VS Code extension — expose open tab list for multi-file context awareness

Problem

<ide_opened_file> only reports the currently focused file in the IDE, not all open tabs. When a user works across 2-3 related files, Claude Code has no visibility into adjacent open tabs and cannot proactively infer cross-file context.

The user must manually switch to each file (triggering <ide_opened_file> updates) before Claude Code becomes aware of those files. This adds friction to cross-file collaboration sessions.

Proposed Solution

Expose the full list of currently open editor tabs in the Claude Code context. This could be:

1. A new <open_tabs> section (preferred) listing all visible tabs, similar to how <project_layout> lists files
2. Or extend <ide_opened_file> to include metadata about other open tabs

Each entry could be minimal — just file path and maybe whether it's dirty or pinned — no need for full file contents.

Use Case

The user has Type.ts, NamedEntity.ts, ClassDefinition.ts, and API_CORE.md open simultaneously. They ask a question that spans all four. Claude Code should see the open-tab list and proactively relate them instead of waiting for the user to switch focus one-by-one.

Implementation Note

Similar data is already available to the extension via VS Code's vscode.window.tabGroups API.