+import { triggerDownload } from '@renderer/utils/sessionExporter';
+import { Braces, Download, FileText, Type } from 'lucide-react';
+
+import type { SessionDetail } from '@renderer/types/data';
+import type { ExportFormat } from '@renderer/utils/sessionExporter';
+
+interface ExportDropdownProps {
+  sessionDetail: SessionDetail;
+}
+
+interface FormatOption {
+  format: ExportFormat;
+  label: string;
+  icon: React.ComponentType<{ className?: string }>;
+  ext: string;
+}
+
+const FORMAT_OPTIONS: FormatOption[] = [
+  { format: 'markdown', label: 'Markdown', icon: FileText, ext: '.md' },
+  { format: 'json', label: 'JSON', icon: Braces, ext: '.json' },
+  { format: 'plaintext', label: 'Plain Text', icon: Type, ext: '.txt' },
+];
+
+export const ExportDropdown = ({
+  sessionDetail,
+}: Readonly<ExportDropdownProps>): React.JSX.Element => {
+  const [isOpen, setIsOpen] = useState(false);
+  const [buttonHover, setButtonHover] = useState(false);
+  const [hoveredFormat, setHoveredFormat] = useState<ExportFormat | null>(null);
+  const containerRef = useRef<HTMLDivElement>(null);
+
+  // Close on outside click
+  useEffect(() => {
+    if (!isOpen) return;
+
+    const handleClickOutside = (event: MouseEvent): void => {
+      if (containerRef.current && !containerRef.current.contains(event.target as Node)) {
+        setIsOpen(false);
+      }
+    };
+
+    document.addEventListener('mousedown', handleClickOutside);
+    return () => document.removeEventListener('mousedown', handleClickOutside);
+  }, [isOpen]);
+
+  // Close on Escape
+  useEffect(() => {
+    if (!isOpen) return;
+
+    const handleEscape = (event: KeyboardEvent): void => {
+      if (event.key === 'Escape') {
+        setIsOpen(false);
+      }
+    };
+
+    document.addEventListener('keydown', handleEscape);
+    return () => document.removeEventListener('keydown', handleEscape);
+  }, [isOpen]);
+
+  const handleExport = useCallback(
+    (format: ExportFormat) => {
+      triggerDownload(sessionDetail, format);
+      setIsOpen(false);
+    },
+    [sessionDetail]
+  );
+
+  return (
+    <div ref={containerRef} className="relative">
+      {/* Trigger button */}
+      <button
+        onClick={() => setIsOpen(!isOpen)}
+        onMouseEnter={() => setButtonHover(true)}
+        onMouseLeave={() => setButtonHover(false)}
+        className="rounded-md p-2 transition-colors"
+        style={{
+          color: buttonHover || isOpen ? 'var(--color-text)' : 'var(--color-text-muted)',
+          backgroundColor: buttonHover || isOpen ? 'var(--color-surface-raised)' : 'transparent',
+        }}
+        title="Export session"
+      >
+        <Download className="size-4" />
+      </button>
+
+      {/* Dropdown menu */}
+      {isOpen && (
+        <div
+          className="absolute right-0 top-full z-50 mt-1 w-48 overflow-hidden rounded-md border shadow-lg"
+          style={{
+            backgroundColor: 'var(--color-surface-overlay)',
+            borderColor: 'var(--color-border)',
+          }}
+        >
+          {/* Header */}
+          <div
+            className="px-3 py-2 text-xs font-medium"
+            style={{
+              color: 'var(--color-text-secondary)',
+              borderBottom: '1px solid var(--color-border)',
+            }}
+          >
+            Export Session
+          </div>
+
+          {/* Format options */}
+          {FORMAT_OPTIONS.map((option) => (
+            <button
+              key={option.format}
+              onClick={() => handleExport(option.format)}
+              onMouseEnter={() => setHoveredFormat(option.format)}
+              onMouseLeave={() => setHoveredFormat(null)}
+              className="flex w-full items-center gap-2.5 px-3 py-2 text-left text-xs transition-colors"
+              style={{
+                color:
+                  hoveredFormat === option.format
+                    ? 'var(--color-text)'
+                    : 'var(--color-text-secondary)',
+                backgroundColor:
+                  hoveredFormat === option.format ? 'var(--color-surface-raised)' : 'transparent',
+              }}
+            >
+              <option.icon className="size-3.5" />
+              <span className="flex-1">{option.label}</span>
+              <span className="text-[10px]" style={{ color: 'var(--color-text-muted)' }}>
+                {option.ext}
+              </span>
+            </button>
+          ))}
+        </div>
+      )}
+    </div>
+  );
+};
diff --git a/src/renderer/components/layout/TabBar.tsx b/src/renderer/components/layout/TabBar.tsx
index 6748a0a5..61915d35 100644
--- a/src/renderer/components/layout/TabBar.tsx
+++ b/src/renderer/components/layout/TabBar.tsx
@@ -17,6 +17,8 @@ import { useStore } from '@renderer/store';
 import { Bell, PanelLeft, Plus, RefreshCw, Search, Settings } from 'lucide-react';
 import { useShallow } from 'zustand/react/shallow';
 
+import { ExportDropdown } from '../common/ExportDropdown';
+
 import { SortableTab } from './SortableTab';
 import { TabContextMenu } from './TabContextMenu';
 
@@ -50,6 +52,7 @@ export const TabBar = ({ paneId }: TabBarProps): React.JSX.Element => {
     pinnedSessionIds,
     toggleHideSession,
     hiddenSessionIds,
