feat(tui,coding-agent): add OSC 9;4 terminal progress indicators

Emit OSC 9;4 progress start/end sequences during agent streaming and
compaction so terminals (iTerm2, WezTerm, Windows Terminal, Kitty, etc.)
show activity in their tab bar.

Made with love for @lucasmeijer

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,18 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added OSC 9;4 terminal progress indicators during agent streaming and compaction, so terminals like iTerm2, WezTerm, Windows Terminal, and Kitty show activity in their tab bar
+
+### Breaking Changes
+
+- Session-replacement commands now invalidate captured pre-replacement session-bound extension objects after `ctx.newSession()`, `ctx.fork()`, and `ctx.switchSession()`. Old `pi` and command `ctx` references now throw instead of silently targeting the replaced session. Migration: move post-switch work into `withSession`, and use only the `ReplacedSessionContext` passed to that callback for session-bound operations such as `sendUserMessage()`, `sendMessage()`, and `sessionManager` access.
+
+### Fixed
+
+- Fixed extension session-replacement flows so `ctx.newSession()`, `ctx.fork()`, `ctx.switchSession()`, and imported-session replacements fully rebind before post-switch work runs, added `withSession` replacement callbacks with fresh `ReplacedSessionContext` helpers, and make stale pre-replacement `pi` / `ctx` session-bound accesses throw instead of silently targeting the wrong session ([#2860](https://github.com/badlogic/pi-mono/issues/2860))
+
 ## [0.68.1] - 2026-04-22
 
 ### New Features

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

@@ -50,6 +50,7 @@ import {
 import { type AgentSession, type AgentSessionEvent, parseSkillBlock } from "../../core/agent-session.js";
 import { type AgentSessionRuntime, SessionImportFileNotFoundError } from "../../core/agent-session-runtime.js";
 import type {
+	ExtensionCommandContext,
 	ExtensionContext,
 	ExtensionRunner,
 	ExtensionUIContext,
@@ -307,6 +308,9 @@ export class InteractiveMode {
 		private options: InteractiveModeOptions = {},
 	) {
 		this.runtimeHost = runtimeHost;
+		this.runtimeHost.setRebindSession(async () => {
+			await this.rebindCurrentSession();
+		});
 		this.version = VERSION;
 		this.ui = new TUI(new ProcessTerminal(), this.settingsManager.getShowHardwareCursor());
 		this.ui.setClearOnShrink(this.settingsManager.getClearOnShrink());
@@ -594,17 +598,11 @@ export class InteractiveMode {
 		this.isInitialized = true;
 
 		// Initialize extensions first so resources are shown before messages
-		await this.bindCurrentSessionExtensions();
+		await this.rebindCurrentSession();
 
 		// Render initial messages AFTER showing loaded resources
 		this.renderInitialMessages();
 
-		// Set terminal title
-		this.updateTerminalTitle();
-
-		// Subscribe to agent events
-		this.subscribeToAgent();
-
 		// Set up theme file watcher
 		onThemeChange(() => {
 			this.ui.invalidate();
@@ -1434,7 +1432,6 @@ export class InteractiveMode {
 					try {
 						const result = await this.runtimeHost.newSession(options);
 						if (!result.cancelled) {
-							await this.handleRuntimeSessionChange();
 							this.renderCurrentSessionState();
 							this.ui.requestRender();
 						}
@@ -1447,7 +1444,6 @@ export class InteractiveMode {
 					try {
 						const result = await this.runtimeHost.fork(entryId, options);
 						if (!result.cancelled) {
-							await this.handleRuntimeSessionChange();
 							this.renderCurrentSessionState();
 							this.editor.setText(result.selectedText ?? "");
 							this.showStatus("Forked to new session");
@@ -1477,9 +1473,8 @@ export class InteractiveMode {
 					void this.flushCompactionQueue({ willRetry: false });
 					return { cancelled: false };
 				},
-				switchSession: async (sessionPath) => {
-					await this.handleResumeSession(sessionPath);
-					return { cancelled: false };
+				switchSession: async (sessionPath, options) => {
+					return this.handleResumeSession(sessionPath, options);
 				},
 				reload: async () => {
 					await this.handleReloadCommand();
@@ -1522,7 +1517,7 @@ export class InteractiveMode {
 		}
 	}
 
-	private async handleRuntimeSessionChange(): Promise<void> {
+	private async rebindCurrentSession(): Promise<void> {
 		this.resetExtensionUI();
 		this.unsubscribe?.();
 		this.unsubscribe = undefined;
@@ -2556,6 +2551,7 @@ export class InteractiveMode {
 
 		switch (event.type) {
 			case "agent_start":
+				this.ui.terminal.setProgress(true);
 				// Restore main escape handler if retry handler is still active
 				// (retry success event fires later, but we need main handler now)
 				if (this.retryEscapeHandler) {
@@ -2737,6 +2733,7 @@ export class InteractiveMode {
 			}
 
 			case "agent_end":
+				this.ui.terminal.setProgress(false);
 				if (this.loadingAnimation) {
 					this.loadingAnimation.stop();
 					this.loadingAnimation = undefined;
@@ -2755,6 +2752,7 @@ export class InteractiveMode {
 				break;
 
 			case "compaction_start": {
+				this.ui.terminal.setProgress(true);
 				// Keep editor active; submissions are queued during compaction.
 				this.autoCompactionEscapeHandler = this.defaultEditor.onEscape;
 				this.defaultEditor.onEscape = () => {
@@ -2778,6 +2776,7 @@ export class InteractiveMode {
 			}
 
 			case "compaction_end": {
+				this.ui.terminal.setProgress(false);
 				if (this.autoCompactionEscapeHandler) {
 					this.defaultEditor.onEscape = this.autoCompactionEscapeHandler;
 					this.autoCompactionEscapeHandler = undefined;
@@ -4005,7 +4004,6 @@ export class InteractiveMode {
 							return;
 						}
 
