feat(hooks): add text_delta event for streaming text monitoring

- New text_delta hook event fires for each chunk of streaming text
- Enables real-time monitoring of agent output
- Plan-mode hook now updates todo progress as [DONE:id] tags stream in
- Each todo item has unique ID for reliable tracking

packages/coding-agent/CHANGELOG.md

@@ -42,6 +42,7 @@
 - Hook API: `pi.registerShortcut(shortcut, options)` for hooks to register custom keyboard shortcuts (e.g., `shift+p`, `ctrl+shift+x`)
 - Hook API: `ctx.ui.setWidget(key, lines)` for multi-line status displays above the editor (todo lists, progress tracking)
 - Hook API: `theme.strikethrough(text)` for strikethrough text styling
+- Hook API: `text_delta` event for monitoring streaming assistant text in real-time
 - `/hotkeys` command now shows hook-registered shortcuts in a separate "Hooks" section
 - New example hook: `plan-mode.ts` - Claude Code-style read-only exploration mode:
   - Toggle via `/plan` command, `Shift+P` shortcut, or `--plan` CLI flag
@@ -49,6 +50,8 @@
   - Bash commands restricted to non-destructive operations (blocks `rm`, `mv`, `git commit`, `npm install`, etc.)
   - Interactive prompt after each response: execute plan, stay in plan mode, or refine
   - Todo list widget showing progress with checkboxes and strikethrough for completed items
+  - Each todo has a unique ID; agent marks items done by outputting `[DONE:id]`
+  - Real-time progress updates via streaming text monitoring
   - `/todos` command to view current plan progress
   - Shows `⏸ plan` indicator in footer when in plan mode, `📋 2/5` when executing
   - State persists across sessions (including todo progress)

packages/coding-agent/docs/hooks.md

@@ -306,6 +306,21 @@ pi.on("turn_end", async (event, ctx) => {
 });
 ```
 
+#### text_delta
+
+Fired for each chunk of streaming text from the assistant. Useful for real-time monitoring of agent output.
+
+```typescript
+pi.on("text_delta", async (event, ctx) => {
+  // event.text - the new text chunk
+  
+  // Example: watch for specific patterns in streaming output
+  if (event.text.includes("[DONE:")) {
+    // Handle completion marker
+  }
+});
+```
+
 #### context
 
 Fired before each LLM call. Modify messages non-destructively (session unchanged).

packages/coding-agent/examples/hooks/plan-mode.ts

@@ -291,12 +291,25 @@ export default function planModeHook(pi: HookAPI) {
 		}
 	});
 
-	// Check for [DONE:id] tags after each tool result (agent may output them in tool-related text)
-	pi.on("tool_result", async (_event, ctx) => {
+	// Watch for [DONE:id] tags in streaming text
+	pi.on("text_delta", async (event, ctx) => {
 		if (!executionMode || todoItems.length === 0) return;
-		// The actual checking happens in agent_end when we have the full message
-		// But we update status here to keep UI responsive
-		updateStatus(ctx);
+
+		const doneIds = findDoneTags(event.text);
+		if (doneIds.length === 0) return;
+
+		let changed = false;
+		for (const id of doneIds) {
+			const item = todoItems.find((t) => t.id === id);
+			if (item && !item.completed) {
+				item.completed = true;
+				changed = true;
+			}
+		}
+
+		if (changed) {
+			updateStatus(ctx);
+		}
 	});
 
 	// Inject plan mode context

packages/coding-agent/src/core/agent-session.ts

@@ -224,6 +224,15 @@ export class AgentSession {
 
 	/** Internal handler for agent events - shared by subscribe and reconnect */
 	private _handleAgentEvent = async (event: AgentEvent): Promise<void> => {
+		// Emit text_delta events to hooks for streaming text monitoring
+		if (
+			event.type === "message_update" &&
+			event.assistantMessageEvent.type === "text_delta" &&
+			this._hookRunner
+		) {
+			await this._hookRunner.emit({ type: "text_delta", text: event.assistantMessageEvent.delta });
+		}
+
 		// When a user message starts, check if it's from either queue and remove it BEFORE emitting
 		// This ensures the UI sees the updated queue state
 		if (event.type === "message_start" && event.message.role === "user") {

packages/coding-agent/src/core/hooks/types.ts

@@ -392,6 +392,16 @@ export interface AgentEndEvent {
 	messages: AgentMessage[];
 }
 
+/**
+ * Event data for text_delta event.
+ * Fired when new text is streamed from the assistant.
+ */
+export interface TextDeltaEvent {
+	type: "text_delta";
+	/** The new text chunk */
+	text: string;
+}
+
 /**
  * Event data for turn_start event.
  */
@@ -535,6 +545,7 @@ export type HookEvent =
 	| BeforeAgentStartEvent
 	| AgentStartEvent
 	| AgentEndEvent
+	| TextDeltaEvent
 	| TurnStartEvent
 	| TurnEndEvent
 	| ToolCallEvent
@@ -701,6 +712,7 @@ export interface HookAPI {
 	on(event: "turn_end", handler: HookHandler<TurnEndEvent>): void;
 	on(event: "tool_call", handler: HookHandler<ToolCallEvent, ToolCallEventResult>): void;
 	on(event: "tool_result", handler: HookHandler<ToolResultEvent, ToolResultEventResult>): void;
+	on(event: "text_delta", handler: HookHandler<TextDeltaEvent>): void;
 
 	/**
 	 * Send a custom message to the session. Creates a CustomMessageEntry that