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/coding-agent/CHANGELOG.md

@@ -2,8 +2,14 @@
 
 ## [Unreleased]
 
+### Added
+
+- **Streaming bash output**: Bash tool now streams output in real-time during execution. The TUI displays live progress with the last 5 lines visible (expandable with ctrl+o). ([#44](https://github.com/badlogic/pi-mono/issues/44))
+
 ### Changed
 
+- **Tool output display**: When collapsed, tool output now shows the last N lines instead of the first N lines, making streaming output more useful.
+
 - Updated `@mariozechner/pi-ai` with X-Initiator header support for GitHub Copilot, ensuring agent calls are not deducted from quota. ([#200](https://github.com/badlogic/pi-mono/pull/200) by [@kim0](https://github.com/kim0))
 
 ### Fixed

packages/coding-agent/docs/rpc.md

@@ -553,6 +553,7 @@ Events are streamed to stdout as JSON lines during agent operation. Events do NO
 | `message_update` | Streaming update (text/thinking/toolcall deltas) |
 | `message_end` | Message completes |
 | `tool_execution_start` | Tool begins execution |
+| `tool_execution_update` | Tool execution progress (streaming output) |
 | `tool_execution_end` | Tool completes |
 | `auto_compaction_start` | Auto-compaction begins |
 | `auto_compaction_end` | Auto-compaction completes |
@@ -645,9 +646,9 @@ Example streaming a text response:
 {"type":"message_update","message":{...},"assistantMessageEvent":{"type":"text_end","contentIndex":0,"content":"Hello world","partial":{...}}}
 ```
 
-### tool_execution_start / tool_execution_end
+### tool_execution_start / tool_execution_update / tool_execution_end
 
-Emitted when a tool begins and completes execution.
+Emitted when a tool begins, streams progress, and completes execution.
 