-						await this.handleRuntimeSessionChange();
 						this.renderCurrentSessionState();
 						this.editor.setText(result.selectedText ?? "");
 						done();
@@ -4039,7 +4037,6 @@ export class InteractiveMode {
 				return;
 			}
 
-			await this.handleRuntimeSessionChange();
 			this.renderCurrentSessionState();
 			this.editor.setText("");
 			this.showStatus("Cloned to new session");
@@ -4212,37 +4209,44 @@ export class InteractiveMode {
 		});
 	}
 
-	private async handleResumeSession(sessionPath: string): Promise<void> {
+	private async handleResumeSession(
+		sessionPath: string,
+		options?: Parameters<ExtensionCommandContext["switchSession"]>[1],
+	): Promise<{ cancelled: boolean }> {
 		if (this.loadingAnimation) {
 			this.loadingAnimation.stop();
 			this.loadingAnimation = undefined;
 		}
 		this.statusContainer.clear();
 		try {
-			const result = await this.runtimeHost.switchSession(sessionPath);
+			const result = await this.runtimeHost.switchSession(sessionPath, {
+				withSession: options?.withSession,
+			});
 			if (result.cancelled) {
-				return;
+				return result;
 			}
-			await this.handleRuntimeSessionChange();
 			this.renderCurrentSessionState();
 			this.showStatus("Resumed session");
+			return result;
 		} catch (error: unknown) {
 			if (error instanceof MissingSessionCwdError) {
 				const selectedCwd = await this.promptForMissingSessionCwd(error);
 				if (!selectedCwd) {
 					this.showStatus("Resume cancelled");
-					return;
+					return { cancelled: true };
 				}
-				const result = await this.runtimeHost.switchSession(sessionPath, selectedCwd);
+				const result = await this.runtimeHost.switchSession(sessionPath, {
+					cwdOverride: selectedCwd,
+					withSession: options?.withSession,
+				});
 				if (result.cancelled) {
-					return;
+					return result;
 				}
-				await this.handleRuntimeSessionChange();
 				this.renderCurrentSessionState();
 				this.showStatus("Resumed session in current cwd");
-				return;
+				return result;
 			}
-			await this.handleFatalRuntimeError("Failed to resume session", error);
+			return this.handleFatalRuntimeError("Failed to resume session", error);
 		}
 	}
 
@@ -4578,7 +4582,6 @@ export class InteractiveMode {
 				this.showStatus("Import cancelled");
 				return;
 			}
-			await this.handleRuntimeSessionChange();
 			this.renderCurrentSessionState();
 			this.showStatus(`Session imported from: ${inputPath}`);
 		} catch (error: unknown) {
@@ -4593,7 +4596,6 @@ export class InteractiveMode {
 					this.showStatus("Import cancelled");
 					return;
 				}
-				await this.handleRuntimeSessionChange();
 				this.renderCurrentSessionState();
 				this.showStatus(`Session imported from: ${inputPath}`);
 				return;
@@ -4949,7 +4951,6 @@ export class InteractiveMode {
 			if (result.cancelled) {
 				return;
 			}
-			await this.handleRuntimeSessionChange();
 			this.renderCurrentSessionState();
 			this.chatContainer.addChild(new Spacer(1));
 			this.chatContainer.addChild(new Text(`${theme.fg("accent", "✓ New session started")}`, 1, 1));
@@ -5127,6 +5128,7 @@ export class InteractiveMode {
 
 	stop(): void {
 		this.unregisterSignalHandlers();
+		this.ui.terminal.setProgress(false);
 		if (this.loadingAnimation) {
 			this.loadingAnimation.stop();
 			this.loadingAnimation = undefined;

packages/coding-agent/test/edit-tool-no-full-redraw.test.ts

@@ -27,6 +27,7 @@ class FakeTerminal implements Terminal {
 	clearFromCursor(): void {}
 	clearScreen(): void {}
 	setTitle(_title: string): void {}
+	setProgress(_active: boolean): void {}
 
 	get fullClearCount(): number {
 		return this.writes.filter((write) => write.includes("\x1b[2J\x1b[H\x1b[3J")).length;

packages/tui/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added `setProgress(active: boolean)` to the `Terminal` interface for OSC 9;4 progress indicator support
+
 ## [0.68.1] - 2026-04-22
 
 ### Fixed

packages/tui/src/terminal.ts

@@ -48,6 +48,9 @@ export interface Terminal {
 
 	// Title operations
 	setTitle(title: string): void; // Set terminal window title
+
+	// Progress indicator (OSC 9;4)
+	setProgress(active: boolean): void;
 }
 
 /**
@@ -357,4 +360,14 @@ export class ProcessTerminal implements Terminal {
 		// OSC 0;title BEL - set terminal window title
 		process.stdout.write(`\x1b]0;${title}\x07`);
 	}
+
+	setProgress(active: boolean): void {
+		if (active) {
+			// OSC 9;4;1;0 - indeterminate progress
+			process.stdout.write("\x1b]9;4;1;0\x07");
+		} else {
+			// OSC 9;4;0 - clear progress
+			process.stdout.write("\x1b]9;4;0;\x07");
+		}
+	}
 }

packages/tui/test/virtual-terminal.ts

@@ -100,6 +100,8 @@ export class VirtualTerminal implements Terminal {
 		this.xterm.write(`\x1b]0;${title}\x07`);
 	}
 
+	setProgress(_active: boolean): void {}
+
 	// Test-specific methods not in Terminal interface
 
 	/**