Fix terminal listener leaks in task system

[Copilot]

The task system leaked memory by registering terminal event listeners to TerminalTaskSystem's global disposal store via this._register(). When terminals disposed, listeners remained in the global store, maintaining references to disposed terminals indefinitely.

Changes

Added per-terminal disposal tracking via DisposableStore to ITerminalData:

interface ITerminalData {
	terminal: ITerminalInstance;
	lastTask: string;
	group?: string;
	shellIntegrationNonce?: string;
+	disposables: DisposableStore;  // Tracks terminal-specific listeners
}

Listener registration changes:

• _doCreateTerminal: Removed global registration of onDisposed listeners (lines 1418, 1430, 1440)
• _createTerminal: Creates DisposableStore per terminal, registers onDisposed listener to it
• _reconnectToTerminals: Creates DisposableStore for reconnected terminals, registers listeners
• terminate: Uses terminal-specific store when available, falls back to global store
• Problem matcher: Uses terminal-specific store when available, falls back to global store

Disposal:

• _deleteTaskAndTerminal: Calls terminalData.disposables.dispose() to clean up all terminal-specific listeners

This ensures listeners are disposed when their terminal is disposed, preventing indefinite retention.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Tasks leaks terminals</issue_title>
<issue_description>Tasks ends up holding on to terminal instances indefinitely, leaking a bunch of memory.

Examples:

This listener is disposed if the terminal is disposed, but a reference to it is kept indefinitely as it's not deleted via this._store.delete:

vscode/src/vs/workbench/contrib/tasks/browser/terminalTaskSystem.ts

Lines 1566 to 1569 in 50e37a4

	const onDisposedListener = this._register(terminal.onDisposed(() => {
	this._deleteTaskAndTerminal(terminal, terminalData);
	onDisposedListener.dispose();
	}));

This type of thing happens in several places where the terminal is registered against TerminalTaskSystem but never released:

vscode/src/vs/workbench/contrib/tasks/browser/terminalTaskSystem.ts

Line 1410 in 50e37a4

this._register(reconnectedTerminal.onDisposed(onDisposed));

Needs a proper audit by capturing heap snapshots to chase down all the leaks.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Tasks leaks terminals #269006

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[Copilot]

Pull request overview

This PR addresses memory leaks in the task system by adding per-terminal disposal tracking. Previously, terminal event listeners were registered globally via TerminalTaskSystem's disposal store, causing disposed terminal references to be retained indefinitely.

Key changes:

• Added disposables: DisposableStore property to ITerminalData interface to track terminal-specific listeners
• Created per-terminal disposal stores in _createTerminal and _reconnectToTerminals
• Updated listener registration to use terminal-specific stores with fallback to global store
• Modified _deleteTaskAndTerminal to dispose terminal-specific listeners

[Copilot]

Memory leak: If a reconnected terminal is returned by _doCreateTerminal (line 1426-1432) and that terminal was already added to _terminals by _reconnectToTerminals (line 1472), this code will create a new DisposableStore and overwrite the existing entry. The old DisposableStore from the reconnection will never be disposed, leaking its listeners. Before creating a new entry, check if the terminal already exists in _terminals and reuse its DisposableStore, or dispose the old one before replacing it.

See below for a potential fix:

		const existingTerminalData = this._terminals[terminalKey];
		let terminalDisposables: DisposableStore;
		let terminalData: ITerminalData;
		if (existingTerminalData) {
			// Reuse the existing DisposableStore to avoid leaking listeners created during reconnection.
			terminalDisposables = existingTerminalData.disposables;
			existingTerminalData.terminal = terminal;
			existingTerminalData.lastTask = taskKey;
			existingTerminalData.group = group;
			existingTerminalData.shellIntegrationNonce = terminal.shellLaunchConfig.shellIntegrationNonce;
			terminalData = existingTerminalData;
		} else {
			terminalDisposables = new DisposableStore();
			terminalData = { terminal: terminal, lastTask: taskKey, group, shellIntegrationNonce: terminal.shellLaunchConfig.shellIntegrationNonce, disposables: terminalDisposables };
			terminalDisposables.add(terminal.onDisposed(() => {
				this._deleteTaskAndTerminal(terminal, terminalData);
			}));
			this._terminals[terminalKey] = terminalData;
		}

[Copilot]

Behavioral change: The removed onDisposed listeners from _doCreateTerminal used to fire TaskEvent.terminated when terminals were disposed. Now with the new implementation calling _deleteTaskAndTerminal, this event is no longer fired when terminals are disposed by users (outside of explicit task termination). Consider adding this._fireTaskEvent(TaskEvent.terminated(...)) to the onDisposed handler or within _deleteTaskAndTerminal to maintain the original behavior.

Suggested change

	this._deleteTaskAndTerminal(terminal, terminalData);
	this._deleteTaskAndTerminal(terminal, terminalData);
	this._fireTaskEvent(TaskEvent.terminated());

[Copilot]

Behavioral change: The removed onDisposed listeners from _doCreateTerminal used to fire TaskEvent.terminated when terminals were disposed. Now with the new implementation calling _deleteTaskAndTerminal, this event is no longer fired when terminals are disposed by users (outside of explicit task termination). Consider adding this._fireTaskEvent(TaskEvent.terminated(...)) to the onDisposed handler or within _deleteTaskAndTerminal to maintain the original behavior.

Suggested change

	terminalDisposables.add(terminal.onDisposed(() => {
	terminalDisposables.add(terminal.onDisposed(() => {
	const event: ITaskEvent = {
	kind: TaskEventKind.Terminated,
	task
	};
	this._fireTaskEvent(event);