vscode/.github/skills/sessions/SKILL.md

name, description

name	description
sessions	Agent Sessions window architecture — covers the sessions-first app, layering, folder structure, chat widget, menus, contributions, entry points, and development guidelines. Use when implementing features or fixing issues in the Agent Sessions window.

When working on the Agent Sessions window (src/vs/sessions/), always follow these guidelines:

1. Read the Specification Documents First

The src/vs/sessions/ directory contains authoritative specification documents. Always read the relevant spec before making changes.

Document	Path	Covers
Layer spec	src/vs/sessions/README.md	Layering rules, dependency constraints, folder conventions
Layout spec	src/vs/sessions/LAYOUT.md	Grid structure, part positions, sizing, CSS classes, API reference
AI Customizations	src/vs/sessions/AI_CUSTOMIZATIONS.md	AI customization editor and tree view design
Chat Widget	src/vs/sessions/browser/widget/AGENTS_CHAT_WIDGET.md	Chat widget wrapper architecture, deferred session creation, option delivery
AI Customization Mgmt	src/vs/sessions/contrib/aiCustomizationManagement/browser/SPEC.md	Management editor specification
AI Customization Tree	src/vs/sessions/contrib/aiCustomizationTreeView/browser/SPEC.md	Tree view specification

If you modify the implementation, you must update the corresponding spec to keep it in sync. Update the Revision History table at the bottom of LAYOUT.md with a dated entry.

2. Architecture Overview

2.1 Layering

vs/base          ← Foundation utilities
vs/platform      ← Platform services
vs/editor        ← Text editor core
vs/workbench     ← Standard VS Code workbench
vs/sessions      ← Agent Sessions window (this layer)

Key constraint: vs/sessions may import from vs/workbench and all layers below it. vs/workbench must never import from vs/sessions.

2.2 Dependency Rules

• ✅ Import from vs/base, vs/platform, vs/editor, vs/workbench
• ✅ Import within vs/sessions (internal)
• ❌ Never import vs/sessions from vs/workbench
• Run npm run valid-layers-check to verify layering

2.3 How It Differs from VS Code

Aspect	VS Code Workbench	Agent Sessions Window
Layout	Configurable part positions	Fixed layout, no settings customization
Chrome	Activity bar, status bar, banner	Simplified — none of these
Primary UX	Editor-centric	Chat-first (Chat Bar is a primary part)
Editors	In the grid layout	Modal overlay above the workbench
Titlebar	Menubar, editor actions, layout controls	Session picker, run script, toggle sidebar/panel
Navigation	Activity bar with viewlets	Sidebar (views) + sidebar footer (account)
Entry point	vs/workbench workbench class	vs/sessions/browser/workbench.ts Workbench class

3. Folder Structure

src/vs/sessions/
├── README.md                               # Layer specification (read first)
├── LAYOUT.md                               # Authoritative layout specification
├── AI_CUSTOMIZATIONS.md                    # AI customization design document
├── sessions.common.main.ts                 # Common (browser + desktop) entry point
├── sessions.desktop.main.ts                # Desktop entry point (imports all contributions)
├── common/                                 # Shared types and context keys
│   └── contextkeys.ts                      # ChatBar context keys
├── browser/                                # Core workbench implementation
│   ├── workbench.ts                        # Main Workbench class (implements IWorkbenchLayoutService)
│   ├── menus.ts                            # Agent sessions menu IDs (Menus export)
│   ├── layoutActions.ts                    # Layout toggle actions (sidebar, panel, auxiliary bar)
│   ├── paneCompositePartService.ts         # AgenticPaneCompositePartService
│   ├── style.css                           # Layout-specific styles
│   ├── widget/                             # Agent sessions chat widget
│   │   ├── AGENTS_CHAT_WIDGET.md           # Chat widget architecture doc
│   │   ├── agentSessionsChatWidget.ts      # Main wrapper around ChatWidget
│   │   ├── agentSessionsChatTargetConfig.ts # Observable target state
│   │   ├── agentSessionsTargetPickerActionItem.ts # Target picker for input toolbar
│   │   └── media/
│   └── parts/                              # Workbench part implementations
│       ├── parts.ts                        # AgenticParts enum
│       ├── titlebarPart.ts                 # Titlebar (3-section toolbar layout)
│       ├── sidebarPart.ts                  # Sidebar (with footer for account widget)
│       ├── chatBarPart.ts                  # Chat Bar (primary chat surface)
│       ├── auxiliaryBarPart.ts             # Auxiliary Bar (with run script dropdown)
│       ├── panelPart.ts                    # Panel (terminal, output, etc.)
│       ├── projectBarPart.ts              # Project bar (folder entries)
│       ├── agentSessionsChatInputPart.ts   # Chat input part adapter
│       ├── agentSessionsChatWelcomePart.ts # Welcome view (mascot + target buttons + pickers)
│       └── media/                          # Part CSS files
├── electron-browser/                       # Desktop-specific entry points
│   ├── sessions.main.ts                    # Desktop main bootstrap
│   ├── sessions.ts                         # Electron process entry
│   ├── sessions.html                       # Production HTML shell
│   └── sessions-dev.html                   # Development HTML shell
└── contrib/                                # Feature contributions
    ├── accountMenu/browser/                # Account widget for sidebar footer
    ├── aiCustomizationManagement/browser/  # AI customization management editor
    ├── aiCustomizationTreeView/browser/    # AI customization tree view sidebar
    ├── changesView/browser/                # File changes view
    ├── chat/browser/                       # Chat actions (run script, branch, prompts)
    ├── configuration/browser/              # Configuration overrides
    └── sessions/browser/                   # Sessions view, title bar widget, active session service

