MCP Mode Implementation Changes

Overview

Implemented a tri-state MCP mode setting to replace the existing boolean toggle, allowing users to:

Fully enable MCP (including server use and build instructions)
Enable server use only (excluding build instructions to save tokens)
Disable MCP completely

Changes Made

1. Type Definition

Added McpMode type in src/shared/mcp.ts:

export type McpMode = "enabled" | "server-use-only" | "disabled"

2. VSCode Setting

Updated setting definition in package.json:

"cline.mcp.enabled": {
    "type": "string",
    "enum": ["enabled", "server-use-only", "disabled"],
    "enumDescriptions": [
        "Full MCP functionality including server use and build instructions",
        "Enable MCP server use but exclude build instructions from AI prompts to save tokens",
        "Disable all MCP functionality"
    ],
    "default": "enabled",
    "description": "Control MCP server functionality and its inclusion in AI prompts"
}

3. McpHub Changes

Modified src/services/mcp/McpHub.ts:

Removed isMcpEnabled() method
Added getMode(): McpMode method that returns the current mode from VSCode settings

4. Message Types

Updated message types to support the new mode:

In src/shared/WebviewMessage.ts and src/shared/ExtensionMessage.ts:

Added mode?: McpMode property with comment indicating its use with specific message types

5. MCP View Changes

Updated webview-ui/src/components/mcp/McpView.tsx:

Replaced checkbox with dropdown for mode selection
Updated state management to use McpMode type
Added mode-specific descriptions:
- Enabled: "Full MCP functionality including server use and build instructions"
- Server Use Only: "MCP server use is enabled, but build instructions are excluded from AI prompts to save tokens"
- Disabled: Warning about MCP being disabled and token implications
Updated visibility conditions based on mode

6. System Prompt Generation

Added comment in src/core/prompts/system.ts.checks for implementing mode-specific content:

// Mode checks for MCP content:
// - mcpHub.getMode() === "disabled" -> exclude all MCP content
// - mcpHub.getMode() === "server-use-only" -> include server tools/resources but exclude build instructions
// - mcpHub.getMode() === "enabled" -> include all MCP content (tools, resources, and build instructions)

The server building content to be conditionally included (only in "enabled" mode) spans the following sections in system.ts:

Lines 1012-1015: Main section about creating MCP servers
Lines 1017-1021: OAuth and authentication handling
Lines 1025-1392: Example weather server implementation
Lines 1394-1399: Guidelines for modifying existing servers
Lines 1401-1405: Usage notes about when to create vs use existing tools

Next Steps

Implement the system prompt changes using the mode checks provided in system.ts.checks
Test the implementation with all three modes to ensure proper functionality

Testing Required

Verify mode switching in UI works correctly
Confirm proper state persistence
Test system prompt generation with each mode
Verify server connections behave correctly in each mode
Check token usage differences between modes

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