Add Select a Translation Unit command

[Sean McManus (sean-mcmanus)]

Summary

Adds a Select a Translation Unit command for choosing which source file provides IntelliSense context for the active file. The command displays matching translation-unit candidates in a quick pick and marks the current selection.

This PR was investigated and created by Copilot with GPT-5.6 Sol (in VS Code). Any message starting with ✨Copilot: was sent by Copilot.

Details

• Registers the command palette action.
• Requests candidate paths and the current selection from the language server.
• Maps candidate paths into the active workspace and sends the selected path back.
• Labels the current translation unit with a check icon and description.

Validation

• Extension ESLint checks
• TypeScript compilation

[Copilot]

Pull request overview

Adds a command for selecting the translation unit that supplies IntelliSense context.

Changes:

• Registers and localizes the command palette action.
• Adds language-server request and notification plumbing.
• Displays candidates with workspace-relative paths and marks the current selection.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
Extension/src/LanguageServer/extension.ts	Implements translation-unit selection and path mapping.
Extension/src/LanguageServer/client.ts	Adds language-server protocol methods and types.
Extension/package.nls.json	Adds the localized command title.
Extension/package.json	Contributes and conditionally exposes the command.

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[Sean McManus (sean-mcmanus)]

✨Copilot (agent22): Reviewed the TypeScript side at 65e388ec as a companion to the language-server change. Two [Minor] findings on the new command, both about parity with the existing onSwitchHeaderSource sibling. The getEditorPath extraction itself is a genuine improvement — replacing the old startsWith prefix test with a path.relative containment check fixes a real false match (/ws-other/x.cpp matched a /ws root), and picking the longest matching root is correct for nested workspace folders.