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Expand README with AgentMessage/LLM conversion, event semantics, partial messages
- Explain AgentMessage vs LLM Message separation and why it's needed - Document conversion flow: AgentMessage -> transformContext -> convertToLlm -> LLM - Clarify that prompt/queueMessage/continue must convert to user or toolResult - Document message_start/end events for prompt() and queued messages - Explain message_update is assistant-only with partial content - Add pattern for handling partial messages in reactive UIs - Document agent.state.streamMessage for accessing current partial
This commit is contained in:
Mario Zechner
parent
b6d9442916
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f86dea2e4f
1 changed files with 146 additions and 14 deletions
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@ -26,11 +26,19 @@ const agent = new Agent({
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// Subscribe to events for reactive UI updates
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agent.subscribe((event) => {
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switch (event.type) {
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case 'message_start':
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console.log(`${event.message.role} message started`);
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break;
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case 'message_update':
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// Only emitted for assistant messages during streaming
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// event.message is partial - may have incomplete content
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for (const block of event.message.content) {
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if (block.type === 'text') process.stdout.write(block.text);
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}
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break;
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case 'message_end':
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console.log(`${event.message.role} message complete`);
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break;
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case 'tool_execution_start':
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console.log(`Calling ${event.toolName}...`);
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break;
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@ -44,17 +52,66 @@ await agent.prompt('Hello, world!');
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console.log(agent.state.messages);
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```
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## AgentMessage vs LLM Message
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The agent internally works with `AgentMessage`, a flexible type that can include:
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- Standard LLM messages (`user`, `assistant`, `toolResult`)
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- User messages with attachments
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- Custom app-specific message types (via declaration merging)
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LLMs only understand a subset: `user`, `assistant`, and `toolResult` messages with specific content formats. The `convertToLlm` function bridges this gap.
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### Why This Separation?
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1. **Rich UI state**: Store UI-specific data (attachments metadata, custom message types) alongside the conversation
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2. **Session persistence**: Save the full conversation state including app-specific messages
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3. **Context manipulation**: Transform messages before sending to LLM (compaction, injection, filtering)
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### The Conversion Flow
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```
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AgentMessage[] → transformContext() → AgentMessage[] → convertToLlm() → Message[] → LLM
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↑ (optional) (required)
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App state with custom types,
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attachments, UI metadata
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```
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### Constraints
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**Messages passed to `prompt()` or queued via `queueMessage()` must convert to LLM messages with `role: "user"` or `role: "toolResult"`.**
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When calling `continue()`, the last message in the context must also convert to `user` or `toolResult`. The LLM expects to respond to a user or tool result, not to its own assistant message.
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```typescript
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// OK: Standard user message
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await agent.prompt('Hello');
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// OK: Custom type that converts to user message
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await agent.prompt({ role: 'hookMessage', content: 'System notification', timestamp: Date.now() });
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// But convertToLlm must handle this:
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convertToLlm: (messages) => messages.map(m => {
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if (m.role === 'hookMessage') {
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return { role: 'user', content: m.content, timestamp: m.timestamp };
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}
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return m;
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})
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// ERROR: Cannot prompt with assistant message
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await agent.prompt({ role: 'assistant', content: [...], ... }); // Will fail at LLM
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```
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## Agent Options
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```typescript
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interface AgentOptions {
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initialState?: Partial<AgentState>;
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// Converts AgentMessage[] to LLM-compatible Message[] before each call.
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// Default: filters to user/assistant/toolResult and converts attachments.
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// Converts AgentMessage[] to LLM-compatible Message[] before each LLM call.
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// Default: filters to user/assistant/toolResult and converts image attachments.
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convertToLlm?: (messages: AgentMessage[]) => Message[] | Promise<Message[]>;
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// Transform context before convertToLlm (for pruning, injecting context, etc.)
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// Transform context before convertToLlm (for pruning, compaction, injecting context)
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transformContext?: (messages: AgentMessage[], signal?: AbortSignal) => Promise<AgentMessage[]>;
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// Queue mode: 'all' sends all queued messages, 'one-at-a-time' sends one per turn
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@ -76,9 +133,9 @@ interface AgentState {
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model: Model<any>;
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thinkingLevel: ThinkingLevel; // 'off' | 'minimal' | 'low' | 'medium' | 'high' | 'xhigh'
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tools: AgentTool<any>[];
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messages: AgentMessage[];
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messages: AgentMessage[]; // Full conversation including custom types
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isStreaming: boolean;
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streamMessage: AgentMessage | null;
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streamMessage: AgentMessage | null; // Current partial message during streaming
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pendingToolCalls: Set<string>;
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error?: string;
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}
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@ -86,7 +143,9 @@ interface AgentState {
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## Events
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Events provide fine-grained lifecycle information for building reactive UIs:
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Events provide fine-grained lifecycle information for building reactive UIs.
