Avoidincluding customizations variables into CLI prompt as context

[DonJayamanne]

No description provided.

[Copilot]

Pull request overview

This PR updates Copilot CLI prompt construction to exclude the VS Code “customizations index” prompt reference from the generated prompt context (references/attachments), preventing copilot-instructions–derived customizations from being sent as regular context.

Changes:

• Add a new prompt-variable predicate/constant for identifying the customizations index reference (vscode.customizations.index).
• Filter out the customizations index reference when constructing Copilot CLI prompt references/attachments.
• Add a unit test ensuring the customizations index is excluded while normal file references remain included.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/extension/prompts/node/agent/test/parseAttachments.spec.ts	Adds a test asserting customizations index references/attachments are excluded from the resolved prompt output.
src/extension/prompt/common/chatVariablesCollection.ts	Introduces CustomizationsIndexId and isCustomizationsIndex helper for identifying the special reference.
src/extension/chatSessions/copilotcli/node/copilotcliPromptResolver.ts	Excludes the customizations index from Copilot CLI prompt variable processing.