| name | sessions |
| description | Agents window architecture — covers the agents-first app, layering, folder structure, chat widget, menus, contributions, entry points, and development guidelines. Use when implementing features or fixing issues in the Agents window. |
When working on the Agents 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 |
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 | Agents 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 | Agent 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, context keys, and theme
│ ├── categories.ts # Command categories
│ ├── contextkeys.ts # ChatBar and welcome context keys
│ └── theme.ts # Theme contributions
├── 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
│ ├── widget/ # Agent sessions chat widget
│ │ └── AGENTS_CHAT_WIDGET.md # Chat widget architecture doc
│ ├── 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
│ │ ├── panelPart.ts # Panel (terminal, output, etc.)
│ │ ├── projectBarPart.ts # Project bar (folder entries)
│ │ └── media/ # Part CSS files
│ └── media/ # Layout-specific styles
├── 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
│ ├── titleService.ts # Desktop title service override
│ └── parts/
│ └── titlebarPart.ts # Desktop titlebar part
├── services/ # Service overrides
│ ├── configuration/browser/ # Configuration service overrides
│ └── workspace/browser/ # Workspace service overrides
├── test/ # Unit tests
│ └── browser/
│ └── layoutActions.test.ts
└── contrib/ # Feature contributions
├── accountMenu/browser/ # Account widget for sidebar footer
├── agentFeedback/browser/ # Agent feedback attachments, overlays, hover
├── aiCustomizationTreeView/browser/ # AI customization tree view sidebar
├── applyToParentRepo/browser/ # Apply changes to parent repo
├── changesView/browser/ # File changes view
├── chat/browser/ # Chat actions (run script, branch, prompts)
├── configuration/browser/ # Configuration overrides
├── files/browser/ # File-related contributions
├── fileTreeView/browser/ # File tree view (filesystem provider)
├── gitSync/browser/ # Git sync contributions
├── logs/browser/ # Log contributions
├── sessions/browser/ # Sessions view, title bar widget, active session service
├── terminal/browser/ # Terminal contributions
├── welcome/browser/ # Welcome view contribution
└── workspace/browser/ # Workspace contributions
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 Agents 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 wrapperAgentSessionsChatTargetConfig (browser/widget/agentSessionsChatTargetConfig.ts) — reactive target stateAgentSessionsChatWelcomePart (browser/parts/agentSessionsChatWelcomePart.ts) — welcome viewAgentSessionsChatInputPart (browser/parts/agentSessionsChatInputPart.ts) — standalone input adapter
6. Menus
The agents 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 agents window UI — use the Menus.* equivalents instead.
| Menu ID | Purpose |
|---|
Menus.ChatBarTitle | Chat bar title actions |
Menus.CommandCenter | Center toolbar with agent picker widget |
Menus.CommandCenterCenter | Center section of command center |
Menus.TitleBarContext | Titlebar context menu |
Menus.TitleBarLeftLayout | Left layout toolbar |
Menus.TitleBarSessionTitle | Agent title in titlebar |
Menus.TitleBarSessionMenu | Agent menu in titlebar |
Menus.TitleBarRightLayout | Right layout toolbar |
Menus.PanelTitle | Panel title bar actions |
Menus.SidebarTitle | Sidebar title bar actions |
Menus.SidebarFooter | Sidebar footer (account widget) |
Menus.SidebarCustomizations | Sidebar customizations menu |
Menus.AuxiliaryBarTitle | Auxiliary bar title actions |
Menus.AuxiliaryBarTitleLeft | Auxiliary bar left title actions |
Menus.AgentFeedbackEditorContent | Agent feedback editor content menu |
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 |
sessionsWelcomeVisible | boolean | Whether the agents welcome overlay 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/ | Agents list in sidebar, agent picker, active session service |
| Title Bar Widget | contrib/sessions/browser/sessionsTitleBarWidget.ts | Agent picker in titlebar center |
| Account Widget | contrib/accountMenu/browser/ | Account button in sidebar footer |
