[Repo Assist] perf: replace map[string]interface{} with typed structs in RPC hot paths

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Summary

Replaces map[string]interface{} allocations on the JSON-RPC request hot path with typed structs, reducing per-call heap allocations and GC pressure.

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Changes

internal/mcp/http_transport.go — createJSONRPCRequest

Every outbound HTTP JSON-RPC request called createJSONRPCRequest, which allocated a map[string]interface{} just to marshal it into JSON bytes immediately afterward. Go maps always live on the heap (the internal hash table is heap-allocated), even for tiny maps with 4 entries.

Replaced with:

type jsonrpcRequest struct {
    JSONRPC string      `json:"jsonrpc"`
    ID      uint64      `json:"id"`
    Method  string      `json:"method"`
    Params  interface{} `json:"params"`
}

internal/mcp/connection.go — SendRequestWithServerID

The outbound request log entry also built a map[string]interface{} on every call (for stdio and HTTP connections alike). Replaced with a dedicated jsonrpcLogPayload struct (no ID field since the log format doesn't include it).

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Why It Helps

• No map hash table allocation — struct values can be stack-allocated or inlined by the compiler; maps always escape to heap
• Faster JSON marshaling — struct marshaling uses pre-computed field offsets and skips the map key type-assertion loop
• Same wire format — encoding/json produces identical JSON output from both representations

For an MCP gateway that proxies every tool call through these paths, eliminating 2 heap allocations per request reduces GC frequency under load.

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Tests Updated

TestCreateJSONRPCRequest and TestCreateJSONRPCRequest_HasAllRequiredFields updated to use struct field access (req.JSONRPC, req.ID, etc.) instead of map key lookups. TestCreateJSONRPCRequest_IsSerializable was unchanged (it round-trips through JSON).

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Test Status

Infrastructure note: the Go module proxy is blocked in this agent environment (network firewall). Module cache is empty so go test cannot compile. The changes are structurally sound (correct JSON tags, consistent field types); CI will run the full test suite.

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