+    tabSessionData,
   } = useStore(
     useShallow((s) => ({
       pane: s.paneLayout.panes.find((p) => p.id === paneId),
@@ -76,6 +79,7 @@ export const TabBar = ({ paneId }: TabBarProps): React.JSX.Element => {
       pinnedSessionIds: s.pinnedSessionIds,
       toggleHideSession: s.toggleHideSession,
       hiddenSessionIds: s.hiddenSessionIds,
+      tabSessionData: s.tabSessionData,
     }))
   );
 
@@ -89,6 +93,11 @@ export const TabBar = ({ paneId }: TabBarProps): React.JSX.Element => {
   // Derive stable tab IDs array for SortableContext
   const tabIds = useMemo(() => openTabs.map((t) => t.id), [openTabs]);
 
+  // Derive session detail for the active tab (used by export dropdown)
+  const activeTabSessionDetail = activeTabId
+    ? (tabSessionData[activeTabId]?.sessionDetail ?? null)
+    : null;
+
   // Hover states for buttons
   const [expandHover, setExpandHover] = useState(false);
   const [refreshHover, setRefreshHover] = useState(false);
@@ -372,6 +381,11 @@ export const TabBar = ({ paneId }: TabBarProps): React.JSX.Element => {
           <Search className="size-4" />
         </button>
 
+        {/* Export dropdown - show only for session tabs with loaded data */}
+        {activeTab?.type === 'session' && activeTabSessionDetail && (
+          <ExportDropdown sessionDetail={activeTabSessionDetail} />
+        )}
+
         {/* Notifications bell icon */}
         <button
           onClick={openNotificationsTab}
diff --git a/src/renderer/utils/sessionExporter.ts b/src/renderer/utils/sessionExporter.ts
new file mode 100644
index 00000000..ff41340c
--- /dev/null
+++ b/src/renderer/utils/sessionExporter.ts
@@ -0,0 +1,427 @@
+/**
+ * Session export utilities for claude-devtools.
+ *
+ * Provides formatters to export session data as plain text, Markdown, or JSON,
+ * and a download trigger for browser-based file saving.
+ */
+
+import type { Chunk, SessionDetail } from '@renderer/types/data';
+import type { ContentBlock } from '@shared/types';
+
+// =============================================================================
+// Types
+// =============================================================================
+
+export type ExportFormat = 'markdown' | 'json' | 'plaintext';
+
+interface ExtractOptions {
+  includeThinking?: boolean;
+}
+
+// =============================================================================
+// Helpers (not exported)
+// =============================================================================
+
+function formatNumber(n: number): string {
+  return n.toLocaleString('en-US');
+}
+
+function formatCost(cost?: number): string {
+  if (cost == null) return 'N/A';
+  return `$${cost.toFixed(2)}`;
+}
+
+function formatTimestamp(date: Date): string {
+  return date
+    .toISOString()
+    .replace('T', ' ')
+    .replace(/\.\d{3}Z$/, ' UTC');
+}
+
+function formatDurationForExport(ms: number): string {
+  if (ms < 1000) return `${ms}ms`;
+  const secs = Math.floor(ms / 1000);
+  const mins = Math.floor(secs / 60);
+  const remainSecs = secs % 60;
+  if (mins === 0) return `${secs}s`;
+  return `${mins}m ${remainSecs}s`;
+}
+
+function truncate(text: string, maxLen: number): string {
+  if (text.length <= maxLen) return text;
+  return text.slice(0, maxLen) + '...';
+}
+
+// =============================================================================
+// extractTextFromContent
+// =============================================================================
+
+/**
+ * Extract readable text from message content (string or ContentBlock[]).
+ *
+ * @param content - String content or array of ContentBlocks
+ * @param options - Options controlling extraction behavior
+ * @returns Extracted text with newlines between blocks
+ */
+export function extractTextFromContent(
+  content: string | ContentBlock[],
+  options?: ExtractOptions
+): string {
+  if (typeof content === 'string') {
+    return content;
+  }
+
+  if (!Array.isArray(content) || content.length === 0) {
+    return '';
+  }
+
+  const parts: string[] = [];
+
+  for (const block of content) {
+    switch (block.type) {
+      case 'text':
+        parts.push(block.text);
+        break;
+      case 'thinking':
+        if (options?.includeThinking) {
+          parts.push(block.thinking);
+        }
+        break;
+      case 'tool_use':
+        parts.push(`Tool: ${block.name}\nInput: ${JSON.stringify(block.input, null, 2)}`);
+        break;
+      case 'tool_result': {
+        const resultContent = block.content;
+        if (typeof resultContent === 'string') {
+          parts.push(resultContent);
+        } else if (Array.isArray(resultContent)) {
+          // Recursively extract from nested content blocks
+          const nested = extractTextFromContent(resultContent);
+          if (nested) parts.push(nested);
+        }
+        break;
+      }
+      case 'image':
+        parts.push('[Image]');
+        break;
+    }
+  }
+
+  return parts.join('\n');
+}
+
+// =============================================================================
+// Plain Text Chunk Formatters
+// =============================================================================
+
+function formatToolExecutionPlainText(exec: {
