sessions: address CCR feedback on single-pane refinements

- remove dead singlePaneEditorTitleAuxiliaryBarOrder const + void stmt
- remove unused ICommandService dependency from the base layout controller
  (and its now-dead test-harness stub)
- update SINGLE_PANE_SCENARIOS.md + desktopSessionLayoutController.md for the
  merged controller, transition-triggered R1, and the Toggle Details command

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/vs/sessions/SINGLE_PANE_SCENARIOS.md

@@ -112,13 +112,13 @@ The **auto-managed** tabs (the pinned Changes tab and the default File tab) are
 
 ## 5. Detail panel content (driven by the active tab)
 
-`DetailPanelController` maps the active editor tab to the detail content, **reveal-on-activate**:
+The single-pane layout controller (`SinglePaneDesktopSessionLayoutController`) maps the active editor tab to the detail content. By default the detail panel is **closed** for a created session (Editor-only); it is opened via **Toggle Details** (or restored per-session), and while visible its container follows the active tab (the one exception is restoring the detail after a transient browser-tab hide):
 
 | Active tab | Detail panel |
 |-----------|--------------|
-| **Changes** | Branch Changes file list + Checks — revealed when the Changes tab activates |
-| **File** (Explorer) | Files/Explorer tree — revealed when a File tab activates |
-| **Browser** | **Hidden** (transiently) while the Browser tab is active |
+| **Changes** | Branch Changes file list + Checks — shown (Changes container) while the detail is visible |
+| **File** (Explorer) | Files/Explorer tree — shown (Files container) while the detail is visible |
+| **Browser** | **Hidden** (transiently) while the Browser tab is active; restored when switching back |
 
 Rules:
 - **Reveal on activate, respect after.** Switching to a Changes/File tab reveals the detail with the
@@ -229,9 +229,9 @@ No side pane at all — the detail panel and managed tabs are not shown; the cha
 | Docked layout, hide/show editor, detail width, sash-reveal sync, grid | `browser/workbench.ts` |
 | Docked panel overlay + resize sash | `browser/dockedAuxiliaryBarController.ts` |
 | Editor tab bar kept visible when content hidden; sash-reveal trigger | `browser/parts/editorPart.ts` |
-| Active tab → detail container mapping (reveal-on-activate, browser transient) | `contrib/changes/browser/detailPanelController.ts` |
-| Managed Changes + File tabs (suppressed opens) | `contrib/changes/browser/changesTabController.ts` |
+| Active tab → detail container mapping (browser transient) | `contrib/layout/browser/singlePaneDesktopSessionLayoutController.ts` |
+| Managed Changes + File tabs (suppressed opens) | `contrib/layout/browser/singlePaneDesktopSessionLayoutController.ts` |
 | Startup controller selection | `contrib/layout/browser/sessions.layout.contribution.ts` |
-| New-session level-triggered editor hide (R1/R2) | `contrib/layout/browser/singlePaneDesktopSessionLayoutController.ts` |
+| New-session transition-triggered editor hide (R1) | `contrib/layout/browser/singlePaneDesktopSessionLayoutController.ts` |
 | Hide Editor chevron, Maximize, add-tab actions | `contrib/editor/browser/editor.contribution.ts`, `contrib/editor/browser/addTabActions.ts` |
-| Detail (aux bar) toggle | `browser/layoutActions.ts` |
+| Toggle Details command + editor-title item | `contrib/layout/browser/singlePaneDesktopSessionLayoutController.ts` |

src/vs/sessions/contrib/editor/browser/editor.contribution.ts

@@ -50,9 +50,7 @@ const editorTitleActionsWhen = ContextKeyExpr.and(
 	IsAuxiliaryWindowContext.toNegated(),
 	IsTopRightEditorGroupContext);
 const singlePaneEditorTitleMaximizeOrder = 1000000;
-const singlePaneEditorTitleAuxiliaryBarOrder = 1000001;
 const singlePaneEditorTitleHideEditorOrder = 999999;
-void singlePaneEditorTitleAuxiliaryBarOrder;
 
 class SinglePaneAddTabContribution extends Disposable implements IWorkbenchContribution {
 