4. Layout

Use the agent-sessions-layout skill for detailed guidance on the layout. Key points:

4.1 Visual Layout

┌─────────┬───────────────────────────────────────────────────────┐
│         │                    Titlebar                           │
│         ├────────────────────────────────────┬──────────────────┤
│ Sidebar │              Chat Bar              │  Auxiliary Bar   │
│         ├────────────────────────────────────┴──────────────────┤
│         │                      Panel                            │
└─────────┴───────────────────────────────────────────────────────┘

• Sidebar spans full window height (root grid level)
• Titlebar is inside the right section
• Chat Bar is the primary interaction surface
• Panel is hidden by default (terminal, output, etc.)
• Editor appears as a modal overlay, not in the grid

4.2 Parts

Part	Default Visibility	Notes
Titlebar	Always visible	3-section toolbar (left/center/right)
Sidebar	Visible	Sessions view, AI customization tree
Chat Bar	Visible	Primary chat widget
Auxiliary Bar	Visible	Changes view, etc.
Panel	Hidden	Terminal, output
Editor	Hidden	Main part hidden; editors open via MODAL_GROUP into ModalEditorPart

Not included: Activity Bar, Status Bar, Banner.

4.3 Editor Modal

The main editor part is hidden (display:none). All editors open via MODAL_GROUP into the standard ModalEditorPart overlay (created on-demand by EditorParts.createModalEditorPart). The sessions configuration sets workbench.editor.useModal to 'all', which causes findGroup() to redirect all editor opens to the modal. Click backdrop or press Escape to dismiss.

5. Chat Widget

The Agent Sessions chat experience is built around AgentSessionsChatWidget — a wrapper around the core ChatWidget that adds:

• Deferred session creation — the UI is interactive before any session resource exists; sessions are created on first message send
• Target configuration — observable state tracking which agent provider (Local, Cloud) is selected
• Welcome view — branded empty state with mascot, target buttons, option pickers, and input slot
• Initial session options — option selections travel atomically with the first request
• Configurable picker placement — pickers can appear in welcome view, input toolbar, or both

Read browser/widget/AGENTS_CHAT_WIDGET.md for the full architecture.

Key classes:

• AgentSessionsChatWidget (browser/widget/agentSessionsChatWidget.ts) — main wrapper
• AgentSessionsChatTargetConfig (browser/widget/agentSessionsChatTargetConfig.ts) — reactive target state
• AgentSessionsChatWelcomePart (browser/parts/agentSessionsChatWelcomePart.ts) — welcome view
• AgentSessionsChatInputPart (browser/parts/agentSessionsChatInputPart.ts) — standalone input adapter

6. Menus

The agent sessions window uses its own menu IDs defined in browser/menus.ts via the Menus export. Never use shared MenuId.* constants from vs/platform/actions for agent sessions UI — use the Menus.* equivalents instead.

Menu ID	Purpose
Menus.TitleBarLeft	Left toolbar (toggle sidebar)
Menus.TitleBarCenter	Not used directly (see CommandCenter)
Menus.TitleBarRight	Right toolbar (run script, open, toggle auxiliary bar)
Menus.CommandCenter	Center toolbar with session picker widget
Menus.TitleBarControlMenu	Submenu intercepted to render SessionsTitleBarWidget
Menus.PanelTitle	Panel title bar actions
Menus.SidebarTitle	Sidebar title bar actions
Menus.SidebarFooter	Sidebar footer (account widget)
Menus.AuxiliaryBarTitle	Auxiliary bar title actions
Menus.AuxiliaryBarTitleLeft	Auxiliary bar left title actions
Menus.OpenSubMenu	"Open..." split button (Open Terminal, Open in VS Code)
Menus.ChatBarTitle	Chat bar title actions

7. Context Keys

Defined in common/contextkeys.ts:

Context Key	Type	Purpose
activeChatBar	string	ID of the active chat bar panel
chatBarFocus	boolean	Whether chat bar has keyboard focus
chatBarVisible	boolean	Whether chat bar is visible

8. Contributions

Feature contributions live under contrib/<featureName>/browser/ and are registered via imports in sessions.desktop.main.ts (desktop) or sessions.common.main.ts (browser-compatible).