+  toolCall: { name: string; input: Record<string, unknown> };
+  result?: { content: string | unknown[]; isError: boolean };
+}): string[] {
+  const lines: string[] = [];
+  lines.push(`  TOOL: ${exec.toolCall.name}`);
+  lines.push(`  Input: ${JSON.stringify(exec.toolCall.input)}`);
+  if (exec.result) {
+    const prefix = exec.result.isError ? '  [ERROR] Result: ' : '  Result: ';
+    const resultText =
+      typeof exec.result.content === 'string'
+        ? exec.result.content
+        : JSON.stringify(exec.result.content);
+    lines.push(`${prefix}${truncate(resultText, 500)}`);
+  } else {
+    lines.push('  [No result]');
+  }
+  return lines;
+}
+
+function formatChunkPlainText(chunk: Chunk): string[] {
+  const lines: string[] = [];
+
+  switch (chunk.chunkType) {
+    case 'user': {
+      lines.push(`USER: ${extractTextFromContent(chunk.userMessage.content)}`);
+      break;
+    }
+    case 'ai': {
+      // Render thinking blocks first, then text
+      for (const response of chunk.responses) {
+        if (Array.isArray(response.content)) {
+          // Check for thinking blocks
+          for (const block of response.content) {
+            if (block.type === 'thinking') {
+              lines.push(`THINKING: ${block.thinking}`);
+            }
+          }
+          // Then text
+          const text = extractTextFromContent(response.content);
+          if (text) {
+            lines.push(`ASSISTANT: ${text}`);
+          }
+        } else if (typeof response.content === 'string') {
+          lines.push(`ASSISTANT: ${response.content}`);
+        }
+      }
+
+      // Tool executions
+      for (const exec of chunk.toolExecutions) {
+        lines.push(...formatToolExecutionPlainText(exec));
+      }
+      break;
+    }
+    case 'system': {
+      lines.push(`SYSTEM: ${chunk.commandOutput}`);
+      break;
+    }
+    case 'compact': {
+      lines.push('[Context compacted]');
+      break;
+    }
+  }
+
+  return lines;
+}
+
+// =============================================================================
+// Markdown Chunk Formatters
+// =============================================================================
+
+function formatToolExecutionMarkdown(exec: {
+  toolCall: { name: string; input: Record<string, unknown> };
+  result?: { content: string | unknown[]; isError: boolean };
+}): string[] {
+  const lines: string[] = [];
+  lines.push(`**Tool:** \`${exec.toolCall.name}\``);
+  lines.push('');
+  lines.push('```json');
+  lines.push(JSON.stringify(exec.toolCall.input, null, 2));
+  lines.push('```');
+  lines.push('');
+
+  if (exec.result) {
+    if (exec.result.isError) {
+      lines.push('**Error:**');
+    } else {
+      lines.push('**Result:**');
+    }
+    lines.push('');
+    const resultText =
+      typeof exec.result.content === 'string'
+        ? exec.result.content
+        : JSON.stringify(exec.result.content, null, 2);
+    lines.push('```');
+    lines.push(truncate(resultText, 2000));
+    lines.push('```');
+  }
+
+  return lines;
+}
+
+function formatChunkMarkdown(chunk: Chunk, turnNum: number): string[] {
+  const lines: string[] = [];
+
+  switch (chunk.chunkType) {
+    case 'user': {
+      lines.push(`### User (Turn ${turnNum})`);
+      lines.push('');
+      lines.push(extractTextFromContent(chunk.userMessage.content));
+      lines.push('');
+      break;
+    }
+    case 'ai': {
+      lines.push(`### Assistant (Turn ${turnNum})`);
+      lines.push('');
+
+      for (const response of chunk.responses) {
+        if (Array.isArray(response.content)) {
+          // Thinking blocks as blockquotes
+          for (const block of response.content) {
+            if (block.type === 'thinking') {
+              lines.push('> *Thinking:*');
+              for (const thinkLine of block.thinking.split('\n')) {
+                lines.push(`> ${thinkLine}`);
+              }
+              lines.push('');
+            }
+          }
+          // Text content
+          const text = extractTextFromContent(response.content);
+          if (text) {
+            lines.push(text);
+            lines.push('');
+          }
+        } else if (typeof response.content === 'string') {
+          lines.push(response.content);
+          lines.push('');
+        }
+      }
+
+      // Tool executions
+      for (const exec of chunk.toolExecutions) {
+        lines.push(...formatToolExecutionMarkdown(exec));
+        lines.push('');
+      }
+      break;
+    }
+    case 'system': {
+      lines.push(`### System (Turn ${turnNum})`);
+      lines.push('');
+      lines.push(chunk.commandOutput);
+      lines.push('');
+      break;
+    }
+    case 'compact': {
+      lines.push('---');
+      lines.push('');
+      lines.push('*Context compacted*');
+      lines.push('');
+      break;
+    }
+  }
+
+  return lines;
+}
+
+// =============================================================================
+// Export Functions
+// =============================================================================
+
+/**
+ * Export session as plain text transcript.
+ *
+ * Produces a flat text format with clear labels (USER:, ASSISTANT:, TOOL:, etc.)
+ * and separator lines between sections.