src/vs/sessions/contrib/layout/browser/baseSessionLayoutController.ts

@@ -18,7 +18,6 @@ import { Categories } from '../../../../platform/action/common/actionCommonCateg
 import { Action2, registerAction2 } from '../../../../platform/actions/common/actions.js';
 import { IConfigurationService } from '../../../../platform/configuration/common/configuration.js';
 import { ContextKeyExpr, IContextKeyService } from '../../../../platform/contextkey/common/contextkey.js';
-import { ICommandService } from '../../../../platform/commands/common/commands.js';
 import { IInstantiationService, ServicesAccessor } from '../../../../platform/instantiation/common/instantiation.js';
 import { ILifecycleService } from '../../../../workbench/services/lifecycle/common/lifecycle.js';
 import { KeybindingWeight } from '../../../../platform/keybinding/common/keybindingsRegistry.js';
@@ -143,7 +142,6 @@ export abstract class BaseLayoutController extends Disposable {
 		@ISessionChangesService protected readonly _sessionChangesService: ISessionChangesService,
 		@IChangesViewService protected readonly _changesViewService: IChangesViewService,
 		@IViewDescriptorService protected readonly _viewDescriptorService: IViewDescriptorService,
-		@ICommandService protected readonly _commandService: ICommandService,
 		@IContextKeyService protected readonly _contextKeyService: IContextKeyService,
 		@IInstantiationService protected readonly _instantiationService: IInstantiationService,
 		@ILifecycleService protected readonly _lifecycleService: ILifecycleService,

src/vs/sessions/contrib/layout/browser/desktopSessionLayoutController.md

@@ -124,15 +124,18 @@ menu item, keybinding, and command-palette entry are inert.
 #### D11 — Single-pane new-session views are Files-only
 In single-pane detail-panel mode only, while a new (uncreated) workspace session view is active, the
 editor content is hidden by default so the editor tab bar and Files detail panel remain without showing
-editor content. The hide is driven by the **session and active editor**, not by the editor's visibility:
-`_registerSinglePaneNewSessionRules` hides the editor part whenever this is a new-session view whose active
-editor is not real content (the managed empty tab or none), and leaves it alone once a real file/browser
-editor is active. It deliberately does **not** react to the editor becoming visible, so an explicit reveal
-sticks — opening a file reveals the editor before the file becomes the active editor (Task 4), and toggling
-the detail panel off reveals the empty editor so the side pane does not vanish (Task 2). Spurious width-based
-reveals are blocked at the source via `setSuppressDockedEditorRevealSync(true)` while the view has no real
-content. The shared D3b/D9b new-session side-pane visibility state is unchanged: once the user hides the
-side pane for a new session, it stays hidden for later new sessions.
+editor content. The hide is **transition-triggered**: `_registerNewSessionRules` (a no-op base hook
+overridden by `SinglePaneDesktopSessionLayoutController`) hides the editor part when it **just became
+visible**, or when the new-session view was **just entered** with the editor already visible (an
+inherited-visible editor from the previous session), and only while the active editor is not real content
+(the managed empty tab or none). It leaves the editor alone once a real file/browser editor is active.
+Switching to a managed tab (e.g. the Files placeholder) while the editor is **already** visible does not
+hide it — only a visibility transition or entering the view does. An explicit reveal sticks — opening a
+file reveals the editor before the file becomes the active editor (Task 4), and toggling the detail panel
+off reveals the empty editor so the side pane does not vanish (Task 2); entering the view always resets to
+editor-closed, so a stale cross-session explicit reveal cannot carry over. A momentary width-based reveal
+(e.g. a sash drag) is re-hidden by the same rule. The shared D3b/D9b new-session side-pane visibility state
+is unchanged: once the user hides the side pane for a new session, it stays hidden for later new sessions.
 
