fix: normalize message roles for local model backends (llama.cpp, Ollama)

Local backends using strict chat templates (e.g. Mistral 3) rejected
Flynn's Anthropic-style tool_use/tool_result content blocks, causing
'roles must alternate' errors. Added getMessageTextWithTools() and
normalizeMessagesForLocal() to serialize structured blocks to plain
text, drop empty messages, and merge consecutive same-role messages.
Also fixed compaction to ensure kept messages start with user role.

src/models/media.test.ts

@@ -8,6 +8,8 @@ import {
   attachmentToImageSource,
   buildUserMessage,
   getMessageText,
+  getMessageTextWithTools,
+  normalizeMessagesForLocal,
   hasImages,
   transcribeAudio,
   buildUserMessageWithAudio,
@@ -605,3 +607,216 @@ describe('buildUserMessageWithAudio', () => {
     expect(result.content).toContain('[Voice message]:');
   });
 });
+
+// ---------------------------------------------------------------------------
+// 10. getMessageTextWithTools
+// ---------------------------------------------------------------------------
+
+describe('getMessageTextWithTools', () => {
+  it('returns string directly for string content', () => {
+    const msg: Message = { role: 'user', content: 'plain text' };
+    expect(getMessageTextWithTools(msg)).toBe('plain text');
+  });
+
+  it('extracts text from text-only array content', () => {
+    const msg: Message = {
+      role: 'assistant',
+      content: [
+        { type: 'text', text: 'Hello ' },
+        { type: 'text', text: 'World' },
+      ],
+    };
+    expect(getMessageTextWithTools(msg)).toBe('Hello \nWorld');
+  });
+
+  it('serializes tool_use blocks to readable text', () => {
+    const msg = {
+      role: 'assistant',
+      content: [
+        { type: 'tool_use', name: 'search', input: { query: 'foo' } },
+      ],
+    } as unknown as Message;
+
+    expect(getMessageTextWithTools(msg)).toBe('[Calling tool: search({"query":"foo"})]');
+  });
+
+  it('serializes tool_result blocks to readable text', () => {
+    const msg = {
+      role: 'user',
+      content: [
+        { type: 'tool_result', content: 'Found 3 results' },
+      ],
+    } as unknown as Message;
+
+    expect(getMessageTextWithTools(msg)).toBe('[Tool result: Found 3 results]');
+  });
+
+  it('marks error tool_result blocks', () => {
+    const msg = {
+      role: 'user',
+      content: [
+        { type: 'tool_result', content: 'File not found', is_error: true },
+      ],
+    } as unknown as Message;
+
+    expect(getMessageTextWithTools(msg)).toBe('[Tool result (error): File not found]');
+  });
+
+  it('handles mixed content (text + tool_use + tool_result) joined with newline', () => {
+    const msg = {
+      role: 'assistant',
+      content: [
+        { type: 'text', text: 'Let me search for that.' },
+        { type: 'tool_use', name: 'web_search', input: { q: 'test' } },
+        { type: 'tool_result', content: 'No results' },
+      ],
+    } as unknown as Message;
+
+    const result = getMessageTextWithTools(msg);
+    expect(result).toBe(
+      'Let me search for that.\n[Calling tool: web_search({"q":"test"})]\n[Tool result: No results]',
+    );
+  });
+
+  it('returns empty string for empty array content', () => {
+    const msg: Message = {
+      role: 'assistant',
+      content: [],
+    };
+    expect(getMessageTextWithTools(msg)).toBe('');
+  });
+});
+
+// ---------------------------------------------------------------------------
+// 11. normalizeMessagesForLocal
+// ---------------------------------------------------------------------------
+
+describe('normalizeMessagesForLocal', () => {
+  it('passes through simple text messages', () => {
+    const messages: Message[] = [
+      { role: 'user', content: 'Hello' },
+      { role: 'assistant', content: 'Hi there' },
+    ];
+
