feat(utils): implement static and dynamic system prompt

| File | Description |
| --- | --- |
| src/constants/prompt.ts | Static base system prompt with coding assistant persona and tool instructions |
| src/utils/agents.ts | Dynamic loader that combines base prompt with AGENTS.md content (if present) |
| src/components/Chat.tsx | Initializes messages state with system message |
| src/utils/agents.test.ts | Tests for system prompt building |

Features:
- Base prompt uses TUI-style imperative instructions ("You are
  a coding assistant... Always use tools...")
- Dynamically loads `AGENTS.md` from current working directory at startup
- Combines both into a single system message as the first message in
  every conversation
- Gracefully handles missing `AGENTS.md` or file read errors

Author: remarkablemark

src/components/Chat.test.tsx

@@ -14,24 +14,23 @@ const mockState = vi.hoisted(() => ({
   },
 }));
 
-vi.mock('./Messages', () => ({
-  Messages: ({
-    messages,
-    isLoading,
-  }: {
-    messages: { role: string; content: string }[];
-    isLoading: boolean;
-  }) => (
-    <>
-      {messages.map((m, i) => (
-        <Text key={i}>{m.content}</Text>
-      ))}
-      {isLoading && messages[messages.length - 1]?.content === '' && (
-        <Text>⏳Thinking...</Text>
-      )}
-    </>
-  ),
-}));
+vi.mock('../utils', async () => {
+  const actual = await vi.importActual<typeof import('../utils')>('../utils');
+  return {
+    ...actual,
+    ollama: {
+      streamChat: vi.fn().mockImplementation(function* () {
+        yield { type: 'content', content: 'Mocked' };
+        yield { type: 'content', content: ' response' };
+      }),
+    },
+    tools: {
+      TOOLS: [],
+      TOOLS_REQUIRING_APPROVAL: new Set(),
+      executeTool: vi.fn(),
+    },
+  };
+});
 
 vi.mock('./Autocomplete', () => ({
   Autocomplete: (props: {
@@ -61,20 +60,6 @@ vi.mock('./Autocomplete', () => ({
 
 import { Chat } from './Chat';
 
-vi.mock('../utils', () => ({
-  ollama: {
-    streamChat: vi.fn().mockImplementation(function* () {
-      yield { type: 'content', content: 'Mocked' };
-      yield { type: 'content', content: ' response' };
-    }),
-  },
-  tools: {
-    TOOLS: [],
-    TOOLS_REQUIRING_APPROVAL: new Set(),
-    executeTool: vi.fn(),
-  },
-}));
-
 async function typeText(
   rerender: (tree: React.ReactElement) => void,
   text: string,
@@ -102,61 +87,74 @@ describe('Chat', () => {
     mockState.clear();
   });
 
-  it('renders input prompt', () => {
+  it('renders input prompt with system message', async () => {
     const { lastFrame } = render(
       <Chat model="gemma4" onCommand={vi.fn()} autoExecute={false} />,
     );
-    expect(lastFrame()).toContain('>');
+    await tick();
+    const frame = lastFrame() ?? '';
+    // System message should be present (dimmed, but visible)
+    expect(frame).toContain('coding assistant');
+    expect(frame).toContain('>');
   });
 
   it('shows message after submit', async () => {
     const chat = (
       <Chat model="gemma4" onCommand={vi.fn()} autoExecute={false} />
     );
     const { lastFrame, rerender } = render(chat);
+    await tick();
     await typeText(rerender, 'hello', chat);
     submitInput('hello');
     rerender(chat);
     await waitForStream();
-    expect(lastFrame()).toContain('hello');
+    const frame = lastFrame() ?? '';
+    expect(frame).toContain('coding assistant');
+    expect(frame).toContain('hello');
   });
 
   it('clears input after submit', async () => {
     const chat = (
       <Chat model="gemma4" onCommand={vi.fn()} autoExecute={false} />
     );
     const { lastFrame, rerender } = render(chat);
+    await tick();
     await typeText(rerender, 'hello', chat);
     submitInput('hello');
     rerender(chat);
     await waitForStream();
     // Verify the user message appears in the chat
-    expect(lastFrame()).toContain('hello');
+    const frame = lastFrame() ?? '';
+    expect(frame).toContain('coding assistant');
+    expect(frame).toContain('hello');
   });
 
