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.github/instructions/ai-customization.instructions.md

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+---
+description: Architecture documentation for VS Code AI Customization view. Use when working in `src/vs/workbench/contrib/chat/browser/aiCustomization`
+applyTo: 'src/vs/workbench/contrib/chat/browser/aiCustomization/**'
+---
+
+# AI Customization View
+
+The AI Customization view provides a unified view for discovering and managing AI customization 'artifacts' (customizations that augment LLM prompts or behavior).
+
+Examples of these include: Custom Agents, Skills, Instructions, and Prompts. It surfaces prompt files that are typically hidden in `.github/` folders, user data directories, workspace settings, or exposed via extensions.
+
+## Overview
+
+The view displays a hierarchical tree structure:
+
+```
+AI Customization (View Container)
+└── AI Customization (Tree View)
+    ├── Custom Agents (.agent.md files)
+    │   ├── Workspace
+    │   │   └── agent files...
+    │   ├── User
+    │   │   └── agent files...
+    │   └── Extensions
+    │       └── agent files...
+    ├── Skills (SKILL.md files)
+    │   └── (same storage structure)
+    ├── Instructions (.instructions.md files)
+    │   └── (same storage structure)
+    └── Prompts (.prompt.md files)
+        └── (same storage structure)
+```
+
+**Key Features:**
+- 3-level tree hierarchy: Category → Storage Group → Files
+- Auto-expands category nodes on initial load and refresh to show storage groups
+- Symbol-based root element for type safety
+- Double-click to open files in editor
+- Context menu support with Open and Run Prompt actions
+- Toolbar actions: New dropdown, Refresh, Collapse All
+- Skill names parsed from frontmatter with fallback to folder name
+- Responsive to IPromptsService change events
+
+## File Structure
+
+All files are located in `src/vs/workbench/contrib/chat/browser/aiCustomization/`:
+
+```
+aiCustomization/
+├── aiCustomization.ts              # Constants, IDs, and MenuIds
+├── aiCustomization.contribution.ts # View registration and actions
+├── aiCustomizationViews.ts         # Tree view pane implementation
+├── aiCustomizationIcons.ts         # Icon registrations
+└── media/
+    └── aiCustomization.css         # Styling
+```
+
+## Key Constants (aiCustomization.ts)
+
+- `AI_CUSTOMIZATION_VIEWLET_ID`: View container ID for sidebar
+- `AI_CUSTOMIZATION_VIEW_ID`: Unified tree view ID
+- `AI_CUSTOMIZATION_STORAGE_ID`: State persistence key
+- `AICustomizationItemMenuId`: Context menu ID
+- `AICustomizationNewMenuId`: New item submenu ID
+
+## View Registration (aiCustomization.contribution.ts)
+
+### View Container
+
+Register sidebar container with:
+- ViewPaneContainer with `mergeViewWithContainerWhenSingleView: true`
+- Keyboard shortcut: Cmd+Shift+I
+- Location: Sidebar
+- Visibility: `when: ChatContextKeys.enabled` (respects AI disable setting)
+
+### View Descriptor
+
+Register single unified tree view:
+- Constructor: `AICustomizationViewPane`
+- Toggleable and moveable
+- Gated by `ChatContextKeys.enabled`
+
+### Welcome Content
+
+Shows markdown links to create new items when tree is empty.
+
+## Toolbar Actions
+
+**New Item Dropdown** - Submenu in view title:
+- Add icon in navigation group
+- Submenu contains: New Agent, New Skill, New Instructions, New Prompt
+- Each opens PromptFilePickers to guide user through creation
+
+**Refresh** - ViewAction that calls `view.refresh()`
+
+**Collapse All** - ViewAction that calls `view.collapseAll()`
+
+All actions use `ViewAction<AICustomizationViewPane>` pattern and are gated by `when: view === AI_CUSTOMIZATION_VIEW_ID`.
+
+## Tree View Implementation (aiCustomizationViews.ts)
+
+### Tree Item Types
+
+Discriminated union with `type` field:
+
+**ROOT_ELEMENT** - Symbol marker for type-safe root
+
+**IAICustomizationTypeItem** (`type: 'category'`)
