diff --git a/src/hooks/useGateway.ts b/src/hooks/useGateway.ts
index fef7308..19f7dfe 100644
--- a/src/hooks/useGateway.ts
+++ b/src/hooks/useGateway.ts
@@ -3,10 +3,10 @@ import { GatewayClient, type JsonPayload } from '../lib/gateway';
 import { genIdempotencyKey } from '../lib/utils';
 import { getStoredCredentials, storeCredentials, clearCredentials, type AuthMode } from '../lib/credentials';
 import { getOrCreateDeviceIdentity } from '../lib/deviceIdentity';
-import { isSystemEvent } from '../lib/systemEvent';
 import { getCachedMessages, setCachedMessages, mergeWithCache } from '../lib/messageCache';
 import { extractAgentIdFromKey } from '../lib/sessionName';
 import { extractText, extractThinking, type ChatPayloadMessage } from '../lib/messageExtract';
+import { parseHistoryMessages } from '../lib/historyParser';
 import type { ChatMessage, MessageBlock, ConnectionStatus, Session, AgentIdentity } from '../types';
 
 export function useGateway() {
@@ -143,80 +143,7 @@ export function useGateway() {
       const res = await clientRef.current?.send('chat.history', { sessionKey, limit: 100 });
       const rawMsgs = res?.messages as Array<Record<string, unknown>> | undefined;
       if (rawMsgs) {
-        /* eslint-disable @typescript-eslint/no-explicit-any -- raw gateway history messages have dynamic shape */
-        const msgs: ChatMessage[] = rawMsgs.map((m: Record<string, any>, i: number) => {
-          const blocks: MessageBlock[] = [];
-          if (m.content) {
-            if (Array.isArray(m.content)) {
-              for (const block of m.content) {
-                if (block.type === 'text') blocks.push({ type: 'text', text: block.text });
-                else if (block.type === 'thinking') blocks.push({ type: 'thinking', text: block.thinking || block.text || '' });
-                else if (block.type === 'image') {
-                  const src = block.source || {};
-                  blocks.push({ type: 'image', mediaType: src.media_type || block.media_type || 'image/png', data: src.data || block.data, url: block.url || src.url });
-                }
-                else if (block.type === 'image_url') {
-                  blocks.push({ type: 'image', mediaType: 'image/png', url: block.image_url?.url || block.url });
-                }
-                else if (block.type === 'tool_use') blocks.push({ type: 'tool_use', name: block.name, input: block.input, id: block.id });
-                else if (block.type === 'tool_result') blocks.push({ type: 'tool_result', content: typeof block.content === 'string' ? block.content : JSON.stringify(block.content, null, 2), toolUseId: block.tool_use_id });
-                else if (block.type === 'toolCall') blocks.push({ type: 'tool_use', name: block.name, input: block.arguments || block.input, id: block.id });
-                else if (block.type === 'toolResult') blocks.push({ type: 'tool_result', content: typeof block.content === 'string' ? block.content : JSON.stringify(block.content, null, 2), toolUseId: block.toolCallId || block.tool_use_id, name: block.name });
-              }
-            } else if (typeof m.content === 'string') {
-              blocks.push({ type: 'text', text: m.content });
-            }
-          }
-          const role: 'user' | 'assistant' = m.role === 'user' ? 'user' : 'assistant';
-
-          if (m.role === 'toolResult') {
-            const toolBlocks: MessageBlock[] = blocks.map(b => {
-              if (b.type === 'text') {
-                return { type: 'tool_result' as const, content: b.text, toolUseId: m.toolCallId };
-              }
-              return b;
-            });
-            return {
-              id: m.id || `hist-${i}`,
-              role: 'assistant' as const,
-              content: '',
-              timestamp: m.timestamp || Date.now(),
-              blocks: toolBlocks,
-              isToolResult: true,
-            };
-          }
-
-          const textContent = blocks.filter((b): b is Extract<MessageBlock, { type: 'text' }> => b.type === 'text').map(b => b.text).join('');
-          // Capture raw metadata (exclude heavy fields already parsed)
