Fix terminal tool progress listener leak

[Dmitriy Vasyura (dmitrivMS)]

Summary

• stop each rendered terminal tool progress row from subscribing to the shared onDidContinueInBackground emitter
• route matching UI updates through TerminalChatService's existing active progress-part registry
• preserve the Agent Host event and update every active rendering of the matching terminal tool session
• add regression coverage with 50 actual rendered progress parts, including duplicate rows for one terminal session

Log evidence

The newest populated Insiders session (20260823T004915) reported:

[error] potential listener LEAK detected, popular: Error
    at ... onDidContinueInBackground
    at ... createToolInvocationSubPart

The allocation stack pointed to ChatTerminalToolProgressPart: every terminal tool row registered a listener on one service-wide emitter. A sufficiently long chat therefore crossed the listener threshold even though each row only cared about its own terminal tool session.

Fix

TerminalChatService.continueInBackground now walks its already-maintained active progress-part set and directly marks parts whose terminal tool session ID matches. This removes the O(number of rendered terminal rows) listeners while preserving duplicate-row updates and the service event consumed by Agent Host.

Validation

• npm run transpile-client
• focused rendered-part regression test: 1 passed
• combined ChatTerminalToolProgressPart and TerminalChatService suites: 23 passed
• the rendered-part test mounts 50 real rows, verifies the emitter listener count remains constant, and confirms both rows sharing one session ID update their toolbar state
• editor diagnostics: no errors in the changed files
• git diff --check

A fresh-session log reproduction was not practical because the original warning requires dozens of live terminal-tool rows. The regression test directly exercises 50 rendered rows.

Related issues

Related to #311225.
Related to #294050.

These are non-closing references: both reports cover broader memory-growth scenarios with additional retention paths, so this change may mitigate one contributor without establishing a complete fix.

[Copilot]

Pull request overview

Fixes terminal tool progress listener accumulation by routing updates through TerminalChatService.

Changes:

• Removes per-row background-event listeners.
• Updates all matching active progress parts centrally.
• Adds service-level regression coverage.

Show a summary per file

File	Description
terminalChatService.test.ts	Tests progress-part notification behavior.
terminalChatService.ts	Dispatches updates through the active-part registry.
terminal.ts	Extends the progress-part contract.
chatTerminalToolProgressPart.ts	Exposes session identity and direct update handling.

Review details

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• Files reviewed: 4/4 changed files
• Comments generated: 1
• Review effort level: Balanced

[Anthony Kim (anthonykim1)]

LGTM, thank you

• Seems like better design - although Im not sure how true of a leak it was given onDidContinueInBackground being wrapped in this._register) in this._register(this._terminalChatService.onDidContinueInBackground(.

cc Megan Rogge (@meganrogge)