 ```json
 {
@@ -658,6 +659,23 @@ Emitted when a tool begins and completes execution.
 }
 ```
 
+During execution, `tool_execution_update` events stream partial results (e.g., bash output as it arrives):
+
+```json
+{
+  "type": "tool_execution_update",
+  "toolCallId": "call_abc123",
+  "toolName": "bash",
+  "args": {"command": "ls -la"},
+  "partialResult": {
+    "content": [{"type": "text", "text": "partial output so far..."}],
+    "details": {"truncation": null, "fullOutputPath": null}
+  }
+}
+```
+
+When complete:
+
 ```json
 {
   "type": "tool_execution_end",
@@ -671,7 +689,7 @@ Emitted when a tool begins and completes execution.
 }
 ```
 
-Use `toolCallId` to correlate `tool_execution_start` with `tool_execution_end`.
+Use `toolCallId` to correlate events. The `partialResult` in `tool_execution_update` contains the accumulated output so far (not just the delta), allowing clients to simply replace their display on each update.
 
 ### auto_compaction_start / auto_compaction_end
 

packages/coding-agent/src/core/tools/bash.ts

@@ -35,6 +35,7 @@ export const bashTool: AgentTool<typeof bashSchema> = {
 		_toolCallId: string,
 		{ command, timeout }: { command: string; timeout?: number },
 		signal?: AbortSignal,
+		onUpdate?,
 	) => {
 		return new Promise((resolve, reject) => {
 			const { shell, args } = getShellConfig();
@@ -92,6 +93,20 @@ export const bashTool: AgentTool<typeof bashSchema> = {
 					const removed = chunks.shift()!;
 					chunksBytes -= removed.length;
 				}
+
+				// Stream partial output to callback (truncated rolling buffer)
+				if (onUpdate) {
+					const fullBuffer = Buffer.concat(chunks);
+					const fullText = fullBuffer.toString("utf-8");
+					const truncation = truncateTail(fullText);
+					onUpdate({
+						content: [{ type: "text", text: truncation.content || "" }],
+						details: {
+							truncation: truncation.truncated ? truncation : undefined,
+							fullOutputPath: tempFilePath,
+						},
+					});
+				}
 			};
 
 			// Collect stdout and stderr together

packages/coding-agent/src/modes/interactive/components/tool-execution.ts

@@ -44,6 +44,7 @@ export class ToolExecutionComponent extends Container {
 	private args: any;
 	private expanded = false;
 	private showImages: boolean;
+	private isPartial = false;
 	private result?: {
 		content: Array<{ type: string; text?: string; data?: string; mimeType?: string }>;
 		isError: boolean;
@@ -66,12 +67,16 @@ export class ToolExecutionComponent extends Container {
 		this.updateDisplay();
 	}
 
-	updateResult(result: {
-		content: Array<{ type: string; text?: string; data?: string; mimeType?: string }>;
-		details?: any;
-		isError: boolean;
-	}): void {
+	updateResult(
+		result: {
+			content: Array<{ type: string; text?: string; data?: string; mimeType?: string }>;
+			details?: any;
+			isError: boolean;
+		},
+		isPartial = false,
+	): void {
 		this.result = result;
+		this.isPartial = isPartial;
 		this.updateDisplay();
 	}
 
@@ -86,11 +91,11 @@ export class ToolExecutionComponent extends Container {
 	}
 
 	private updateDisplay(): void {
-		const bgFn = this.result
-			? this.result.isError
+		const bgFn = this.isPartial
+			? (text: string) => theme.bg("toolPendingBg", text)
+			: this.result?.isError
 				? (text: string) => theme.bg("toolErrorBg", text)
-				: (text: string) => theme.bg("toolSuccessBg", text)
-			: (text: string) => theme.bg("toolPendingBg", text);
+				: (text: string) => theme.bg("toolSuccessBg", text);
 
 		this.contentText.setCustomBgFn(bgFn);
 		this.contentText.setText(this.formatToolExecution());
@@ -164,13 +169,15 @@ export class ToolExecutionComponent extends Container {
 				if (output) {
 					const lines = output.split("\n");
 					const maxLines = this.expanded ? lines.length : 5;
-					const displayLines = lines.slice(0, maxLines);
-					const remaining = lines.length - maxLines;
+					const skipped = Math.max(0, lines.length - maxLines);
+					const displayLines = lines.slice(-maxLines);
 
-					text += "\n\n" + displayLines.map((line: string) => theme.fg("toolOutput", line)).join("\n");
-					if (remaining > 0) {
-						text += theme.fg("toolOutput", `\n... (${remaining} more lines)`);
+					if (skipped > 0) {
+						text += theme.fg("toolOutput", `\n\n... (${skipped} earlier lines)`);
 					}
+					text +=
+						(skipped > 0 ? "\n" : "\n\n") +
+						displayLines.map((line: string) => theme.fg("toolOutput", line)).join("\n");
 				}
 
 				// Show truncation warning at the bottom (outside collapsed area)

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -755,18 +755,19 @@ export class InteractiveMode {
 				break;
 			}
 
+			case "tool_execution_update": {
+				const component = this.pendingTools.get(event.toolCallId);
+				if (component) {
+					component.updateResult({ ...event.partialResult, isError: false }, true);
+					this.ui.requestRender();
+				}
+				break;
+			}
+
 			case "tool_execution_end": {
 				const component = this.pendingTools.get(event.toolCallId);
 				if (component) {
-					const resultData =
-						typeof event.result === "string"
-							? {
-									content: [{ type: "text" as const, text: event.result }],
-									details: undefined,
-									isError: event.isError,
-								}
-							: { content: event.result.content, details: event.result.details, isError: event.isError };
-					component.updateResult(resultData);
+					component.updateResult({ ...event.result, isError: event.isError });
 					this.pendingTools.delete(event.toolCallId);
 					this.ui.requestRender();
 				}
@@ -993,11 +994,7 @@ export class InteractiveMode {
 			} else if (message.role === "toolResult") {
 				const component = this.pendingTools.get(message.toolCallId);
 				if (component) {
-					component.updateResult({
-						content: message.content,
-						details: message.details,
-						isError: message.isError,
-					});
+					component.updateResult(message);
 					this.pendingTools.delete(message.toolCallId);
 				}
 			}