+    const result = normalizeMessagesForLocal(undefined, messages);
+
+    expect(result).toEqual([
+      { role: 'user', content: 'Hello' },
+      { role: 'assistant', content: 'Hi there' },
+    ]);
+  });
+
+  it('prepends system message when provided', () => {
+    const messages: Message[] = [
+      { role: 'user', content: 'Hello' },
+    ];
+
+    const result = normalizeMessagesForLocal('You are helpful.', messages);
+
+    expect(result).toEqual([
+      { role: 'system', content: 'You are helpful.' },
+      { role: 'user', content: 'Hello' },
+    ]);
+  });
+
+  it('omits system message when undefined', () => {
+    const messages: Message[] = [
+      { role: 'user', content: 'Hello' },
+    ];
+
+    const result = normalizeMessagesForLocal(undefined, messages);
+
+    expect(result).toEqual([
+      { role: 'user', content: 'Hello' },
+    ]);
+  });
+
+  it('merges consecutive same-role messages', () => {
+    const messages: Message[] = [
+      { role: 'user', content: 'Part 1' },
+      { role: 'user', content: 'Part 2' },
+      { role: 'assistant', content: 'Response' },
+    ];
+
+    const result = normalizeMessagesForLocal(undefined, messages);
+
+    expect(result).toEqual([
+      { role: 'user', content: 'Part 1\n\nPart 2' },
+      { role: 'assistant', content: 'Response' },
+    ]);
+  });
+
+  it('drops empty messages (e.g. image-only content that serializes to "")', () => {
+    const messages: Message[] = [
+      { role: 'user', content: 'Before' },
+      {
+        role: 'user',
+        content: [
+          { type: 'image', source: { type: 'url', media_type: 'image/png', url: 'https://example.com/img.png' } },
+        ],
+      },
+      { role: 'assistant', content: 'After' },
+    ];
+
+    const result = normalizeMessagesForLocal(undefined, messages);
+
+    expect(result).toEqual([
+      { role: 'user', content: 'Before' },
+      { role: 'assistant', content: 'After' },
+    ]);
+  });
+
+  it('handles realistic agent tool loop sequence', () => {
+    // Simulates: user asks question → assistant calls tool → user provides result → assistant responds
+    const messages = [
+      { role: 'user', content: 'What is the weather?' },
+      {
+        role: 'assistant',
+        content: [
+          { type: 'text', text: 'Let me check.' },
+          { type: 'tool_use', name: 'get_weather', input: { city: 'London' } },
+        ],
+      },
+      {
+        role: 'user',
+        content: [
+          { type: 'tool_result', content: 'Sunny, 22°C' },
+        ],
+      },
+      { role: 'assistant', content: 'The weather in London is sunny at 22°C.' },
+    ] as unknown as Message[];
+
+    const result = normalizeMessagesForLocal('You are a weather bot.', messages);
+
+    expect(result).toEqual([
+      { role: 'system', content: 'You are a weather bot.' },
+      { role: 'user', content: 'What is the weather?' },
+      { role: 'assistant', content: 'Let me check.\n[Calling tool: get_weather({"city":"London"})]' },
+      { role: 'user', content: '[Tool result: Sunny, 22°C]' },
+      { role: 'assistant', content: 'The weather in London is sunny at 22°C.' },
+    ]);
+  });
+
+  it('returns empty array when all messages are empty', () => {
+    const messages: Message[] = [
+      { role: 'user', content: '' },
+      { role: 'assistant', content: '' },
+    ];
+
+    const result = normalizeMessagesForLocal(undefined, messages);
+
+    expect(result).toEqual([]);
+  });
+
+  it('returns only system message when all messages are empty but system is set', () => {
+    const messages: Message[] = [
+      { role: 'user', content: '' },
+    ];
+
+    const result = normalizeMessagesForLocal('System prompt', messages);
+
+    expect(result).toEqual([
+      { role: 'system', content: 'System prompt' },
+    ]);
+  });
+});