Assessment: 🟢 APPROVE

The PR cleanly introduces a configurable standaloneSSE flag on remoteMCPClient and exposes it through Toolset.SetStandaloneSSE. The implementation is correct:

• c.mu is sync.RWMutex (embedded from sessionClient), so c.mu.RLock() / c.mu.RUnlock() in Initialize compiles correctly and is consistent with existing usage throughout session_client.go.
• The type assertion on ts.mcpClient in Toolset.SetStandaloneSSE without holding ts.mu is safe — mcpClient is set in the constructor and never reassigned, matching the same pattern already used in Kind() and WorkingDir().
• SetStandaloneSSE uses a write lock (c.mu.Lock()) while Initialize uses a read lock to snapshot the field — correct reader/writer separation.
• Defaulting to false (standalone SSE disabled) preserves backward compatibility.