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### Event Types
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| Event | Description |
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|-------|-------------|
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@ -95,12 +154,84 @@ Events provide fine-grained lifecycle information for building reactive UIs:
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| `turn_start` | New turn begins (one LLM response + tool executions) |
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| `turn_end` | Turn completes with assistant message and tool results |
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| `message_start` | Message begins (user, assistant, or toolResult) |
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| `message_update` | Assistant message streaming update |
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| `message_update` | **Assistant messages only.** Partial message during streaming |
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| `message_end` | Message completes |
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| `tool_execution_start` | Tool begins execution |
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| `tool_execution_update` | Tool streams progress |
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| `tool_execution_end` | Tool completes with result |
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### Message Events for prompt() and queueMessage()
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When you call `prompt(message)`, the agent emits `message_start` and `message_end` events for that message before the assistant responds:
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```
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prompt(userMessage)
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→ message_start { message: userMessage }
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→ message_end { message: userMessage }
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→ message_start { message: assistantMessage } // LLM starts responding
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→ message_update { message: partialAssistant } // streaming...
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→ message_end { message: assistantMessage }
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```
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Queued messages (via `queueMessage()`) emit the same events when injected:
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```
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// During tool execution, a message is queued
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agent.queueMessage(interruptMessage)
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// After tool completes, before next LLM call:
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→ message_start { message: interruptMessage }
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→ message_end { message: interruptMessage }
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→ message_start { message: assistantMessage } // LLM responds to interrupt
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...
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```
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### Handling Partial Messages in Reactive UIs
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`message_update` events contain partial assistant messages during streaming. The `event.message` may have:
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- Incomplete text (truncated mid-word)
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- Partial tool call arguments
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- Missing content blocks that haven't started streaming yet
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**Pattern for reactive UIs:**
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```typescript
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agent.subscribe((event) => {
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switch (event.type) {
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case 'message_start':
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if (event.message.role === 'assistant') {
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// Create placeholder in UI
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ui.addMessage({ id: tempId, role: 'assistant', content: [] });
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}
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break;
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case 'message_update':
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// Replace placeholder content with partial content
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// This is only emitted for assistant messages
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ui.updateMessage(tempId, event.message.content);
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break;
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case 'message_end':
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if (event.message.role === 'assistant') {
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// Finalize with complete message
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ui.finalizeMessage(tempId, event.message);
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}
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break;
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}
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});
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```
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**Accessing the current partial message:**
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During streaming, `agent.state.streamMessage` contains the current partial message. This is useful for rendering outside the event handler:
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```typescript
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// In a render loop or reactive binding
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if (agent.state.isStreaming && agent.state.streamMessage) {
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renderPartialMessage(agent.state.streamMessage);
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}
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```
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## Custom Message Types
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Extend `AgentMessage` for app-specific messages via declaration merging:
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@ -123,10 +254,10 @@ Custom messages are stored in state but filtered out by the default `convertToLl
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const agent = new Agent({
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convertToLlm: (messages) => {
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return messages
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.filter(m => m.role === 'user' || m.role === 'assistant' || m.role === 'toolResult')
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.filter(m => m.role !== 'notification') // Filter out UI-only messages
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.map(m => {
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// Convert custom types or pass through
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if (m.role === 'artifact') {
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// Convert to user message so LLM sees the artifact
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return { role: 'user', content: `[Artifact: ${m.language}]\n${m.code}`, timestamp: m.timestamp };
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}
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return m;
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@ -150,7 +281,7 @@ agent.queueMessage({
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});
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```
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When queued messages are detected after a tool call, remaining tool calls are skipped with error results.
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When queued messages are detected after a tool call, remaining tool calls are skipped with error results ("Skipped due to queued user message"). The queued message is then injected before the next assistant response.
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## Images
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@ -206,6 +337,7 @@ for await (const event of agentLoop(userMessage, context, config, undefined, str
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}
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// Continue from existing context (e.g., after overflow recovery)
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// Last message in context must convert to 'user' or 'toolResult'
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for await (const event of agentLoopContinue(context, config, undefined, streamSimple)) {
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console.log(event.type);
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}
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@ -217,14 +349,14 @@ for await (const event of agentLoopContinue(context, config, undefined, streamSi
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| Method | Description |
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|--------|-------------|
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| `prompt(text, attachments?)` | Send a user prompt |
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| `prompt(message)` | Send an AgentMessage directly |
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| `continue()` | Continue from current context |
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| `prompt(text, images?)` | Send a user prompt with optional images |
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| `prompt(message)` | Send an AgentMessage directly (must convert to user/toolResult) |
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| `continue()` | Continue from current context (last message must convert to user/toolResult) |
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| `abort()` | Abort current operation |
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| `waitForIdle()` | Promise that resolves when agent is idle |
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| `reset()` | Clear all messages and state |
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| `subscribe(fn)` | Subscribe to events, returns unsubscribe function |
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| `queueMessage(msg)` | Queue message for next turn |
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| `queueMessage(msg)` | Queue message for next turn (must convert to user/toolResult) |
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| `clearMessageQueue()` | Clear queued messages |
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### State Mutators
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