List of copilot extension jobs in AH

## Summary

Inventory everything the built-in `GitHub.copilot-chat` extension currently does that is relevant to the Agents window, distinguishing extension-backed session providers from features still consumed by Agent Host sessions.

## Extension-backed session providers

These entries include all of their provider-specific support code rather than listing that support separately.

- **Extension-host Copilot CLI sessions** (when enabled)
- Session creation, resume, list, archive, delete, and rename
- SDK lifecycle and model catalog
- Permissions and user questions
- Worktrees, diffs, checkpoints, commit/sync, and pull-request actions
- MCP, agents, skills, instructions, hooks, and plugins
- Copilot CLI terminal integration
- Provider-specific telemetry and OpenTelemetry
- **Extension-host Claude sessions**
- Includes its SDK lifecycle, models, permissions, worktrees, customizations, telemetry, and OpenTelemetry
- **Copilot Cloud sessions**
- Cloud task lifecycle, repository selection, confirmations, interruptions, file changes, pull-request integration, and open-in-browser actions
- **Local VS Code chat sessions**
- Runs the original extension-host Copilot participant/tool-calling agent in the Agents window
- Uses the extension's prompts, tools, model provider, edits, and chat history

## Other Agents-window functionality supplied by the extension

- **Terminal chat and terminal assistance**
- `@terminal` / terminal-panel chat
- Explain Last Command
- Terminal quick fixes
- Terminal commit-message generation
- This is separate from Copilot CLI terminal integration, which belongs under extension-host Copilot CLI sessions.

- **Copilot language-model provider and utility models**
- Publishes the normal Copilot model catalog for extension-host/local-chat functionality.
- Publishes `copilot-utility` and `copilot-utility-small`; the small slot normally resolves to GPT-4o mini.
- Shared UI around Agent Host sessions can still use the utility model for goal-banner summaries, collapsed thinking/tool-group titles, and client-side tool-risk assessment.
- Agent Host now performs its own session/fork titles, branch names, commit messages, and pull-request descriptions through the core Copilot API service; those flows no longer depend on the extension LM provider.

- **BYOK language-model providers**
- OpenAI, Anthropic, Gemini, xAI, Ollama, OpenRouter, Azure, and custom endpoints
- Directly relevant to Agent Host: the Agents window can advertise these models through the BYOK bridge to local or remote Agent Hosts.

- **`toolSearch` Agent Host client tool**
- The extension's edit/read/search/notebook/web tool sets are **not** forwarded wholesale to Agent Host.
- Agent Host advertises only tools in the curated, non-deprecated client-tool sets.
- In the Agents window, the curated sets contain core-owned Automations, Integrated Browser, `runTests`, `testFailure`, `rename`, and `usages`, plus extension-owned `toolSearch`.
- `toolSearch` is therefore the only Copilot-extension tool currently executed directly as an Agent Host client tool. Agent Host exposes it to the model as `tool_search_tool`, then the workbench maps it back to the extension implementation and supplies the host-provided candidate corpus for embedding-based search.

- **GitHub MCP definition provider**
- The extension registers the default `github` MCP server definition and resolves the official GitHub MCP HTTP endpoint.
- Core observes that server through `IMcpService`, bundles eligible non-plugin VS Code MCP servers into the synthetic Agent Host customization plugin, and sends it to Agent Host.
- Core owns Agent Host execution and authentication, including initial reuse of the existing Copilot GitHub token for the official endpoint.

- **`github.copilot.chat.preferLongContext.enabled` compatibility**
- The extension registers this setting; core forwards it to local and remote Agent Hosts.
- For Copilot models with a larger long-context window and no surcharge:
- Off: both Default and Longer Sessions context sizes remain selectable.
- On: the picker is suppressed and Agent Host automatically uses `contextTier: 'long_context'`.
- This is model-configuration compatibility, not a standalone feature.

- **Extension OpenTelemetry status UI in the Agents window**
- The Agents-window status pill invokes extension commands such as `github.copilot.chat.otel.statusActive` and reflects the extension OTel pipeline.
- It does **not** reflect the separate core Agent Host OTel pipeline (`chat.agentHost.otel.*`). This distinction is easy to miss.

## Not direct Agent Host dependencies

- **Extension-host customization providers** are implementation details of extension-host Copilot CLI and Claude sessions. They should remain grouped under those providers.
- Extension manifest prompt files and skills target `local` and/or `copilotcli`, not `agent-host-copilotcli`; they are not the source of Agent Host customizations.
- Agent Host customization discovery/sync and the built-in Agents-window skills such as create PR and merge are core-owned.
- **Extension product telemetry** covers Local chat, extension-host Copilot CLI, extension-host Claude, Cloud, terminal chat, and extension-executed `toolSearch`. Agent Host emits its own product telemetry from the host process, including `agentHost.userMessageSent` and provider-agnostic `languageModelToolInvoked`.
- **Extension OTel** (`github.copilot.chat.otel.*`) covers extension-host/local execution paths. **Agent Host OTel** (`chat.agentHost.otel.*`) is implemented in core and runs in the Agent Host process.

## Practical direct dependencies for Agent Host sessions

If extension-backed session providers and Local chat are considered separately, the remaining direct Copilot-extension dependencies used by Agent Host sessions or their surrounding UI are:

1. Copilot utility language models used by shared client-side UI
2. BYOK language-model providers served through the Agent Host bridge
3. The `toolSearch` client tool
4. The GitHub MCP server definition provider
5. Registration of the prefer-long-context setting
6. The extension OTel status pill integration (UI only; it reports the extension pipeline, not Agent Host OTel)

(Written by Copilot)