   it('does not add blank messages', async () => {
     const chat = (
       <Chat model="gemma4" onCommand={vi.fn()} autoExecute={false} />
     );
     const { lastFrame, rerender } = render(chat);
+    await tick();
+    const beforeFrame = lastFrame() ?? '';
+    const systemLineCount = beforeFrame.split('\n').length;
     await typeText(rerender, '   ', chat);
     submitInput('   ');
     rerender(chat);
     await tick();
-    const frame = lastFrame() ?? '';
-    const lines = frame
-      .split('\n')
-      .filter(
-        (line) => line.trim() && !line.includes('>') && !line.includes('Mode:'),
-      );
-    expect(lines).toHaveLength(0);
+    const afterFrame = lastFrame() ?? '';
+    const afterLineCount = afterFrame.split('\n').length;
+    // After submitting blank input, line count should not increase
+    // (no new user message added)
+    expect(afterLineCount).toBe(systemLineCount);
+    expect(afterFrame).toContain('coding assistant');
   });
 
   it('shows multiple messages in order', async () => {
     const chat = (
       <Chat model="gemma4" onCommand={vi.fn()} autoExecute={false} />
     );
     const { lastFrame, rerender } = render(chat);
+    await tick();
     await typeText(rerender, 'first', chat);
     submitInput('first');
     rerender(chat);
@@ -166,9 +164,11 @@ describe('Chat', () => {
     rerender(chat);
     await waitForStream();
     const frame = lastFrame() ?? '';
+    const systemIdx = frame.indexOf('coding assistant');
     const firstIdx = frame.indexOf('first');
     const secondIdx = frame.indexOf('second');
-    expect(firstIdx).toBeGreaterThanOrEqual(0);
+    expect(systemIdx).toBeGreaterThanOrEqual(0);
+    expect(firstIdx).toBeGreaterThan(systemIdx);
     expect(secondIdx).toBeGreaterThan(firstIdx);
   });
 

src/components/Chat.tsx

@@ -2,7 +2,7 @@ import { Box } from 'ink';
 import { useCallback, useState } from 'react';
 
 import { ROLE, TOOL } from '../constants';
-import { ollama, tools } from '../utils';
+import { agents, ollama, tools } from '../utils';
 import { Autocomplete } from './Autocomplete';
 import { Messages } from './Messages';
 import { ToolApproval } from './ToolApproval';
@@ -14,7 +14,9 @@ interface Props {
 }
 
 export function Chat({ model, onCommand, autoExecute }: Props) {
-  const [messages, setMessages] = useState<ollama.Message[]>([]);
+  const [messages, setMessages] = useState<ollama.Message[]>([
+    agents.createSystemMessage(),
+  ]);
   const [submitKey, setSubmitKey] = useState(0);
   const [isLoading, setIsLoading] = useState(false);
   const [pendingToolCall, setPendingToolCall] =

src/constants/index.ts

@@ -1,6 +1,7 @@
 export * from './commands';
 export * as KEY from './key';
 export * as PACKAGE from './package';
+export * as PROMPT from './prompt';
 export * from './role';
 export * as TOOL from './tool';
 export * as UI from './ui';

src/constants/prompt.ts

@@ -0,0 +1,25 @@
+export const BASE_SYSTEM_PROMPT = `You are a coding assistant that helps users write, edit, and understand code. You have access to tools for reading files, writing files, running shell commands, and searching code
+
+Follow these rules:
+1. Always use available tools rather than guessing file contents or code behavior
+2. Read files before editing them to understand context
+3. When writing files, provide complete, working code
+4. Explain your reasoning when making non-trivial changes
+5. Prefer minimal changes that achieve the goal
+6. Confirm with the user before destructive operations
+
+When tools return results, incorporate them into your response naturally`;
+
+export const TOOL_INSTRUCTIONS = `Available tools:
+- read_file: Read file contents at a path
+- write_file: Write content to a file (requires approval)
+- edit_file: Make precise edits to a file
+- list_dir: List files in a directory
+- grep_search: Search code with regex
+- run_shell: Execute shell commands (requires approval)
+
+Always use tools when you need to:
+- Check file contents before referencing them
+- Make file changes
+- Explore project structure
+- Search the codebase`;