+ */
+export function exportAsPlainText(detail: SessionDetail): string {
+  const { session, metrics, chunks } = detail;
+  const lines: string[] = [];
+
+  // Header
+  lines.push('═'.repeat(60));
+  lines.push('SESSION EXPORT');
+  lines.push('═'.repeat(60));
+  lines.push(`Session:  ${session.id}`);
+  lines.push(`Project:  ${session.projectPath}`);
+  if (session.gitBranch) {
+    lines.push(`Branch:   ${session.gitBranch}`);
+  }
+  lines.push(`Date:     ${formatTimestamp(new Date(session.createdAt))}`);
+  lines.push('');
+
+  // Metrics
+  lines.push('─'.repeat(40));
+  lines.push('METRICS');
+  lines.push('─'.repeat(40));
+  lines.push(`Duration:       ${formatDurationForExport(metrics.durationMs)}`);
+  lines.push(`Total Tokens:   ${formatNumber(metrics.totalTokens)}`);
+  lines.push(`Input Tokens:   ${formatNumber(metrics.inputTokens)}`);
+  lines.push(`Output Tokens:  ${formatNumber(metrics.outputTokens)}`);
+  lines.push(`Cache Read:     ${formatNumber(metrics.cacheReadTokens)}`);
+  lines.push(`Cache Created:  ${formatNumber(metrics.cacheCreationTokens)}`);
+  lines.push(`Messages:       ${formatNumber(metrics.messageCount)}`);
+  lines.push(`Cost:           ${formatCost(metrics.costUsd)}`);
+  lines.push('');
+
+  // Conversation
+  lines.push('═'.repeat(60));
+  lines.push('CONVERSATION');
+  lines.push('═'.repeat(60));
+  lines.push('');
+
+  for (const chunk of chunks) {
+    lines.push('─'.repeat(40));
+    lines.push(...formatChunkPlainText(chunk));
+    lines.push('');
+  }
+
+  return lines.join('\n');
+}
+
+/**
+ * Export session as structured Markdown.
+ *
+ * Produces Markdown with headings, tables, code blocks, and blockquotes
+ * suitable for viewing in any Markdown renderer.
+ */
+export function exportAsMarkdown(detail: SessionDetail): string {
+  const { session, metrics, chunks } = detail;
+  const lines: string[] = [];
+
+  // Title
+  lines.push('# Session Export');
+  lines.push('');
+
+  // Property table
+  lines.push('| Property | Value |');
+  lines.push('|----------|-------|');
+  lines.push(`| Session | \`${session.id}\` |`);
+  lines.push(`| Project | \`${session.projectPath}\` |`);
+  if (session.gitBranch) {
+    lines.push(`| Branch | \`${session.gitBranch}\` |`);
+  }
+  lines.push(`| Date | ${formatTimestamp(new Date(session.createdAt))} |`);
+  lines.push('');
+
+  // Metrics table
+  lines.push('## Metrics');
+  lines.push('');
+  lines.push('| Metric | Value |');
+  lines.push('|--------|-------|');
+  lines.push(`| Duration | ${formatDurationForExport(metrics.durationMs)} |`);
+  lines.push(`| Total Tokens | ${formatNumber(metrics.totalTokens)} |`);
+  lines.push(`| Input Tokens | ${formatNumber(metrics.inputTokens)} |`);
+  lines.push(`| Output Tokens | ${formatNumber(metrics.outputTokens)} |`);
+  lines.push(`| Cache Read | ${formatNumber(metrics.cacheReadTokens)} |`);
+  lines.push(`| Cache Created | ${formatNumber(metrics.cacheCreationTokens)} |`);
+  lines.push(`| Messages | ${formatNumber(metrics.messageCount)} |`);
+  lines.push(`| Cost | ${formatCost(metrics.costUsd)} |`);
+  lines.push('');
+
+  // Conversation
+  lines.push('## Conversation');
+  lines.push('');
+
+  let turnNum = 0;
+  for (const chunk of chunks) {
+    turnNum++;
+    lines.push(...formatChunkMarkdown(chunk, turnNum));
+  }
+
+  return lines.join('\n');
+}
+
+/**
+ * Export session as pretty-printed JSON.
+ */
+export function exportAsJson(detail: SessionDetail): string {
+  return JSON.stringify(detail, null, 2);
+}
+
+/**
+ * Trigger a browser file download for the given session in the specified format.
+ *
+ * Creates a Blob, generates an object URL, and simulates an anchor click
+ * to initiate the download.
+ */
+export function triggerDownload(detail: SessionDetail, format: ExportFormat): void {
+  const formatters: Record<
+    ExportFormat,
+    { fn: (d: SessionDetail) => string; ext: string; mime: string }
+  > = {
+    markdown: { fn: exportAsMarkdown, ext: 'md', mime: 'text/markdown;charset=utf-8' },
+    json: { fn: exportAsJson, ext: 'json', mime: 'application/json;charset=utf-8' },
+    plaintext: { fn: exportAsPlainText, ext: 'txt', mime: 'text/plain;charset=utf-8' },
+  };
+
+  const { fn, ext, mime } = formatters[format];
+  const content = fn(detail);
+  const blob = new Blob([content], { type: mime });
+  const url = URL.createObjectURL(blob);
+
+  const anchor = document.createElement('a');
+  anchor.href = url;
+  anchor.download = `session-${detail.session.id}.${ext}`;
+  document.body.appendChild(anchor);
+  anchor.click();
+  document.body.removeChild(anchor);
+  URL.revokeObjectURL(url);
+}
diff --git a/test/renderer/utils/sessionExporter.test.ts b/test/renderer/utils/sessionExporter.test.ts
new file mode 100644
index 00000000..c0bd4a57
--- /dev/null
