Avoid decoration shutdown listeners for detached terminals

[Dmitriy Vasyura (dmitrivMS)]

Summary

• remove the workbench lifecycle dependency from DecorationAddon
• let XtermTerminal, which already knows whether it is detached, own decoration shutdown cleanup
• register one decoration cleanup listener for regular terminals and none for detached terminals
• preserve normal addon disposal for detached terminals
• add end-to-end listener-count coverage through XtermTerminal

Root cause

Every DecorationAddon registered a listener on the singleton lifecycleService.onWillShutdown emitter. Agent chat output creates many detached terminals, so tool-heavy sessions eventually crossed the listener leak threshold.

Detached terminals already own and dispose their XtermTerminal; xterm disposal unloads the addon and DecorationAddon.dispose() clears its decorations. Their global shutdown subscription was therefore redundant.

Shutdown policy now belongs to XtermTerminal, which already owns options.detached. Regular terminals preserve the existing shutdown behavior by calling the addon's public clearDecorations() API from a host-owned listener. DecorationAddon no longer knows about workbench lifecycle or detached-terminal mode.

Validation

• npm run transpile-client
• focused detached-terminal listener regression: 1 passed
• full DecorationAddon and XtermTerminal suites: 25 passed
• the regular setup terminal adds exactly one shutdown listener
• 50 detached XtermTerminal instances add zero shutdown listeners
• editor diagnostics: no errors
• git diff --check

Related issues

Fixes #311557

Related to #311225
Related to #294050

The related crash reports contain this listener signature among several independent renderer and extension-host retention paths, so they are intentionally non-closing references.

[Copilot]

Pull request overview

Moves terminal decoration shutdown cleanup to XtermTerminal, preventing redundant lifecycle listeners for detached terminals.

Changes:

• Removes lifecycle coupling from DecorationAddon.
• Registers shutdown cleanup only for regular terminals.
• Adds regression coverage for listener counts.

Show a summary per file

File	Description
decorationAddon.ts	Removes lifecycle dependency and listener.
xtermTerminal.ts	Owns conditional shutdown cleanup.
xtermTerminal.test.ts	Verifies regular and detached listener counts.

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• Files reviewed: 3/3 changed files
• Comments generated: 0
• Review effort level: Balanced