src/utils/agents.test.ts

@@ -0,0 +1,53 @@
+import { existsSync, readFileSync } from 'node:fs';
+
+import { ROLE } from '../constants';
+import { BASE_SYSTEM_PROMPT, TOOL_INSTRUCTIONS } from '../constants/prompt';
+
+vi.mock('node:fs');
+
+describe('agents', () => {
+  it('creates system message with base prompt', async () => {
+    const { createSystemMessage } = await import('./agents');
+    const message = createSystemMessage();
+
+    expect(message.role).toBe(ROLE.SYSTEM);
+    expect(message.content).toContain(BASE_SYSTEM_PROMPT);
+    expect(message.content).toContain(TOOL_INSTRUCTIONS);
+  });
+
+  it('includes AGENTS.md content when available', async () => {
+    vi.mocked(existsSync).mockReturnValue(true);
+    vi.mocked(readFileSync).mockReturnValue('## Test Project\nTest context');
+
+    const { buildSystemPrompt } = await import('./agents');
+    const prompt = buildSystemPrompt();
+
+    expect(prompt).toContain('Project context from AGENTS.md:');
+    expect(prompt).toContain('## Test Project');
+    expect(prompt).toContain('Test context');
+  });
+
+  it('works without AGENTS.md', async () => {
+    vi.mocked(existsSync).mockReturnValue(false);
+
+    const { buildSystemPrompt } = await import('./agents');
+    const prompt = buildSystemPrompt();
+
+    expect(prompt).not.toContain('Project context from AGENTS.md:');
+    expect(prompt).toContain(BASE_SYSTEM_PROMPT);
+  });
+
+  it('handles read file error gracefully', async () => {
+    vi.mocked(existsSync).mockReturnValue(true);
+    vi.mocked(readFileSync).mockImplementation(() => {
+      throw new Error('Permission denied');
+    });
+
+    const { buildSystemPrompt } = await import('./agents');
+    const prompt = buildSystemPrompt();
+
+    // Should not include AGENTS.md content when read fails
+    expect(prompt).not.toContain('Project context from AGENTS.md:');
+    expect(prompt).toContain(BASE_SYSTEM_PROMPT);
+  });
+});

src/utils/agents.ts

@@ -0,0 +1,43 @@
+import { existsSync, readFileSync } from 'node:fs';
+import { join } from 'node:path';
+
+import { ROLE } from '../constants';
+import { BASE_SYSTEM_PROMPT, TOOL_INSTRUCTIONS } from '../constants/prompt';
+import type * as ollama from './ollama';
+
+const AGENTS_FILE = 'AGENTS.md';
+
+function loadAgentsContent(): string | null {
+  const cwd = process.cwd();
+  const agentsPath = join(cwd, AGENTS_FILE);
+
+  if (!existsSync(agentsPath)) {
+    return null;
+  }
+
+  try {
+    return readFileSync(agentsPath, 'utf8');
+  } catch {
+    return null;
+  }
+}
+
+export function buildSystemPrompt(): string {
+  const parts: string[] = [BASE_SYSTEM_PROMPT];
+
+  const agentsContent = loadAgentsContent();
+  if (agentsContent) {
+    parts.push('\n\nProject context from AGENTS.md:\n', agentsContent);
+  }
+
+  parts.push('\n\n', TOOL_INSTRUCTIONS);
+
+  return parts.join('');
+}
+
+export function createSystemMessage(): ollama.Message {
+  return {
+    role: ROLE.SYSTEM,
+    content: buildSystemPrompt(),
+  };
+}

src/utils/index.ts

@@ -1,3 +1,4 @@
+export * as agents from './agents';
 export * as config from './config';
 export * as ollama from './ollama';
 export * as screen from './screen';