 ### Scenario: a cramped (small) window
 On a small window there isn't room for the sessions sidebar, the editor, and the side pane all at once.
@@ -256,13 +259,14 @@ and hands control back once the user reopens the sessions sidebar manually.
   collapsing an already editor-only state) just captures the resulting state, so an explicit aux-bar hide
   — including one whose editor-only state is restored when the pane re-opens — is never turned into a
   collapse.
-- **Single-pane new-session rule [D11]** — `LayoutController` exposes
-  `_registerSinglePaneNewSessionRules` as a no-op hook. `SinglePaneDesktopSessionLayoutController`
-  overrides it with an `autorun` over the active session, multi-session state, and editor maximized
-  state; on entering an uncreated workspace session that is not a quick chat, it hides `EDITOR_PART` under
-  `suppressEditorPartAutoVisibility()` and remembers that session resource. The autorun does not read
-  editor visibility as an observable, so later editor reveals do not retrigger the hide. D3b continues to
-  open the Files container unless the shared new-session side-pane state says it is hidden.
+- **Single-pane new-session rule [D11]** — `LayoutController` exposes `_registerNewSessionRules` as a
+  no-op hook. `SinglePaneDesktopSessionLayoutController` overrides it with an `autorun` over the active
+  session, multi-session state, editor maximized state, the active editor, and **the editor-part
+  visibility**; on an uncreated workspace session that is not a quick chat, it hides `EDITOR_PART` (under
+  `suppressEditorPartAutoVisibility()`) when the editor just became visible or the view was just entered
+  with the editor visible, tracking the previous editor-visible / in-new-session-view values across runs so
+  a mere active-editor change (e.g. switching to the Files placeholder) does not retrigger the hide. D3b
+  continues to open the Files container unless the shared new-session side-pane state says it is hidden.
 - **Responsive sidebar [D7]** — `_registerResponsiveSidebar` derives `spaceConstrained = enabled && small
   && editor visible && aux-bar visible && !multipleSessionsVisible` from the experimental setting
   `sessions.layout.autoCollapseSessionsSidebar` (`observableConfigValue`, default `product.quality !==

src/vs/sessions/contrib/layout/test/browser/layoutControllerTestUtils.ts

@@ -10,7 +10,6 @@ import { constObservable, ISettableObservable, observableValue } from '../../../
 import { URI } from '../../../../../base/common/uri.js';
 import { isEqual } from '../../../../../base/common/resources.js';
 import { mock } from '../../../../../base/test/common/mock.js';
-import { ICommandEvent, ICommandService } from '../../../../../platform/commands/common/commands.js';
 import { Codicon } from '../../../../../base/common/codicons.js';
 import { TestConfigurationService } from '../../../../../platform/configuration/test/common/testConfigurationService.js';
 import { IConfigurationService } from '../../../../../platform/configuration/common/configuration.js';
@@ -161,7 +160,6 @@ export interface ITestLayoutHarness {
 	onDidChangeEditorMaximized: Emitter<void>;
 	onDidActiveEditorChange: Emitter<void>;
 	onWillOpenEditor: Emitter<IEditorWillOpenEvent>;
-	onDidExecuteCommand: Emitter<ICommandEvent>;
 	onDidCloseEditor: Emitter<{ editor: EditorInput }>;
 	onDidEditorsChange: Emitter<void>;
 	onDidLayoutMainContainer: Emitter<IDimension>;
@@ -238,7 +236,6 @@ export function createTestHarness(store: DisposableStore, options: ICreateOption
 		onDidChangeEditorMaximized: store.add(new Emitter<void>()),
 		onDidActiveEditorChange: store.add(new Emitter<void>()),
 		onWillOpenEditor: store.add(new Emitter<IEditorWillOpenEvent>()),
-		onDidExecuteCommand: store.add(new Emitter<ICommandEvent>()),
 		onDidCloseEditor: store.add(new Emitter<{ editor: EditorInput }>()),
 		onDidEditorsChange: store.add(new Emitter<void>()),
 		onDidLayoutMainContainer: store.add(new Emitter<IDimension>()),
@@ -307,9 +304,6 @@ export function createTestHarness(store: DisposableStore, options: ICreateOption
 	instaService.stub(IChangesViewService, new class extends mock<IChangesViewService>() {
 		override setChangesetId(): void { }
 	});
-	instaService.stub(ICommandService, new class extends mock<ICommandService>() {
-		override readonly onDidExecuteCommand = harness.onDidExecuteCommand.event;
-	});
 	instaService.stub(ILifecycleService, new class extends mock<ILifecycleService>() {
 		// Resolves only when a test opts in via `activateAux`, so the single-pane
 		// managed-tab / detail-panel behaviour is not spun up otherwise.