fix(mcp): remove client-side cache and reduce server cache from 5m to 30s - #2182

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Project	Deployment	Preview	Comments	Updated (UTC)
docs	Skipped			Dec 4, 2025 4:50pm

Greptile Overview

Greptile Summary

This PR reverts to a stateless connection model by removing session ID caching and reducing server-side tool cache from 5 minutes to 30 seconds.

Key Changes:

• Removed sessionId parameter from McpClient constructor - connections now disconnect after each operation
• Removed session caching logic (sessionCache Map and related methods) from McpService
• Reduced CACHE_TIMEOUT constant from 5 minutes to 30 seconds
• Added intelligent cache-skipping logic - if any server fails during tool discovery, the result is not cached (will retry on next request)
• Improved logging to show success/failure ratio for multi-server tool discovery

Impact:

• Simplified architecture by removing session management complexity
• Shorter cache duration means fresher data but potentially more server requests
• Better error recovery through cache-skipping on partial failures

Confidence Score: 4/5

• This PR is safe to merge with minor style improvements recommended
• The changes successfully simplify the MCP connection architecture by removing session management. The logic is sound and includes good error handling (cache-skipping on failures). Minor issues: (1) hardcoded cache timeout instead of using constant creates inconsistency, (2) unused getSessionId() method remains as dead code. These are style issues that don't affect functionality.
• Pay attention to apps/sim/lib/mcp/service.ts for cache timeout constant usage

Important Files Changed

File Analysis

Sequence Diagram

sequenceDiagram
    participant Client as Frontend
    participant API as API Route
    participant Service as McpService
    participant McpClient as McpClient
    participant Server as MCP Server

    Note over Service: Server-side cache: 30s

    Client->>API: Request tools/execute
    API->>Service: discoverTools() or executeTool()
    
    alt Cache hit (< 30s)
        Service-->>API: Return cached tools
        API-->>Client: Response
    else Cache miss or expired
        Service->>McpClient: new McpClient(config)
        Note over McpClient: No sessionId parameter
        McpClient->>Server: connect()
        Server-->>McpClient: Session established (SDK manages sessionId)
        McpClient->>Server: listTools() or callTool()
        Server-->>McpClient: Response
        McpClient->>Server: disconnect()
        Note over McpClient: Connection closed after operation
        McpClient-->>Service: Result
        
        alt All servers succeeded
            Service->>Service: Cache result (30s)
        else Any server failed
            Note over Service: Skip caching to retry next time
        end
        
        Service-->>API: Result
        API-->>Client: Response
    end