-          const metadata: Record<string, unknown> = {};
-          for (const [k, v] of Object.entries(m)) {
-            if (['content', 'blocks'].includes(k)) continue;
-            metadata[k] = v;
-          }
-          return {
-            id: m.id || `hist-${i}`,
-            role,
-            content: textContent,
-            timestamp: m.timestamp || Date.now(),
-            blocks,
-            metadata,
-            isSystemEvent: role === 'user' && isSystemEvent(textContent),
-          };
-        });
-        const merged: ChatMessage[] = [];
-        for (const msg of msgs) {
-          const isToolResult = 'isToolResult' in msg && (msg as ChatMessage & { isToolResult?: boolean }).isToolResult;
-          if (isToolResult && merged.length > 0 && merged[merged.length - 1].role === 'assistant') {
-            merged[merged.length - 1] = {
-              ...merged[merged.length - 1],
-              blocks: [...merged[merged.length - 1].blocks, ...msg.blocks],
-            };
-          } else if (isToolResult) {
-            // skip orphan tool results
-          } else {
-            merged.push(msg);
-          }
-        }
+        const merged = parseHistoryMessages(rawMsgs as Array<Record<string, any>>); // eslint-disable-line @typescript-eslint/no-explicit-any
         // Apply stored generation time to the last assistant message if available
         const genKey = sessionKey + ':latest';
         const genTime = generationTimesRef.current.get(genKey);
diff --git a/src/hooks/useSecondarySession.ts b/src/hooks/useSecondarySession.ts
index 4b6916d..ae3c38a 100644
--- a/src/hooks/useSecondarySession.ts
+++ b/src/hooks/useSecondarySession.ts
@@ -1,7 +1,7 @@
 import { useState, useCallback, useEffect, useRef } from 'react';
 import type { GatewayClient, JsonPayload } from '../lib/gateway';
 import type { ChatMessage, MessageBlock } from '../types';
-import { isSystemEvent } from '../lib/systemEvent';
+import { parseHistoryMessages } from '../lib/historyParser';
 import { extractText, extractThinking } from '../lib/messageExtract';
 import type { ChatPayloadMessage } from '../lib/messageExtract';
 
@@ -28,56 +28,7 @@ export function useSecondarySession(
       const res = await getClient()?.send('chat.history', { sessionKey: key, limit: 100 });
       const rawMsgs = res?.messages as Array<Record<string, unknown>> | undefined;
       if (!rawMsgs) return;
-      /* eslint-disable @typescript-eslint/no-explicit-any */
-      const msgs: ChatMessage[] = rawMsgs.map((m: Record<string, any>, i: number) => {
-        const blocks: MessageBlock[] = [];
-        if (m.content) {
-          if (Array.isArray(m.content)) {
-            for (const block of m.content) {
-              if (block.type === 'text') blocks.push({ type: 'text', text: block.text });
-              else if (block.type === 'thinking') blocks.push({ type: 'thinking', text: block.thinking || block.text || '' });
-              else if (block.type === 'image') {
-                const src = block.source || {};
-                blocks.push({ type: 'image', mediaType: src.media_type || block.media_type || 'image/png', data: src.data || block.data, url: block.url || src.url });
-              }
-              else if (block.type === 'image_url') {
-                blocks.push({ type: 'image', mediaType: 'image/png', url: block.image_url?.url || block.url });
-              }
-              else if (block.type === 'tool_use') blocks.push({ type: 'tool_use', name: block.name, input: block.input, id: block.id });
-              else if (block.type === 'tool_result') blocks.push({ type: 'tool_result', content: typeof block.content === 'string' ? block.content : JSON.stringify(block.content, null, 2), toolUseId: block.tool_use_id });
-              else if (block.type === 'toolCall') blocks.push({ type: 'tool_use', name: block.name, input: block.arguments || block.input, id: block.id });
-              else if (block.type === 'toolResult') blocks.push({ type: 'tool_result', content: typeof block.content === 'string' ? block.content : JSON.stringify(block.content, null, 2), toolUseId: block.toolCallId || block.tool_use_id, name: block.name });
