Replace @debounce with disposable RunOnceScheduler in TerminalResizeDebouncer

[bryanchen-d]

What

Replace the @debounce(100) decorator on _debounceResizeX with a RunOnceScheduler owned by the disposable store.

Why

The @debounce decorator schedules a bare setTimeout and stashes the handle as an instance field ($debounce$_debounceResizeX). The timer is not registered with any DisposableStore, so super.dispose() does not cancel it. The callback can fire after the terminal/xterm has been torn down and crash inside xterm.js' RenderService.get dimensions() — telemetry buckets aaa283a2, 4826565b, 1e83a096.

PR #314795 worked around this with an if (this._store.isDisposed) return; guard inside _debounceResizeX. That closes the buckets but:

• Every new debounced callsite on this class needs the same guard — forget it once and a new bucket appears (commit d1a4f1b added a similar guard to _resize three weeks later for the same class of race).
• The stray timer still fires; we just early-return.
• It's inconsistent with the rest of the codebase, where timers live in a DisposableStore (RunOnceScheduler, ThrottledDelayer, disposableTimeout, …) and are cancelled deterministically at dispose.

As Daniel noted on #314795:

moving off @debounce is the better option, this is a hack that doesn't truly fix the lifecycle.

Changes

terminalResizeDebouncer.ts:

• Replace @debounce(100) _debounceResizeX(cols) with a RunOnceScheduler registered via this._register(...). The scheduler reads this._latestX lazily (already updated before each schedule).
• Replace this._debounceResizeX(cols) with this._debounceResizeXScheduler.schedule().
• Cancel the scheduler in the immediate-resize branch and in flush() so a queued X-debounce cannot fire after a fresh full resize.
• Drop the import { debounce } and the per-callsite isDisposed guard inside the debounced method.

After this change, disposing the TerminalResizeDebouncer cancels the pending timer through the normal disposable chain — no post-dispose callback can run, so no guard is needed.

How to test

1. Open a terminal, type or generate >200 lines of output (debounce threshold).
2. Trigger dispose-during-resize:
   • Close (Ctrl+Shift+W) a terminal while resizing the window.
   • Toggle terminal.integrated.fontFamily immediately after killing a terminal.
   • Run exit in a long-running shell while the panel is mid-resize.
3. Verify no Cannot read properties of undefined (reading 'dimensions') in DevTools console.
4. Telemetry: bucket 4826565b (the _debounceResizeX path) should stop firing.

Risk

• Behavior in the live (non-disposed) path is identical: RunOnceScheduler.schedule() cancels and re-schedules a 100ms timer just like the decorator did, and reads the latest cols from _latestX which the caller updates before calling.
• The scheduler is cancelled in flush() and on immediate resize, so we cannot land a stale X-resize after a full resize — this was implicit before because clearTimeout did the same on the decorator's stored handle.

Refs #314795, #303546.

[Copilot]

Pull request overview

This PR replaces the @debounce(100)-based horizontal resize debounce in TerminalResizeDebouncer with a RunOnceScheduler that’s owned by the class’ disposable store, ensuring any pending timer is deterministically cancelled on dispose and avoiding post-dispose resize callbacks into torn-down xterm state.

Changes:

• Replaces the @debounce(100) decorator with a _debounceResizeXScheduler: RunOnceScheduler registered via this._register(...).
• Updates call sites to schedule/cancel the scheduler (including cancelling in the immediate-resize path and in flush()).
• Removes the debounce import and the isDisposed guard inside the previously-decorated method.

Show a summary per file

File	Description
src/vs/workbench/contrib/terminal/browser/terminalResizeDebouncer.ts	Moves horizontal resize debouncing to a disposable RunOnceScheduler and cancels pending work during flush/immediate resize to avoid post-dispose callbacks.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 1