8.1 Key Contributions

Contribution	Location	Purpose
Sessions View	contrib/sessions/browser/	Sessions list in sidebar, session picker, active session service
Title Bar Widget	contrib/sessions/browser/sessionsTitleBarWidget.ts	Session picker in titlebar center
Account Widget	contrib/accountMenu/browser/	Account button in sidebar footer
Run Script	contrib/chat/browser/runScriptAction.ts	Run configured script in terminal
Branch Chat Session	contrib/chat/browser/branchChatSessionAction.ts	Branch a chat session
Open in VS Code / Terminal	contrib/chat/browser/chat.contribution.ts	Open worktree in VS Code or terminal
Prompts Service	contrib/chat/browser/promptsService.ts	Agentic prompts service override
Changes View	contrib/changesView/browser/	File changes in auxiliary bar
AI Customization Editor	contrib/aiCustomizationManagement/browser/	Management editor for prompts, hooks, MCP, etc.
AI Customization Tree	contrib/aiCustomizationTreeView/browser/	Sidebar tree for AI customizations
Configuration	contrib/configuration/browser/	Configuration overrides

8.2 Service Overrides

The agent sessions window registers its own implementations for:

• IPaneCompositePartService → AgenticPaneCompositePartService (creates agent-specific parts)
• IPromptsService → AgenticPromptsService (scopes prompt discovery to active session worktree)
• IActiveSessionService → ActiveSessionService (tracks active session)

8.3 WindowVisibility.Sessions

Views and contributions that should only appear in the agent sessions window (not in regular VS Code) use WindowVisibility.Sessions in their registration.

9. Entry Points

File	Purpose
sessions.common.main.ts	Common entry — imports browser-compatible services, workbench contributions
sessions.desktop.main.ts	Desktop entry — imports desktop services, electron contributions, all contrib/ modules
electron-browser/sessions.main.ts	Desktop bootstrap
electron-browser/sessions.ts	Electron process entry
electron-browser/sessions.html	Production HTML shell
electron-browser/sessions-dev.html	Development HTML shell

10. Development Guidelines

10.1 Adding New Features

1. Core workbench code (layout, parts, services) → browser/
2. Feature contributions (views, actions, editors) → contrib/<featureName>/browser/
3. Register by importing in sessions.desktop.main.ts (or sessions.common.main.ts for browser-compatible)
4. Use Menus.* from browser/menus.ts for menu registrations — never shared MenuId.*
5. Use separate storage keys prefixed with workbench.agentsession.* or workbench.chatbar.*
6. Use agent session part classes, not standard workbench parts
7. Mark views with WindowVisibility.Sessions so they only appear in this window

10.2 Layout Changes

1. Read LAYOUT.md first — it's the authoritative spec
2. Use the agent-sessions-layout skill for detailed implementation guidance
3. Maintain fixed positions — no settings-based customization
4. Update LAYOUT.md and its Revision History after any changes
5. Preserve no-op methods for unsupported features (zen mode, centered layout, etc.)
6. Handle pane composite lifecycle when hiding/showing parts

10.3 Chat Widget Changes

1. Read browser/widget/AGENTS_CHAT_WIDGET.md first
2. Prefer composition over modifying core ChatWidget — add behavior in the wrapper
3. Use IAgentChatTargetConfig observable for target state, not direct session creation
4. Ensure initialSessionOptions travel atomically with the first request
5. Test both first-load (extension not yet activated) and new-session flows

10.4 AI Customization Changes

1. Read AI_CUSTOMIZATIONS.md first — it covers the management editor and tree view design
2. Lean on existing VS Code services (IPromptsService, IMcpService, IChatService)
3. Browser compatibility required — no Node.js APIs
4. Active worktree comes from IActiveSessionService

10.5 Validation

1. Check VS Code - Build task output for compilation errors before declaring work complete
2. Run npm run valid-layers-check for layering violations
3. Verify part visibility toggling (show/hide/maximize)
4. Test editor modal open/close behavior
5. Test sidebar footer renders with account widget