+++ b/test/renderer/utils/sessionExporter.test.ts
@@ -0,0 +1,716 @@
+import { describe, expect, it, vi, beforeEach } from 'vitest';
+
+import {
+  extractTextFromContent,
+  exportAsPlainText,
+  exportAsMarkdown,
+  exportAsJson,
+  triggerDownload,
+  type ExportFormat,
+} from '@renderer/utils/sessionExporter';
+
+// =============================================================================
+// Test Fixtures
+// =============================================================================
+
+function makeMetrics(overrides = {}) {
+  return {
+    durationMs: 60000,
+    totalTokens: 5000,
+    inputTokens: 3000,
+    outputTokens: 2000,
+    cacheReadTokens: 500,
+    cacheCreationTokens: 100,
+    messageCount: 10,
+    costUsd: 0.05,
+    ...overrides,
+  };
+}
+
+function makeSession(overrides = {}) {
+  return {
+    id: 'test-session-123',
+    projectId: '-Users-test-project',
+    projectPath: '/Users/test/project',
+    createdAt: new Date('2025-01-15T10:00:00Z').getTime(),
+    hasSubagents: false,
+    messageCount: 10,
+    firstMessage: 'Hello, help me debug this',
+    gitBranch: 'main',
+    ...overrides,
+  };
+}
+
+function makeMessage(overrides: Record<string, unknown> = {}) {
+  return {
+    uuid: 'msg-1',
+    parentUuid: null,
+    type: 'user' as const,
+    timestamp: new Date('2025-01-15T10:00:00Z'),
+    content: 'Hello world',
+    isMeta: false,
+    isSidechain: false,
+    toolCalls: [],
+    toolResults: [],
+    ...overrides,
+  };
+}
+
+function makeUserChunk(overrides: Record<string, unknown> = {}) {
+  const msg = makeMessage();
+  return {
+    id: 'chunk-user-1',
+    chunkType: 'user' as const,
+    startTime: new Date('2025-01-15T10:00:00Z'),
+    endTime: new Date('2025-01-15T10:00:01Z'),
+    durationMs: 1000,
+    metrics: makeMetrics({ messageCount: 1 }),
+    userMessage: msg,
+    ...overrides,
+  };
+}
+
+function makeAIChunk(overrides: Record<string, unknown> = {}) {
+  const response = makeMessage({
+    uuid: 'msg-2',
+    type: 'assistant',
+    content: [{ type: 'text', text: 'Here is the answer' }],
+  });
+  return {
+    id: 'chunk-ai-1',
+    chunkType: 'ai' as const,
+    startTime: new Date('2025-01-15T10:00:01Z'),
+    endTime: new Date('2025-01-15T10:00:05Z'),
+    durationMs: 4000,
+    metrics: makeMetrics({ messageCount: 2 }),
+    responses: [response],
+    processes: [],
+    sidechainMessages: [],
+    toolExecutions: [],
+    ...overrides,
+  };
+}
+
+function makeSystemChunk(overrides: Record<string, unknown> = {}) {
+  return {
+    id: 'chunk-system-1',
+    chunkType: 'system' as const,
+    startTime: new Date('2025-01-15T10:00:06Z'),
+    endTime: new Date('2025-01-15T10:00:07Z'),
+    durationMs: 1000,
+    metrics: makeMetrics({ messageCount: 1 }),
+    message: makeMessage({ type: 'user', content: 'command output here' }),
+    commandOutput: 'Set model to sonnet',
+    ...overrides,
+  };
+}
+
+function makeCompactChunk(overrides: Record<string, unknown> = {}) {
+  return {
+    id: 'chunk-compact-1',
+    chunkType: 'compact' as const,
+    startTime: new Date('2025-01-15T10:01:00Z'),
+    endTime: new Date('2025-01-15T10:01:00Z'),
+    durationMs: 0,
+    metrics: makeMetrics({ messageCount: 0 }),
+    message: makeMessage({ type: 'summary', content: 'Summary of conversation' }),
+    ...overrides,
+  };
+}
+
+function makeSessionDetail(overrides: Record<string, unknown> = {}) {
+  const userChunk = makeUserChunk();
+  const aiChunk = makeAIChunk();
+  return {
+    session: makeSession(),
+    messages: [userChunk.userMessage as any, (aiChunk.responses as any)[0]],
+    chunks: [userChunk, aiChunk],
+    processes: [],
+    metrics: makeMetrics(),
+    ...overrides,
+  };
+}
+
+// =============================================================================
+// extractTextFromContent
+// =============================================================================
+
+describe('extractTextFromContent', () => {
+  it('returns string content directly', () => {
+    expect(extractTextFromContent('Hello world')).toBe('Hello world');
+  });
+
+  it('returns empty string for empty string', () => {
+    expect(extractTextFromContent('')).toBe('');
+  });
+
+  it('extracts text from TextContent blocks', () => {
+    const blocks = [
+      { type: 'text', text: 'First part.' },
+      { type: 'text', text: 'Second part.' },
+    ];
+    expect(extractTextFromContent(blocks as any)).toBe('First part.\nSecond part.');
+  });
+
+  it('includes thinking content when option is set', () => {
+    const blocks = [
+      { type: 'thinking', thinking: 'Let me think about this...' },
+      { type: 'text', text: 'Answer here.' },
+    ];
+    expect(extractTextFromContent(blocks as any, { includeThinking: true })).toBe(
+      'Let me think about this...\nAnswer here.'
