sessions: preserve single pane dismissal state

[Sandeep Somavarapu (sandy081)]

Follow-up to #330573.

What changed

• avoid globally hiding the side pane when an editor closes while multiple Existing sessions are visible
• preserve a user-dismissed Files tab across Existing-to-Existing navigation while continuing to replace Changes in place
• keep empty-group default restoration and superseded-reconcile generation safety
• remove the unused PendingAuxiliaryBarRestore enum
• add focused multi-session close and session-switch dismissal coverage

Validation

• affected layout suites: 144 passing
• npm run compile
• npm run typecheck-client
• npm run valid-layers-check
• npm run hygiene
• git diff --check

[vs-code-engineering]

📬 CODENOTIFY

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

Benjamin Christopher Simmonds (@benibenj)

Matched files:

• src/vs/sessions/contrib/layout/browser/baseSessionLayoutController.ts
• src/vs/sessions/contrib/layout/browser/singlePane/singlePaneDockedTabsCoordinator.ts
• src/vs/sessions/contrib/layout/browser/singlePane/singlePaneExistingSessionStrategy.ts
• src/vs/sessions/contrib/layout/browser/singlePane/singlePaneVisibilityProfileStore.ts
• src/vs/sessions/contrib/layout/browser/singlePaneLayoutController.ts
• src/vs/sessions/contrib/layout/test/browser/desktopSessionLayoutController.test.ts
• src/vs/sessions/contrib/layout/test/browser/layoutControllerTestUtils.ts
• src/vs/sessions/contrib/layout/test/browser/singlePaneStrategies.test.ts

[Copilot]

Pull request overview

Refines single-pane session lifecycle behavior to preserve side-pane and managed-tab state across session navigation.

Changes:

• Prevents side-pane dismissal when multiple sessions are visible.
• Preserves dismissed Files tabs while replacing Changes tabs.
• Adds focused lifecycle regression tests and removes an unused enum.

Show a summary per file

File	Description
singlePaneStrategies.test.ts	Tests multi-session editor closure behavior.
desktopSessionLayoutController.test.ts	Tests managed-tab restoration and dismissal.
singlePaneVisibilityProfileStore.ts	Removes an unused enum.
singlePaneExistingSessionStrategy.ts	Avoids global pane hiding with multiple sessions.
singlePaneDockedTabsCoordinator.ts	Changes Files-tab reconciliation across session switches.

Review details

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• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Balanced