Add tool result streaming

- Add AgentToolUpdateCallback type and optional onUpdate callback to AgentTool.execute()
- Add tool_execution_update event with toolCallId, toolName, args, partialResult
- Normalize tool_execution_end to always use AgentToolResult (no more string fallback)
- Bash tool streams truncated rolling buffer output during execution
- ToolExecutionComponent shows last N lines when collapsed (not first N)
- Interactive mode handles tool_execution_update events
- Update RPC docs and ai/agent READMEs

fixes #44

packages/ai/src/agent/agent-loop.ts

@@ -243,7 +243,7 @@ async function executeToolCalls<T>(
 			args: toolCall.arguments,
 		});
 
-		let resultOrError: AgentToolResult<T> | string;
+		let result: AgentToolResult<T>;
 		let isError = false;
 
 		try {
@@ -252,10 +252,21 @@ async function executeToolCalls<T>(
 			// Validate arguments using shared validation function
 			const validatedArgs = validateToolArguments(tool, toolCall);
 
-			// Execute with validated, typed arguments
-			resultOrError = await tool.execute(toolCall.id, validatedArgs, signal);
+			// Execute with validated, typed arguments, passing update callback
+			result = await tool.execute(toolCall.id, validatedArgs, signal, (partialResult) => {
+				stream.push({
+					type: "tool_execution_update",
+					toolCallId: toolCall.id,
+					toolName: toolCall.name,
+					args: toolCall.arguments,
+					partialResult,
+				});
+			});
 		} catch (e) {
-			resultOrError = e instanceof Error ? e.message : String(e);
+			result = {
+				content: [{ type: "text", text: e instanceof Error ? e.message : String(e) }],
+				details: {} as T,
+			};
 			isError = true;
 		}
 
@@ -263,20 +274,16 @@ async function executeToolCalls<T>(
 			type: "tool_execution_end",
 			toolCallId: toolCall.id,
 			toolName: toolCall.name,
-			result: resultOrError,
+			result,
 			isError,
 		});
 
-		// Convert result to content blocks
-		const content: ToolResultMessage<T>["content"] =
-			typeof resultOrError === "string" ? [{ type: "text", text: resultOrError }] : resultOrError.content;
-
 		const toolResultMessage: ToolResultMessage<T> = {
 			role: "toolResult",
 			toolCallId: toolCall.id,
 			toolName: toolCall.name,
-			content,
-			details: typeof resultOrError === "string" ? ({} as T) : resultOrError.details,
+			content: result.content,
+			details: result.details,
 			isError,
 			timestamp: Date.now(),
 		};

packages/ai/src/agent/index.ts

@@ -1,3 +1,11 @@
 export { agentLoop, agentLoopContinue } from "./agent-loop.js";
 export * from "./tools/index.js";
-export type { AgentContext, AgentEvent, AgentLoopConfig, AgentTool, AgentToolResult, QueuedMessage } from "./types.js";
+export type {
+	AgentContext,
+	AgentEvent,
+	AgentLoopConfig,
+	AgentTool,
+	AgentToolResult,
+	AgentToolUpdateCallback,
+	QueuedMessage,
+} from "./types.js";

packages/ai/src/agent/types.ts

@@ -18,6 +18,9 @@ export interface AgentToolResult<T> {
 	details: T;
 }
 
+// Callback for streaming tool execution updates
+export type AgentToolUpdateCallback<T = any> = (partialResult: AgentToolResult<T>) => void;
+
 // AgentTool extends Tool but adds the execute function
 export interface AgentTool<TParameters extends TSchema = TSchema, TDetails = any> extends Tool<TParameters> {
 	// A human-readable label for the tool to be displayed in UI
@@ -26,6 +29,7 @@ export interface AgentTool<TParameters extends TSchema = TSchema, TDetails = any
 		toolCallId: string,
 		params: Static<TParameters>,
 		signal?: AbortSignal,
+		onUpdate?: AgentToolUpdateCallback<TDetails>,
 	) => Promise<AgentToolResult<TDetails>>;
 }
 
@@ -50,12 +54,20 @@ export type AgentEvent =
 	| { type: "message_end"; message: Message }
 	// Emitted when a tool execution starts
 	| { type: "tool_execution_start"; toolCallId: string; toolName: string; args: any }
+	// Emitted when a tool execution produces output (streaming)
+	| {
+			type: "tool_execution_update";
+			toolCallId: string;
+			toolName: string;
+			args: any;
+			partialResult: AgentToolResult<any>;
+	  }
 	// Emitted when a tool execution completes
 	| {
 			type: "tool_execution_end";
 			toolCallId: string;
 			toolName: string;
-			result: AgentToolResult<any> | string;
+			result: AgentToolResult<any>;
 			isError: boolean;
 	  }
 	// Emitted when a full turn completes