fix: guard _resize against disposed _resizeDebouncer (fixes #317787)

[vs-code-engineering]

🔧 Error Fix

Summary

Error: Cannot read properties of undefined (reading 'resize') in terminalInstance._resize

Root cause: Commit dff2ee20 ("fix: dispose resize debouncer before process manager to prevent race", part of #315284) moved _resizeDebouncer disposal earlier in the terminal teardown sequence — before _processManager.dispose(). This prevents resize callbacks from reaching a nulled ptyProcessReady, but introduces a new race: configuration change events (e.g. from terminalSuggestConfiguration registration) can fire during the dispose sequence and trigger setVisible → _resize, which crashes because _resizeDebouncer is already undefined.

Impact: 195 affected users across 4 coalesced buckets on all platforms.

Fixes #317787
Recommended reviewer: @Tyriar

Culprit Commit

Field	Value
Commit	dff2ee20
Title	fix: guard setDimensions against disposed ptyProcessReady (fixes #315282) (#315284)
Author	@vs-code-engineering[bot] / @bryanchen-d (co-author)
Date	2026-05-19
Regression window	553c727...e9f40e5 (May 18 16:12 → May 18 23:45)

Code Flow

sequenceDiagram
    participant User
    participant TI as TerminalInstance
    participant RD as ResizeDebouncer
    participant CS as ConfigService
    participant TSC as TerminalSuggestConfig

    User->>TI: dispose()
    TI->>RD: dispose()
    Note over TI: _resizeDebouncer = undefined
    TI->>CS: (dispose continues...)
    TSC->>CS: updateConfigurations()
    CS->>TI: onDidChangeConfiguration fires
    TI->>TI: setVisible(_isVisible)
    TI->>TI: _resize()
    Note over TI: this._resizeDebouncer!.resize() 💥 undefined

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Affected Files

File	Role
src/vs/workbench/contrib/terminal/browser/terminalInstance.ts	Crash site — _resize uses _resizeDebouncer! after it's been disposed
src/vs/workbench/contrib/terminalContrib/suggest/common/terminalSuggestConfiguration.ts	Triggers configuration registration during startup that fires config change events

Repro Steps

1. Open a terminal in VS Code
2. Close/dispose the terminal while a terminal suggest configuration is being registered
3. The config change event fires setVisible → _resize after _resizeDebouncer is already disposed
4. TypeError thrown at _resizeDebouncer!.resize()

How the Fix Works

Chosen approach (src/vs/workbench/contrib/terminal/browser/terminalInstance.ts):

Added !this._resizeDebouncer to the existing early-return guard at the top of _resize(). When _resizeDebouncer is undefined (meaning the instance is mid-disposal), the method returns immediately before any resize logic executes. This is a guard clause upstream of the crash site — it prevents the error from being produced rather than catching it after the fact. Also replaced the ! non-null assertion on the .resize() call with optional chaining (?.) as a safety net against any other path that could reach this line post-disposal.

This follows the principle of fixing at the data producer (the disposal sequence that nulls _resizeDebouncer) by guarding callers that can still fire during that window, rather than wrapping the crash in try/catch.

Recommended Owner

Owner	Reason
@Tyriar	Primary owner of terminal infrastructure; authored disposal ordering logic

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