Chat Customizations Editor

# Chat Customizations Editor

Split-view management pane for AI customization items across workspace, user, extension, and plugin storage. Supports harness-based filtering (Local, Copilot CLI, Claude).

## Spec

**`src/vs/sessions/AI_CUSTOMIZATIONS.md`** — always read before making changes, always update after.

## Key Folders

| Folder | What |
|--------|------|
| `src/vs/workbench/contrib/chat/common/` | `ICustomizationHarnessService`, `ISectionOverride`, `IStorageSourceFilter` — shared interfaces and filter helpers |
| `src/vs/workbench/contrib/chat/browser/aiCustomization/` | Management editor, list widgets (prompts, MCP, plugins), harness service registration |
| `src/vs/sessions/contrib/chat/browser/` | Sessions-window overrides (harness service, workspace service) |
| `src/vs/sessions/contrib/sessions/browser/` | Sessions tree view counts and toolbar |

When changing harness descriptor interfaces or factory functions, verify both core and sessions registrations compile.

## Key Interfaces

- **`IHarnessDescriptor`** — drives all UI behavior declaratively (hidden sections, button overrides, file filters, agent gating). See spec for full field reference.
- **`ISectionOverride`** — per-section button customization (command invocation, root file creation, type labels, file extensions).
- **`IStorageSourceFilter`** — controls which storage sources and user roots are visible per harness/type.
- **`IExternalCustomizationItemProvider`** / **`IExternalCustomizationItem`** — internal interfaces (in `customizationHarnessService.ts`) for extension-contributed providers that supply items directly. These mirror the proposed extension API types.

Principle: the UI widgets read everything from the descriptor — no harness-specific conditionals in widget code.

## Extension API (`chatSessionCustomizationProvider`)

The proposed API in `src/vscode-dts/vscode.proposed.chatSessionCustomizationProvider.d.ts` lets extensions register customization providers. Changes to `IExternalCustomizationItem` or `IExternalCustomizationItemProvider` must be kept in sync across the full chain:

| Layer | File | Type |
|-------|------|------|
| Extension API | `vscode.proposed.chatSessionCustomizationProvider.d.ts` | `ChatSessionCustomizationItem` |
| IPC DTO | `extHost.protocol.ts` | `IChatSessionCustomizationItemDto` |
| ExtHost mapping | `extHostChatAgents2.ts` | `$provideChatSessionCustomizations()` |
| MainThread mapping | `mainThreadChatAgents2.ts` | `provideChatSessionCustomizations` callback |
| Internal interface | `customizationHarnessService.ts` | `IExternalCustomizationItem` |

When adding fields to `IExternalCustomizationItem`, update all five layers. The proposed API `.d.ts` is additive-only (new optional fields are backward-compatible and do not require a version bump).

## Testing

Component explorer fixtures (see `component-fixtures` skill): `aiCustomizationListWidget.fixture.ts`, `aiCustomizationManagementEditor.fixture.ts` under `src/vs/workbench/test/browser/componentFixtures/`.

### Screenshotting specific tabs

The management editor fixture supports a `selectedSection` option to render any tab. Each tab has Dark/Light variants auto-generated by `defineThemedFixtureGroup`.

**Available fixture IDs** (use with `mcp_component-exp_screenshot`):

| Fixture ID pattern | Tab shown |
|---|---|
| `chat/aiCustomizations/aiCustomizationManagementEditor/AgentsTab/{Dark,Light}` | Agents |
| `chat/aiCustomizations/aiCustomizationManagementEditor/SkillsTab/{Dark,Light}` | Skills |
| `chat/aiCustomizations/aiCustomizationManagementEditor/InstructionsTab/{Dark,Light}` | Instructions |
| `chat/aiCustomizations/aiCustomizationManagementEditor/HooksTab/{Dark,Light}` | Hooks |
| `chat/aiCustomizations/ai