+- Represents: Custom Agents, Skills, Instructions, Prompts
+- Contains: label, promptType, icon
+
+**IAICustomizationGroupItem** (`type: 'group'`)
+- Represents: Workspace, User, Extensions
+- Contains: label, storage, promptType, icon
+
+**IAICustomizationFileItem** (`type: 'file'`)
+- Represents: Individual prompt files
+- Contains: uri, name, description, storage, promptType
+
+### Data Source
+
+`UnifiedAICustomizationDataSource` implements `IAsyncDataSource`:
+
+**getChildren logic:**
+- ROOT → 4 categories (agent, skill, instructions, prompt)
+- category → storage groups (workspace, user, extensions) that have items
+- group → files from `promptsService.listPromptFilesForStorage()` or `findAgentSkills()`
+
+**Skills special handling:** Uses `findAgentSkills()` to get names from frontmatter instead of filenames
+
+### Tree Renderers
+
+Three specialized renderers for category/group/file items:
+- **Category**: Icon + bold label
+- **Group**: Uppercase label with descriptionForeground color
+- **File**: Icon + name with tooltip
+
+### View Pane
+
+`AICustomizationViewPane extends ViewPane`:
+
+**Injected services:**
+- IPromptsService - data source
+- IEditorService - open files
+- IMenuService - context menus
+
+**Initialization:**
+1. Subscribe to `onDidChangeCustomAgents` and `onDidChangeSlashCommands` events
+2. Create WorkbenchAsyncDataTree with 3 renderers and data source
+3. Register handlers: `onDidOpen` (double-click) → open file, `onContextMenu` → show menu
+4. Set input to ROOT_ELEMENT and auto-expand categories
+
+**Auto-expansion:**
+- After setInput, iterate root children and expand each category
+- Reveals storage groups without user interaction
+- Applied on both initial load and refresh
+
+**Public API:**
+- `refresh()` - Reload tree and re-expand categories
+- `collapseAll()` - Collapse all nodes
+- `expandAll()` - Expand all nodes
+
+## Context Menu Actions
+
+Menu ID: `AICustomizationItemMenuId`
+
+**Actions:**
+- **Open** - Opens file in editor using IEditorService
+- **Run Prompt** - Only for prompt files, invokes chat with prompt
+
+**URI handling:** Actions must handle both URI objects and serialized strings
+- Check `URI.isUri(context)` first
+- Parse string variants with `URI.parse()`
+
+**Context passing:**
+- Serialize context as `{ uri: string, name: string, promptType: PromptsType }`
+- Use `shouldForwardArgs: true` in getMenuActions
+- Only show context menu for file items (not categories/groups)
+
+## Icons (aiCustomizationIcons.ts)
+
+Themed icons using `registerIcon(id, codicon, label)`:
+
+**View/Types:**
+- aiCustomizationViewIcon - Codicon.sparkle
+- agentIcon - Codicon.copilot
+- skillIcon - Codicon.lightbulb
+- instructionsIcon - Codicon.book
+- promptIcon - Codicon.bookmark
+
+**Storage:**
+- workspaceIcon - Codicon.folder
+- userIcon - Codicon.account
+- extensionIcon - Codicon.extensions
+
+## Styling (media/aiCustomization.css)
+
+**Layout:** Full height view and tree container
+
+**Tree items:** Flex layout with 16px icon + text, ellipsis overflow
+
+**Categories:** Bold font-weight
+
+**Groups:** Uppercase, small font (11px), letter-spacing, descriptionForeground color
+
+## Integration Points
+
+**IPromptsService:**
+- `listPromptFilesForStorage(type, storage)` - Get files for a type/storage combo
+- `findAgentSkills()` - Get skills with names parsed from frontmatter
+- `onDidChangeCustomAgents` - Refresh on agent changes
+- `onDidChangeSlashCommands` - Refresh on command changes
+
+**PromptsType enum:** `instructions | prompt | agent | skill`
+
+**PromptsStorage enum:** `local` (workspace) | `user` | `extension`
+
+**AI Feature Gating:** View gated by `ChatContextKeys.enabled` (respects `chat.disableAIFeatures` setting)
+
+**Registration:** Import `./aiCustomization/aiCustomization.contribution.js` in `chat.contribution.ts`
+
+---
+
+*Update this file when making architectural changes to the AI Customization view.*