+    );
+  });
+
+  it('excludes thinking content by default', () => {
+    const blocks = [
+      { type: 'thinking', thinking: 'Let me think...' },
+      { type: 'text', text: 'Answer here.' },
+    ];
+    expect(extractTextFromContent(blocks as any)).toBe('Answer here.');
+  });
+
+  it('extracts tool_use content as formatted string', () => {
+    const blocks = [{ type: 'tool_use', id: 'tu-1', name: 'Read', input: { path: '/foo.ts' } }];
+    const result = extractTextFromContent(blocks as any);
+    expect(result).toContain('Tool: Read');
+    expect(result).toContain('/foo.ts');
+  });
+
+  it('extracts tool_result content', () => {
+    const blocks = [{ type: 'tool_result', tool_use_id: 'tu-1', content: 'file contents here' }];
+    const result = extractTextFromContent(blocks as any);
+    expect(result).toContain('file contents here');
+  });
+
+  it('handles tool_result with array content', () => {
+    const blocks = [
+      {
+        type: 'tool_result',
+        tool_use_id: 'tu-1',
+        content: [{ type: 'text', text: 'result text' }],
+      },
+    ];
+    const result = extractTextFromContent(blocks as any);
+    expect(result).toContain('result text');
+  });
+
+  it('skips image blocks gracefully', () => {
+    const blocks = [
+      { type: 'image', source: { type: 'base64', media_type: 'image/png', data: '...' } },
+      { type: 'text', text: 'Caption' },
+    ];
+    expect(extractTextFromContent(blocks as any)).toBe('[Image]\nCaption');
+  });
+
+  it('returns empty string for empty array', () => {
+    expect(extractTextFromContent([])).toBe('');
+  });
+});
+
+// =============================================================================
+// exportAsPlainText
+// =============================================================================
+
+describe('exportAsPlainText', () => {
+  it('includes session header with metadata', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('SESSION EXPORT');
+    expect(result).toContain('test-session-123');
+    expect(result).toContain('/Users/test/project');
+  });
+
+  it('includes metrics section', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('METRICS');
+    expect(result).toContain('5,000');
+    expect(result).toContain('$0.05');
+  });
+
+  it('renders user chunks with USER: label', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('USER:');
+    expect(result).toContain('Hello world');
+  });
+
+  it('renders AI chunks with ASSISTANT: label', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('ASSISTANT:');
+    expect(result).toContain('Here is the answer');
+  });
+
+  it('renders system chunks with SYSTEM: label', () => {
+    const detail = makeSessionDetail({
+      chunks: [makeSystemChunk()],
+    });
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('SYSTEM:');
+    expect(result).toContain('Set model to sonnet');
+  });
+
+  it('renders compact chunks as [Context compacted]', () => {
+    const detail = makeSessionDetail({
+      chunks: [makeCompactChunk()],
+    });
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('[Context compacted]');
+  });
+
+  it('renders tool executions with TOOL: label', () => {
+    const aiChunk = makeAIChunk({
+      toolExecutions: [
+        {
+          toolCall: {
+            id: 'tu-1',
+            name: 'Read',
+            input: { file_path: '/src/main.ts' },
+            isTask: false,
+          },
+          result: { toolUseId: 'tu-1', content: 'file content', isError: false },
+          startTime: new Date('2025-01-15T10:00:02Z'),
+          endTime: new Date('2025-01-15T10:00:03Z'),
+          durationMs: 1000,
+        },
+      ],
+    });
+    const detail = makeSessionDetail({ chunks: [makeUserChunk(), aiChunk] });
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('TOOL: Read');
+    expect(result).toContain('/src/main.ts');
+    expect(result).toContain('file content');
+  });
+
+  it('renders thinking blocks with THINKING: label', () => {
+    const aiChunk = makeAIChunk({
+      responses: [
+        makeMessage({
+          uuid: 'msg-think',
+          type: 'assistant',
+          content: [
+            { type: 'thinking', thinking: 'Let me reason about this...' },
+            { type: 'text', text: 'Final answer.' },
+          ],
+        }),
+      ],
+    });
+    const detail = makeSessionDetail({ chunks: [makeUserChunk(), aiChunk] });
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('THINKING:');
+    expect(result).toContain('Let me reason about this...');
+    expect(result).toContain('Final answer.');
+  });
+
+  it('handles tool execution with error result', () => {
+    const aiChunk = makeAIChunk({
+      toolExecutions: [
+        {
+          toolCall: { id: 'tu-1', name: 'Bash', input: { command: 'rm -rf /' }, isTask: false },
+          result: { toolUseId: 'tu-1', content: 'Permission denied', isError: true },
+          startTime: new Date('2025-01-15T10:00:02Z'),
+        },
+      ],
+    });
+    const detail = makeSessionDetail({ chunks: [makeUserChunk(), aiChunk] });
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('TOOL: Bash');
+    expect(result).toContain('[ERROR]');
+    expect(result).toContain('Permission denied');
+  });
+
+  it('uses separator lines between chunks', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsPlainText(detail as any);
+
+    // Should contain horizontal rule separators
+    expect(result).toMatch(/─{20,}/);
+  });
+
+  it('formats cost as N/A when undefined', () => {
+    const detail = makeSessionDetail({
+      metrics: makeMetrics({ costUsd: undefined }),
+    });
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('N/A');
+  });
+
+  it('includes branch info when available', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsPlainText(detail as any);
+