| Chat Actions | contrib/chat/browser/ | Chat actions (run script, branch, prompts, customizations debug log) |
| Changes View | contrib/changesView/browser/ | File changes in auxiliary bar |
| Agent Feedback | contrib/agentFeedback/browser/ | Agent feedback attachments, editor overlays, hover |
| AI Customization Tree | contrib/aiCustomizationTreeView/browser/ | Sidebar tree for AI customizations |
| Apply to Parent Repo | contrib/applyToParentRepo/browser/ | Apply changes to parent repo |
| Files | contrib/files/browser/ | File-related contributions |
| File Tree View | contrib/fileTreeView/browser/ | File tree view (filesystem provider) |
| Git Sync | contrib/gitSync/browser/ | Git sync contributions |
| Logs | contrib/logs/browser/ | Log contributions |
| Terminal | contrib/terminal/browser/ | Terminal contributions |
| Welcome | contrib/welcome/browser/ | Welcome view contribution |
| Workspace | contrib/workspace/browser/ | Workspace contributions |
| Configuration | contrib/configuration/browser/ | Configuration overrides |
8.2 Service Overrides
The agents 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)
Service overrides also live under services/:
services/configuration/browser/ - configuration service overridesservices/workspace/browser/ - workspace service overrides
8.3 WindowVisibility.Sessions
Views and contributions that should only appear in the agents 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 |
electron-browser/titleService.ts | Desktop title service override |
electron-browser/parts/titlebarPart.ts | Desktop titlebar part |
10. Development Guidelines
10.1 Adding New Features
- Core workbench code (layout, parts, services) →
browser/
- Feature contributions (views, actions, editors) →
contrib/<featureName>/browser/
- Register by importing in
sessions.desktop.main.ts (or sessions.common.main.ts for browser-compatible)
- Use
Menus.* from browser/menus.ts for menu registrations — never shared MenuId.*
- Use separate storage keys prefixed with
workbench.agentsession.* or workbench.chatbar.*
- Use agent session part classes, not standard workbench parts
- Mark views with
WindowVisibility.Sessions so they only appear in this window
10.2 Validating Changes
- Run
npm run compile-check-ts-native to run a repo-wide TypeScript compilation check (including src/vs/sessions/). This is a fast way to catch TypeScript errors introduced by your changes.
- Run
npm run valid-layers-check to verify layering rules are not violated.
- Use
scripts/test.sh (or scripts\test.bat on Windows) for unit tests (add --grep <pattern> to filter tests)
Important do not run tsc to check for TypeScript errors always use above methods to validate TypeScript changes in src/vs/**.
10.3 Layout Changes
- Read
LAYOUT.md first — it's the authoritative spec
- Use the
agent-sessions-layout skill for detailed implementation guidance
- Maintain fixed positions — no settings-based customization
- Update
LAYOUT.md and its Revision History after any changes
- Preserve no-op methods for unsupported features (zen mode, centered layout, etc.)
- Handle pane composite lifecycle when hiding/showing parts
10.3 Chat Widget Changes
- Read
browser/widget/AGENTS_CHAT_WIDGET.md first
- Prefer composition over modifying core
ChatWidget — add behavior in the wrapper
- Use
IAgentChatTargetConfig observable for target state, not direct session creation
- Ensure
initialSessionOptions travel atomically with the first request
- Test both first-load (extension not yet activated) and new-session flows
10.4 AI Customization Changes
- Read
AI_CUSTOMIZATIONS.md first — it covers the management editor and tree view design
- Lean on existing VS Code services (
IPromptsService, IMcpService, IChatService)
- Browser compatibility required — no Node.js APIs
- Active worktree comes from
IActiveSessionService
10.5 Validation
- Check
VS Code - Build task output for compilation errors before declaring work complete
- Run
npm run valid-layers-check for layering violations
- Verify part visibility toggling (show/hide/maximize)
- Test editor modal open/close behavior
- Test sidebar footer renders with account widget