.github/instructions/sessions.instructions.md

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+---
+description: Architecture documentation for the Agent Sessions window — a sessions-first app built as a new top-level layer alongside vs/workbench. Covers layout, parts, chat widget, contributions, entry points, and development guidelines. Use when working in `src/vs/sessions`
+applyTo: src/vs/sessions/**
+---
+
+# Agent Sessions Window
+
+The Agent Sessions window is a **standalone application** built as a new top-level layer (`vs/sessions`) in the VS Code architecture. It provides a sessions-first experience optimized for agent workflows — a simplified, fixed-layout workbench where chat is the primary interaction surface and editors appear as modal overlays.
+
+When working on files under `src/vs/sessions/`, use these skills for detailed guidance:
+
+- **`sessions`** skill — covers the full architecture: layering, folder structure, chat widget, menus, contributions, entry points, and development guidelines
+- **`agent-sessions-layout`** skill — covers the fixed layout structure, grid configuration, part visibility, editor modal, titlebar, sidebar footer, and implementation requirements

.github/skills/agent-sessions-layout/SKILL.md

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+---
+name: agent-sessions-layout
+description: Agent Sessions workbench layout — covers the fixed layout structure, grid configuration, part visibility, editor modal, titlebar, sidebar footer, and implementation requirements. Use when implementing features or fixing issues in the Agent Sessions workbench layout.
+---
+
+When working on the Agent Sessions workbench layout, always follow these guidelines:
+
+## 1. Read the Specification First
+
+The authoritative specification for the Agent Sessions layout lives at:
+
+**`src/vs/sessions/LAYOUT.md`**
+
+Before making any changes to the layout code, read and understand the current spec. It defines:
+
+- The fixed layout structure (grid tree, part positions, default sizes)
+- Which parts are included/excluded and their visibility defaults
+- Titlebar configuration and custom menu IDs
+- Editor modal overlay behavior and sizing
+- Part visibility API and events
+- Agent session part classes and storage keys
+- Workbench contributions and lifecycle
+- CSS classes and file structure
+
+## 2. Keep the Spec in Sync
+
+If you modify the layout implementation, you **must** update `LAYOUT.md` to reflect those changes. The spec should always match the code. This includes:
+
+- Adding/removing parts or changing their positions
+- Changing default visibility or sizing
+- Adding new actions, menus, or contributions
+- Modifying the grid structure
+- Changing titlebar configuration
+- Adding new CSS classes or file structure changes
+
+Update the **Revision History** table at the bottom of `LAYOUT.md` with a dated entry describing what changed.
+
+## 3. Implementation Principles
+
+When proposing or implementing changes, follow these rules from the spec:
+
+1. **Maintain fixed positions** — Do not add settings-based position customization
+2. **Panel must span the right section width** — The grid structure places the panel below Chat Bar and Auxiliary Bar only
+3. **Sidebar spans full height** — Sidebar is in the main content branch, spanning from top to bottom
+4. **New parts go in the right section** — Any new parts should be added to the horizontal branch alongside Chat Bar and Auxiliary Bar
+5. **Preserve no-op methods** — Unsupported features (zen mode, centered layout, etc.) should remain as no-ops, not throw errors
+6. **Handle pane composite lifecycle** — When hiding/showing parts, manage the associated pane composites
+7. **Use agent session parts** — New part functionality goes in the agent session part classes (`SidebarPart`, `AuxiliaryBarPart`, `PanelPart`, `ChatBarPart`), not the standard workbench parts
+8. **Use separate storage keys** — Agent session parts use their own storage keys (prefixed with `workbench.agentsession.` or `workbench.chatbar.`) to avoid conflicts with regular workbench state
+9. **Use agent session menu IDs** — Actions should use `Menus.*` menu IDs (from `sessions/browser/menus.ts`), not shared `MenuId.*` constants
+
+## 4. Key Files
+
+| File | Purpose |
+|------|---------|
+| `sessions/LAYOUT.md` | Authoritative specification |
+| `sessions/browser/workbench.ts` | Main layout implementation (`Workbench` class) |
+| `sessions/browser/menus.ts` | Agent sessions menu IDs (`Menus` export) |
+| `sessions/browser/layoutActions.ts` | Layout actions (toggle sidebar, panel, secondary sidebar) |
+| `sessions/browser/paneCompositePartService.ts` | `AgenticPaneCompositePartService` |
+| `sessions/browser/style.css` | Layout-specific styles |
+| `sessions/browser/parts/` | Agent session part implementations |
+| `sessions/browser/parts/titlebarPart.ts` | Titlebar part, MainTitlebarPart, AuxiliaryTitlebarPart, TitleService |
+| `sessions/browser/parts/editorModal.ts` | Editor modal overlay |
+| `sessions/browser/parts/sidebarPart.ts` | Sidebar part (with footer) |
+| `sessions/browser/parts/chatBarPart.ts` | Chat Bar part |
+| `sessions/browser/widget/` | Agent sessions chat widget |
+| `sessions/contrib/sessions/browser/sessionsTitleBarWidget.ts` | Title bar widget and session picker |
+| `sessions/contrib/chat/browser/runScriptAction.ts` | Run script contribution |
+| `sessions/contrib/accountMenu/browser/account.contribution.ts` | Account widget for sidebar footer |
+
+## 5. Testing Changes
+
+After modifying layout code:
+
+1. Verify the build compiles without errors via the `VS Code - Build` task
+2. Ensure the grid structure matches the spec's visual representation
+3. Confirm part visibility toggling works correctly (show/hide/maximize)
+4. Test the editor modal opens/closes properly on editor events
+5. Verify sidebar footer renders with account widget