-            }
-          } else if (typeof m.content === 'string') {
-            blocks.push({ type: 'text', text: m.content });
-          }
-        }
-        const role: 'user' | 'assistant' = m.role === 'user' ? 'user' : 'assistant';
-        if (m.role === 'toolResult') {
-          const toolBlocks: MessageBlock[] = blocks.map(b => {
-            if (b.type === 'text') return { type: 'tool_result' as const, content: b.text, toolUseId: m.toolCallId };
-            return b;
-          });
-          return { id: m.id || `hist-${i}`, role: 'assistant' as const, content: '', timestamp: m.timestamp || Date.now(), blocks: toolBlocks, isToolResult: true };
-        }
-        const textContent = blocks.filter((b): b is Extract<MessageBlock, { type: 'text' }> => b.type === 'text').map(b => b.text).join('');
-        const metadata: Record<string, unknown> = {};
-        for (const [k, v] of Object.entries(m)) {
-          if (['content', 'blocks'].includes(k)) continue;
-          metadata[k] = v;
-        }
-        return { id: m.id || `hist-${i}`, role, content: textContent, timestamp: m.timestamp || Date.now(), blocks, metadata, isSystemEvent: role === 'user' && isSystemEvent(textContent) };
-      });
-      /* eslint-enable @typescript-eslint/no-explicit-any */
-      const merged: ChatMessage[] = [];
-      for (const msg of msgs) {
-        const isToolResult = 'isToolResult' in msg && (msg as ChatMessage & { isToolResult?: boolean }).isToolResult;
-        if (isToolResult && merged.length > 0 && merged[merged.length - 1].role === 'assistant') {
-          merged[merged.length - 1] = { ...merged[merged.length - 1], blocks: [...merged[merged.length - 1].blocks, ...msg.blocks] };
-        } else if (!isToolResult) {
-          merged.push(msg);
-        }
-      }
+      const merged = parseHistoryMessages(rawMsgs as Array<Record<string, any>>); // eslint-disable-line @typescript-eslint/no-explicit-any
       setMessages(merged);
     } catch {
       // ignore
diff --git a/src/lib/__tests__/historyParser.test.ts b/src/lib/__tests__/historyParser.test.ts
new file mode 100644
index 0000000..2824db4
--- /dev/null
+++ b/src/lib/__tests__/historyParser.test.ts
@@ -0,0 +1,152 @@
+import { describe, it, expect } from 'vitest';
+import { parseHistoryMessages } from '../historyParser';
+
+describe('parseHistoryMessages', () => {
+  it('returns empty array for empty input', () => {
+    expect(parseHistoryMessages([])).toEqual([]);
+  });
+
+  it('parses a simple text message', () => {
+    const raw = [{ id: '1', role: 'user', content: 'hello', timestamp: 1000 }];
+    const result = parseHistoryMessages(raw);
+    expect(result).toHaveLength(1);
+    expect(result[0].role).toBe('user');
+    expect(result[0].content).toBe('hello');
+    expect(result[0].blocks).toEqual([{ type: 'text', text: 'hello' }]);
+  });
+
+  it('parses array content with text blocks', () => {
+    const raw = [{
+      id: '1', role: 'assistant', timestamp: 1000,
+      content: [{ type: 'text', text: 'hello ' }, { type: 'text', text: 'world' }],
+    }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].content).toBe('hello world');
+    expect(result[0].blocks).toHaveLength(2);
+  });
+
+  it('parses thinking blocks', () => {
+    const raw = [{
+      id: '1', role: 'assistant', timestamp: 1000,
+      content: [{ type: 'thinking', thinking: 'hmm' }, { type: 'text', text: 'answer' }],
+    }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].blocks).toEqual([
+      { type: 'thinking', text: 'hmm' },
+      { type: 'text', text: 'answer' },
+    ]);
+  });
+
+  it('parses image blocks with source object', () => {
+    const raw = [{
+      id: '1', role: 'assistant', timestamp: 1000,
+      content: [{ type: 'image', source: { media_type: 'image/jpeg', data: 'abc' } }],
+    }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].blocks[0]).toEqual({
+      type: 'image', mediaType: 'image/jpeg', data: 'abc', url: undefined,
+    });
+  });
+
+  it('parses image_url blocks', () => {
+    const raw = [{
+      id: '1', role: 'assistant', timestamp: 1000,
+      content: [{ type: 'image_url', image_url: { url: 'https://example.com/img.png' } }],
