Fix terminal-editor shift-drop on detached instances

[Dmitriy Vasyura (dmitrivMS)]

• dispose terminal drag-and-drop observers when their instances detach from an editor container
• prevent deferred drag-and-drop initialization from attaching to a stale container
• add regression coverage for initialized and pending observers during terminal editor tab reuse

Fixes #311164

Co-authored-by: Vlad Gerasimov vlad@vlad.studio

[Copilot]

Copilot review overview

🟢 Approval recommended

The lifecycle fix is narrowly scoped and both relevant race conditions have regression coverage.

Review tier: Balanced
Findings: None

What changed in this PR

Fixes terminal editor drag-and-drop observers persisting after tab reuse.

Changes:

• Dispose drag-and-drop observers when detaching terminals.
• Guard deferred initialization against stale containers.
• Add regression tests for initialized and pending observers.

File	Description
terminalInstance.ts	Corrects drag-and-drop observer lifecycle.
terminalInstance.test.ts	Covers detach and deferred-initialization scenarios.

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[github-actions]

Screenshot Changes

Base: a8f49160 Current: bcdb178f

Changed (2)

imageCarousel/imageCarousel/SingleSectionMiddleImage/Dark

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imageCarousel/imageCarousel/SingleSectionMiddleImage/Light

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2 insignificant change(s) omitted (≤20 px, Δ≤2). See CI logs for details.

[Suryaansh Prithvijit Singh (Ultron09)]

Thanks Dmitriy Vasyura (@dmitrivMS) for adding the expanded end-to-end regression tests and carrying the fix forward from #332908!

Could you please include:
Co-authored-by: Ultron09 <connect.singha@gmail.com>
in the commit/squash message so contributor attribution is preserved upon merge? Thank you!

[Dmitriy Vasyura (dmitrivMS)]

Thanks Dmitriy Vasyura (Dmitriy Vasyura (@dmitrivMS)) for adding the expanded end-to-end regression tests and carrying the fix forward from #332908!

Could you please include: Co-authored-by: Ultron09 <connect.singha@gmail.com> in the commit/squash message so contributor attribution is preserved upon merge? Thank you!

Hmm... I didn't use your PR at all. I can add Co-authored-by: Vlad Gerasimov vlad@vlad.studio

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

Anthony Kim (@anthonykim1)

Matched files:

• src/vs/workbench/contrib/terminal/browser/terminalInstance.ts
• src/vs/workbench/contrib/terminal/test/browser/terminalInstance.test.ts

[Suryaansh Prithvijit Singh (Ultron09)]

Hi Dmitriy Vasyura (@dmitrivMS) — no worries at all! Just to clarify, the production fix in src/vs/workbench/contrib/terminal/browser/terminalInstance.ts (this._dndObserver.clear() in detachFromElement and the this._container !== container guard in attachToElement) was from PR #332908 which you approved earlier today before opening this PR to add the real instance drop tests.

Crediting Vlad as well for the earlier iteration in #318756 is great! Either way, really glad to see #311164 resolved. Thanks for shepherding it to completion!