+    expect(result).toContain('main');
+  });
+});
+
+// =============================================================================
+// exportAsMarkdown
+// =============================================================================
+
+describe('exportAsMarkdown', () => {
+  it('starts with # Session Export heading', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toMatch(/^# Session Export/);
+  });
+
+  it('includes property table with session info', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('| Property | Value |');
+    expect(result).toContain('test-session-123');
+    expect(result).toContain('/Users/test/project');
+    expect(result).toContain('main');
+  });
+
+  it('includes ## Metrics table', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('## Metrics');
+    expect(result).toContain('| Metric | Value |');
+    expect(result).toContain('5,000');
+    expect(result).toContain('$0.05');
+  });
+
+  it('includes ## Conversation section', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('## Conversation');
+  });
+
+  it('renders user chunks with ### User heading', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('### User');
+    expect(result).toContain('Hello world');
+  });
+
+  it('renders AI chunks with ### Assistant heading', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('### Assistant');
+    expect(result).toContain('Here is the answer');
+  });
+
+  it('renders system chunks with ### System heading', () => {
+    const detail = makeSessionDetail({
+      chunks: [makeSystemChunk()],
+    });
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('### System');
+    expect(result).toContain('Set model to sonnet');
+  });
+
+  it('renders compact chunks with --- and italic text', () => {
+    const detail = makeSessionDetail({
+      chunks: [makeCompactChunk()],
+    });
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('---');
+    expect(result).toContain('*Context compacted*');
+  });
+
+  it('renders tool calls with **Tool:** and code blocks', () => {
+    const aiChunk = makeAIChunk({
+      toolExecutions: [
+        {
+          toolCall: {
+            id: 'tu-1',
+            name: 'Read',
+            input: { file_path: '/src/app.ts' },
+            isTask: false,
+          },
+          result: { toolUseId: 'tu-1', content: 'export default App;', isError: false },
+          startTime: new Date('2025-01-15T10:00:02Z'),
+        },
+      ],
+    });
+    const detail = makeSessionDetail({ chunks: [makeUserChunk(), aiChunk] });
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('**Tool:** `Read`');
+    expect(result).toContain('```json');
+    expect(result).toContain('file_path');
+    expect(result).toContain('```');
+    expect(result).toContain('export default App;');
+  });
+
+  it('renders thinking as blockquotes', () => {
+    const aiChunk = makeAIChunk({
+      responses: [
+        makeMessage({
+          uuid: 'msg-think',
+          type: 'assistant',
+          content: [
+            { type: 'thinking', thinking: 'Deep thought here' },
+            { type: 'text', text: 'Output text' },
+          ],
+        }),
+      ],
+    });
+    const detail = makeSessionDetail({ chunks: [makeUserChunk(), aiChunk] });
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('> *Thinking:*');
+    expect(result).toContain('> Deep thought here');
+  });
+
+  it('marks error tool results', () => {
+    const aiChunk = makeAIChunk({
+      toolExecutions: [
+        {
+          toolCall: { id: 'tu-1', name: 'Bash', input: { command: 'fail' }, isTask: false },
+          result: { toolUseId: 'tu-1', content: 'Error: not found', isError: true },
+          startTime: new Date('2025-01-15T10:00:02Z'),
+        },
+      ],
+    });
+    const detail = makeSessionDetail({ chunks: [makeUserChunk(), aiChunk] });
+    const result = exportAsMarkdown(detail as any);
+
+    expect(result).toContain('**Error:**');
+  });
+
+  it('numbers turns sequentially', () => {
+    const detail = makeSessionDetail({
+      chunks: [
+        makeUserChunk(),
+        makeAIChunk(),
+        makeUserChunk({ id: 'chunk-user-2' }),
+        makeAIChunk({ id: 'chunk-ai-2' }),
+      ],
+    });
+    const result = exportAsMarkdown(detail as any);
+
+    // Check that turn numbers appear (Turn 1, Turn 2, etc.)
+    const turnMatches = result.match(/### (User|Assistant)/g);
+    expect(turnMatches).toBeTruthy();
+    expect(turnMatches!.length).toBeGreaterThanOrEqual(2);
+  });
+});
+
+// =============================================================================
+// exportAsJson
+// =============================================================================
+
+describe('exportAsJson', () => {
+  it('returns valid JSON', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsJson(detail as any);
+
+    expect(() => JSON.parse(result)).not.toThrow();
+  });
+
+  it('returns pretty-printed JSON with 2-space indentation', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsJson(detail as any);
+
+    // Pretty-printed JSON has newlines and indentation
+    expect(result).toContain('\n');
+    expect(result).toContain('  ');
+  });
+
+  it('preserves session data', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsJson(detail as any);
+    const parsed = JSON.parse(result);
+
+    expect(parsed.session.id).toBe('test-session-123');
+    expect(parsed.session.projectPath).toBe('/Users/test/project');
+  });
+
+  it('preserves metrics', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsJson(detail as any);
+    const parsed = JSON.parse(result);
+
+    expect(parsed.metrics.totalTokens).toBe(5000);
+    expect(parsed.metrics.costUsd).toBe(0.05);
+  });
+
+  it('preserves chunks array', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsJson(detail as any);