+    }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].blocks[0]).toEqual({
+      type: 'image', mediaType: 'image/png', url: 'https://example.com/img.png',
+    });
+  });
+
+  it('parses tool_use and tool_result blocks', () => {
+    const raw = [{
+      id: '1', role: 'assistant', timestamp: 1000,
+      content: [
+        { type: 'tool_use', name: 'exec', input: { cmd: 'ls' }, id: 'tc1' },
+        { type: 'tool_result', content: 'file.txt', tool_use_id: 'tc1' },
+      ],
+    }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].blocks).toEqual([
+      { type: 'tool_use', name: 'exec', input: { cmd: 'ls' }, id: 'tc1' },
+      { type: 'tool_result', content: 'file.txt', toolUseId: 'tc1' },
+    ]);
+  });
+
+  it('parses toolCall/toolResult (OpenAI format)', () => {
+    const raw = [{
+      id: '1', role: 'assistant', timestamp: 1000,
+      content: [
+        { type: 'toolCall', name: 'read', arguments: { path: '/tmp' }, id: 'tc2' },
+        { type: 'toolResult', content: 'data', toolCallId: 'tc2', name: 'read' },
+      ],
+    }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].blocks[0]).toEqual({ type: 'tool_use', name: 'read', input: { path: '/tmp' }, id: 'tc2' });
+    expect(result[0].blocks[1]).toEqual({ type: 'tool_result', content: 'data', toolUseId: 'tc2', name: 'read' });
+  });
+
+  it('merges toolResult messages into preceding assistant message', () => {
+    const raw = [
+      { id: '1', role: 'assistant', content: 'thinking...', timestamp: 1000 },
+      { id: '2', role: 'toolResult', content: 'result data', toolCallId: 'tc1', timestamp: 1001 },
+    ];
+    const result = parseHistoryMessages(raw);
+    expect(result).toHaveLength(1);
+    expect(result[0].role).toBe('assistant');
+    expect(result[0].blocks).toHaveLength(2); // text + tool_result
+  });
+
+  it('skips orphan toolResult messages', () => {
+    const raw = [
+      { id: '1', role: 'toolResult', content: 'orphan', toolCallId: 'tc1', timestamp: 1000 },
+      { id: '2', role: 'user', content: 'hello', timestamp: 1001 },
+    ];
+    const result = parseHistoryMessages(raw);
+    expect(result).toHaveLength(1);
+    expect(result[0].role).toBe('user');
+  });
+
+  it('marks user system events', () => {
+    const raw = [{ id: '1', role: 'user', content: '[HEARTBEAT] check', timestamp: 1000 }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].isSystemEvent).toBe(true);
+  });
+
+  it('generates fallback ids when missing', () => {
+    const raw = [{ role: 'user', content: 'no id', timestamp: 1000 }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].id).toBe('hist-0');
+  });
+
+  it('preserves metadata excluding content/blocks', () => {
+    const raw = [{ id: '1', role: 'user', content: 'hi', timestamp: 1000, model: 'gpt-4' }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].metadata?.model).toBe('gpt-4');
+    expect(result[0].metadata?.content).toBeUndefined();
+  });
+
+  it('handles unknown block types gracefully (skips them)', () => {
+    const raw = [{
+      id: '1', role: 'assistant', timestamp: 1000,
+      content: [{ type: 'unknown_type', data: 'foo' }, { type: 'text', text: 'ok' }],
+    }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].blocks).toHaveLength(1);
+    expect(result[0].blocks[0]).toEqual({ type: 'text', text: 'ok' });
+  });
+
+  it('handles tool_result with object content (JSON stringified)', () => {
+    const raw = [{
+      id: '1', role: 'assistant', timestamp: 1000,
+      content: [{ type: 'tool_result', content: { key: 'val' }, tool_use_id: 'tc1' }],
+    }];
+    const result = parseHistoryMessages(raw);
+    expect(result[0].blocks[0]).toEqual({
+      type: 'tool_result',
+      content: JSON.stringify({ key: 'val' }, null, 2),
+      toolUseId: 'tc1',
+    });
+  });
+});
diff --git a/src/lib/historyParser.ts b/src/lib/historyParser.ts
new file mode 100644
index 0000000..a3617ca
--- /dev/null
+++ b/src/lib/historyParser.ts
@@ -0,0 +1,129 @@
+/**
+ * Pure function to parse raw gateway history messages into ChatMessage[].
+ * Shared between useGateway and useSecondarySession to avoid duplication.
