External folder context support (max 3) for monorepos and full-stack workflows

[zamalali]

RFC: External Folders as Context for Copilot Chat

Improve Copilot Chat’s effectiveness across full-stack repos and monorepos by allowing a small, safe set of external folders to be referenced alongside @workspace.

Related: #131429, #155450
Scope: vscode-copilot-chat (no behavior change to existing @workspace or open-file context)

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Problem

@workspace is limited to opened workspace folders. This breaks in common setups:

• Full-stack apps with separate frontend/ and backend/
• Monorepos with shared packages/utils/, packages/types/, etc.

Workarounds today (manual #file drags or reloading the workspace) are clunky and break flow.

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Proposal

New Command

• github.copilot.chat.addExternalContext
  • UI: QuickPick + “Browse for folder…”
  • Adds selected folders as External Context for Copilot Chat.

Limits

• Hard cap: 3 external folders to prevent token bloat.

Prompt Injection

• Inject externals as ChatPromptReference.
• Built-in tools (e.g., listDir, edits) honor them via isExternalPath.

Safeguards

• Exclude noisy/sensitive paths by default:
  • node_modules, .git, dist, binaries
  • Respect files.exclude patterns
• Show warnings for skipped/sensitive paths.

UX

• Status bar badge: $(folder) Contexts: 2/3
• Manage command: github.copilot.chat.manageExternalContexts (remove/edit)

Environment Presets

• Support EXTERNAL_CONTEXT_PATHS to preload paths (devcontainers/CI).

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PoC Summary

Branch: zamalali/vscode-copilot-chat:feat/external-context

• ExternalContextService
  • Manages path set, dedup, events, and the hard cap.
• Integrated with chatParticipantRequestHandler and tooling.
• Tests (vitest)
  • Prompt refs visible
  • Cap enforced
  • Tools read externals
  • Add/remove/events validated
  • Suite passes

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Limitations & Future Work

• No workbench “chips” for externals (closed-source UI). Consider API to expose custom refs.
• Cap may be made configurable later (settings).

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Example Workflow

> github.copilot.chat.addExternalContext
# Choose “Browse for folder…”, then select:
# - packages/utils/
# - packages/types/

# Status bar shows:
$(folder) Contexts: 2/3

# Manage or remove later:
> github.copilot.chat.manageExternalContexts

[alefragnani]

Hi @zamalali ,

If you are not able (or inclined) to open the entire monorepo in VS Code, maybe you could use multi-root workspaces as an alternative, and create one that combines the required projects in it, so @workspace could have the correct context.

Either way, since you are suggesting an improvement to the GitHub Copilot Chat extension, the best place to report this would be the VS Code repo itself (https://github.com/microsoft/vscode/issues), so the team behind the extension could give proper attention to it.

This discussion forum is intended for extension development only, for now.

Hope this helps