feat: feature configuration service for scope-based toggles

[allenhutchison]

Summary

Implements the Feature Configuration Service from #255, giving users and contributors control over which services and OAuth scopes the extension requests.

• Feature registry (features/feature-config.ts) — 18 read/write feature groups across all services, each declaring its scopes, tools, and default state
• Feature resolver (features/feature-resolver.ts) — Three-layer resolution: baked-in defaults → settings (future) → WORKSPACE_FEATURE_OVERRIDES env var
• Dynamic scopes — OAuth scopes are now computed from enabled features instead of hardcoded
• Gated tool registration — Disabled tools are silently skipped; auth tools always register
• Documentation — Full feature configuration guide added to VitePress docs site

Configuration

# Disable Gmail writes and calendar delete
WORKSPACE_FEATURE_OVERRIDES="gmail.write:off,calendar.deleteEvent:off"

# Enable experimental features
WORKSPACE_FEATURE_OVERRIDES="slides.write:on,tasks.read:on,tasks.write:on"

Supports group-level (gmail.write:off) and tool-level (calendar.deleteEvent:off) overrides. Tool-level overrides are subtractive only.

Default-OFF features

slides.write, sheets.write, tasks.read, tasks.write — scopes not in the published GCP project. Contributors can enable them with their own GCP projects.

Test plan

• 23 new unit tests covering registry integrity, override parsing, group enable/disable, tool-level overrides, subtractive-only enforcement, layer precedence, and scope deduplication
• Manual: verify WORKSPACE_FEATURE_OVERRIDES="gmail.write:off" hides Gmail write tools from MCP tool listing
• Manual: verify re-enabling a disabled feature prompts re-auth for new scopes
• Manual: verify no behavior change when env var is unset (backward compatible)

Closes #255

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a comprehensive feature configuration service, providing granular control over services and OAuth scopes. It enhances the extension's adaptability and security by dynamically computing scopes and gating tool registration based on user-defined settings and environment variables. The changes include a feature registry, a feature resolver, and updated documentation to guide users and contributors.

Highlights

• Feature Configuration Service: This PR implements a feature configuration service that allows users and contributors to control which services and OAuth scopes the extension requests, enhancing flexibility and security.
• Dynamic Scopes: OAuth scopes are now computed dynamically based on enabled features, rather than being hardcoded, providing a more adaptive permission system.
• Tool Registration Gating: The registration of tools is now gated, with disabled tools being silently skipped, ensuring that only enabled features are exposed and auth tools are always registered.
• Configuration Flexibility: Introduces a three-layer resolution for feature settings: baked-in defaults, settings (future), and WORKSPACE_FEATURE_OVERRIDES environment variable, offering multiple configuration options.

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[gemini-code-assist]

Code Review

This pull request introduces a comprehensive feature configuration service, enabling dynamic control over which services and OAuth scopes the extension requests. The implementation includes a well-structured feature registry (feature-config.ts), a robust resolver (feature-resolver.ts) with a three-layer precedence model (defaults, settings, environment variables), and dynamic OAuth scope computation. The changes also correctly gate tool registration based on the enabled features, with a sensible exception for authentication tools. Extensive unit tests have been added for both the feature configuration and resolver logic, ensuring correctness and reliability. Documentation has been updated to reflect these new configuration capabilities, providing clear guidance for users and contributors. Overall, this is a well-designed and thoroughly implemented feature that significantly enhances the flexibility and maintainability of the extension.