+ */
+import type { ChatMessage, MessageBlock } from '../types';
+import { isSystemEvent } from './systemEvent';
+
+/* eslint-disable @typescript-eslint/no-explicit-any -- raw gateway messages have dynamic shape */
+
+/** Parse a single content block from a raw history message. */
+function parseContentBlock(block: Record<string, any>): MessageBlock | null {
+  switch (block.type) {
+    case 'text':
+      return { type: 'text', text: block.text };
+    case 'thinking':
+      return { type: 'thinking', text: block.thinking || block.text || '' };
+    case 'image': {
+      const src = block.source || {};
+      return {
+        type: 'image',
+        mediaType: src.media_type || block.media_type || 'image/png',
+        data: src.data || block.data,
+        url: block.url || src.url,
+      };
+    }
+    case 'image_url':
+      return { type: 'image', mediaType: 'image/png', url: block.image_url?.url || block.url };
+    case 'tool_use':
+      return { type: 'tool_use', name: block.name, input: block.input, id: block.id };
+    case 'tool_result':
+      return {
+        type: 'tool_result',
+        content: typeof block.content === 'string' ? block.content : JSON.stringify(block.content, null, 2),
+        toolUseId: block.tool_use_id,
+      };
+    case 'toolCall':
+      return { type: 'tool_use', name: block.name, input: block.arguments || block.input, id: block.id };
+    case 'toolResult':
+      return {
+        type: 'tool_result',
+        content: typeof block.content === 'string' ? block.content : JSON.stringify(block.content, null, 2),
+        toolUseId: block.toolCallId || block.tool_use_id,
+        name: block.name,
+      };
+    default:
+      return null;
+  }
+}
+
+/** Parse content field (string or array) into MessageBlock[]. */
+function parseContent(content: unknown): MessageBlock[] {
+  if (!content) return [];
+  if (typeof content === 'string') return [{ type: 'text', text: content }];
+  if (Array.isArray(content)) {
+    const blocks: MessageBlock[] = [];
+    for (const block of content) {
+      const parsed = parseContentBlock(block);
+      if (parsed) blocks.push(parsed);
+    }
+    return blocks;
+  }
+  return [];
+}
+
+/**
+ * Parse raw gateway history messages into ChatMessage[].
+ * Merges tool results into their parent assistant messages.
+ */
+export function parseHistoryMessages(rawMsgs: Array<Record<string, any>>): ChatMessage[] {
+  const msgs: (ChatMessage & { isToolResult?: boolean })[] = rawMsgs.map((m, i) => {
+    const blocks = parseContent(m.content);
+    const role: 'user' | 'assistant' = m.role === 'user' ? 'user' : 'assistant';
+
+    if (m.role === 'toolResult') {
+      const toolBlocks: MessageBlock[] = blocks.map(b => {
+        if (b.type === 'text') {
+          return { type: 'tool_result' as const, content: b.text, toolUseId: m.toolCallId };
+        }
+        return b;
+      });
+      return {
+        id: m.id || `hist-${i}`,
+        role: 'assistant' as const,
+        content: '',
+        timestamp: m.timestamp || Date.now(),
+        blocks: toolBlocks,
+        isToolResult: true,
+      };
+    }
+
+    const textContent = blocks
+      .filter((b): b is Extract<MessageBlock, { type: 'text' }> => b.type === 'text')
+      .map(b => b.text)
+      .join('');
+
+    const metadata: Record<string, unknown> = {};
+    for (const [k, v] of Object.entries(m)) {
+      if (['content', 'blocks'].includes(k)) continue;
+      metadata[k] = v;
+    }
+
+    return {
+      id: m.id || `hist-${i}`,
+      role,
+      content: textContent,
+      timestamp: m.timestamp || Date.now(),
+      blocks,
+      metadata,
+      isSystemEvent: role === 'user' && isSystemEvent(textContent),
+    };
+  });
+
+  // Merge tool results into preceding assistant message
+  const merged: ChatMessage[] = [];
+  for (const msg of msgs) {
+    if (msg.isToolResult && merged.length > 0 && merged[merged.length - 1].role === 'assistant') {
+      merged[merged.length - 1] = {
+        ...merged[merged.length - 1],
+        blocks: [...merged[merged.length - 1].blocks, ...msg.blocks],
+      };
+    } else if (!msg.isToolResult) {
+      merged.push(msg);
+    }
+  }
+
+  return merged;
+}
+
+/* eslint-enable @typescript-eslint/no-explicit-any */