Sessions

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.

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

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

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.

7. Context Keys

Defined in common/contextkeys.ts:

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

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

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