Agents window should show and continue local Copilot Chat Agent sessions

The Agents window documentation says the Agents window and the Chat view share the same agent sessions and settings, so users can move between an editor-focused workflow and an agent-focused workflow without losing context.

From the user side, the current behavior still feels split: normal local Copilot Agent sessions started from the Chat view/sidebar are not clearly visible or continuable in the Agents window. The Agents window appears centered on Copilot CLI, Copilot Cloud, and third-party agent-host sessions, while the Chat view's native/local Copilot Agent experience remains separate.

Expected:

* A local Copilot Agent session started in the Chat view/sidebar can be found, opened, and continued in the Agents window.
* A compatible session started in the Agents window can be found and continued from the Chat view where appropriate.
* If local/workbench Copilot Agent sessions are intentionally not supported in the Agents window yet, the UI and docs should make that distinction clear.

Why this matters:

The Chat view's local Copilot Agent has the native VS Code experience: workbench context, VS Code tools, extension-provided tools, MCP/model configuration, and integrated terminal behavior. The Agents window is useful for cross-project orchestration, but if it only supports different session backends, users have to choose between the native agent experience and the new agent-focused session manager.

Related issues:

* #319415 tracks Copilot CLI sessions appearing in the regular Chat Sessions panel but not in the Agents window.
* #317895 tracks MCP configuration and BYOK model parity gaps for the Agents window local agent.
* #323969 tracks session-reference attachment support across chat/session types.
* #323970 tracks full session porting for Continue in Agent Host, including local/workbench chat sessions.

This is filed as a user-facing integration gap rather than a request for a specific implementation. The important outcome is that the normal Copilot Agent experience in the Chat view and the new Agents window do not feel like separate products with separate histories.