+    const parsed = JSON.parse(result);
+
+    expect(parsed.chunks).toBeDefined();
+    expect(Array.isArray(parsed.chunks)).toBe(true);
+    expect(parsed.chunks.length).toBe(2);
+  });
+
+  it('preserves messages array', () => {
+    const detail = makeSessionDetail();
+    const result = exportAsJson(detail as any);
+    const parsed = JSON.parse(result);
+
+    expect(parsed.messages).toBeDefined();
+    expect(Array.isArray(parsed.messages)).toBe(true);
+  });
+});
+
+// =============================================================================
+// triggerDownload
+// =============================================================================
+
+describe('triggerDownload', () => {
+  let createElementSpy: ReturnType<typeof vi.spyOn>;
+  let mockAnchor: { href: string; download: string; click: ReturnType<typeof vi.fn> };
+
+  beforeEach(() => {
+    mockAnchor = {
+      href: '',
+      download: '',
+      click: vi.fn(),
+    };
+    createElementSpy = vi.spyOn(document, 'createElement').mockReturnValue(mockAnchor as any);
+    vi.spyOn(document.body, 'appendChild').mockReturnValue(mockAnchor as any);
+    vi.spyOn(document.body, 'removeChild').mockReturnValue(mockAnchor as any);
+    vi.spyOn(URL, 'createObjectURL').mockReturnValue('blob:mock-url');
+    vi.spyOn(URL, 'revokeObjectURL').mockImplementation(() => {});
+  });
+
+  it('creates anchor element and triggers click for markdown', () => {
+    const detail = makeSessionDetail();
+    triggerDownload(detail as any, 'markdown');
+
+    expect(createElementSpy).toHaveBeenCalledWith('a');
+    expect(mockAnchor.download).toBe('session-test-session-123.md');
+    expect(mockAnchor.click).toHaveBeenCalled();
+  });
+
+  it('uses .json extension for json format', () => {
+    const detail = makeSessionDetail();
+    triggerDownload(detail as any, 'json');
+
+    expect(mockAnchor.download).toBe('session-test-session-123.json');
+  });
+
+  it('uses .txt extension for plaintext format', () => {
+    const detail = makeSessionDetail();
+    triggerDownload(detail as any, 'plaintext');
+
+    expect(mockAnchor.download).toBe('session-test-session-123.txt');
+  });
+
+  it('creates and revokes object URL', () => {
+    const detail = makeSessionDetail();
+    triggerDownload(detail as any, 'markdown');
+
+    expect(URL.createObjectURL).toHaveBeenCalled();
+    expect(URL.revokeObjectURL).toHaveBeenCalledWith('blob:mock-url');
+  });
+
+  it('appends and removes anchor from body', () => {
+    const detail = makeSessionDetail();
+    triggerDownload(detail as any, 'plaintext');
+
+    expect(document.body.appendChild).toHaveBeenCalled();
+    expect(document.body.removeChild).toHaveBeenCalled();
+  });
+});
+
+// =============================================================================
+// Edge cases
+// =============================================================================
+
+describe('edge cases', () => {
+  it('handles empty chunks array', () => {
+    const detail = makeSessionDetail({ chunks: [], messages: [] });
+
+    expect(() => exportAsPlainText(detail as any)).not.toThrow();
+    expect(() => exportAsMarkdown(detail as any)).not.toThrow();
+    expect(() => exportAsJson(detail as any)).not.toThrow();
+  });
+
+  it('handles AI chunk with no tool executions', () => {
+    const aiChunk = makeAIChunk({ toolExecutions: [] });
+    const detail = makeSessionDetail({ chunks: [makeUserChunk(), aiChunk] });
+
+    const text = exportAsPlainText(detail as any);
+    expect(text).toContain('ASSISTANT:');
+    expect(text).not.toContain('TOOL:');
+  });
+
+  it('handles AI chunk with no responses', () => {
+    const aiChunk = makeAIChunk({ responses: [] });
+    const detail = makeSessionDetail({ chunks: [aiChunk] });
+
+    expect(() => exportAsPlainText(detail as any)).not.toThrow();
+    expect(() => exportAsMarkdown(detail as any)).not.toThrow();
+  });
+
+  it('handles tool execution without result', () => {
+    const aiChunk = makeAIChunk({
+      toolExecutions: [
+        {
+          toolCall: { id: 'tu-1', name: 'Bash', input: { command: 'ls' }, isTask: false },
+          startTime: new Date('2025-01-15T10:00:02Z'),
+        },
+      ],
+    });
+    const detail = makeSessionDetail({ chunks: [makeUserChunk(), aiChunk] });
+
+    const text = exportAsPlainText(detail as any);
+    expect(text).toContain('TOOL: Bash');
+    expect(text).toContain('[No result]');
+  });
+
+  it('handles mixed chunk types in sequence', () => {
+    const detail = makeSessionDetail({
+      chunks: [
+        makeUserChunk(),
+        makeAIChunk(),
+        makeSystemChunk(),
+        makeCompactChunk(),
+        makeUserChunk({ id: 'chunk-user-2' }),
+        makeAIChunk({ id: 'chunk-ai-2' }),
+      ],
+    });
+
+    const text = exportAsPlainText(detail as any);
+    expect(text).toContain('USER:');
+    expect(text).toContain('ASSISTANT:');
+    expect(text).toContain('SYSTEM:');
+    expect(text).toContain('[Context compacted]');
+
+    const md = exportAsMarkdown(detail as any);
+    expect(md).toContain('### User');
+    expect(md).toContain('### Assistant');
+    expect(md).toContain('### System');
+    expect(md).toContain('*Context compacted*');
+  });
+
+  it('handles content blocks with mixed types', () => {
+    const blocks = [
+      { type: 'thinking', thinking: 'Hmm...' },
+      { type: 'tool_use', id: 'tu-1', name: 'Read', input: { path: '/a.ts' } },
+      { type: 'text', text: 'Result text' },
+      { type: 'tool_result', tool_use_id: 'tu-1', content: 'file data' },
+    ];
+    const result = extractTextFromContent(blocks as any, { includeThinking: true });
+    expect(result).toContain('Hmm...');
+    expect(result).toContain('Tool: Read');
+    expect(result).toContain('Result text');
+    expect(result).toContain('file data');
+  });
+});