Refactor HTTP transport auth helpers and simplify sys/tracing boundaries

[Copilot]

This PR addresses four carry-over refactoring items from the semantic clustering analysis plus the dead SysServer routing path. The goal is to tighten file boundaries so transport auth, session lifecycle, tracing parent-context construction, and sys tool dispatch each live with their actual responsibilities.

• HTTP transport auth/client split

  • Moved the HTTP client/auth construction layer out of internal/mcp/http_transport.go into internal/mcp/http_transport_client.go
  • Isolates:
    • newMCPClient
    • headerInjectingRoundTripper
    • buildHTTPClientWithHeaders
    • oidcRoundTripper
    • buildHTTPClientWithOIDC
  • Leaves http_transport.go focused on negotiation, parsing, request execution, and session handling

• Sys tool session lifecycle moved to session.go

  • Extracted the inline sys___init / sys___list_servers closures from internal/server/tool_registry.go
  • Added named UnifiedServer methods in internal/server/session.go:
    • sysInitHandler
    • sysListServersHandler
  • Consolidates session creation, session validation, and payload-directory setup with the rest of the session lifecycle code

• Tracing ParentContext inlined at the public API

  • Moved the full parent-context construction logic into internal/tracing/provider.go:ParentContext
  • Removed the extra forwarding layer from internal/tracing/config_resolver.go
  • Keeps the exported tracing API and its implementation in one place

• Dead SysServer request router removed

  • Simplified internal/server/system_tools.go to direct methods:
    • SysInit()
    • ListServers()
  • Removed the unused HandleRequest("tools/list" | "tools/call") abstraction and the dead tools/list production branch
  • Updated callSysServer to dispatch directly to SysServer methods

• Focused test updates

  • Reworked sys tool tests to cover direct SysInit / ListServers behavior instead of the removed router
  • Added session-handler coverage for the extracted sysInitHandler and sysListServersHandler
  • Kept existing HTTP transport and tracing coverage aligned with the refactor

Example of the SysServer simplification:

func (us *UnifiedServer) callSysServer(toolName string) (interface{}, error) {
	switch toolName {
	case "sys_init":
		return us.sysServer.SysInit()
	case "sys_list_servers":
		return us.sysServer.ListServers()
	default:
		return nil, fmt.Errorf("unknown tool: %s", toolName)
	}
}

[Copilot]

Pull request overview

This PR refactors several internal boundaries to better align responsibilities across the MCP HTTP transport layer, sys tool dispatch/session lifecycle, and tracing parent-context construction, while removing a dead SysServer routing abstraction and updating tests accordingly.

Changes:

• Inlines W3C parent span context construction into tracing.ParentContext and removes the extra forwarding layer in config_resolver.go.
• Simplifies sys tool dispatch to call SysServer.SysInit() / SysServer.ListServers() directly, and moves sys session lifecycle handlers into session.go.
• Splits HTTP transport auth/client construction helpers into a dedicated http_transport_client.go file and updates tests for the refactor.

Show a summary per file

File	Description
internal/tracing/provider.go	Inlines ParentContext W3C trace/span parsing and context enrichment.
internal/tracing/provider_test.go	Updates test descriptions to reference ParentContext after refactor.
internal/tracing/config_resolver.go	Removes the now-redundant resolveParentContext implementation.
internal/server/tool_registry.go	Switches sys tool dispatch to direct SysServer method calls and wires handlers from session.go.
internal/server/system_tools.go	Removes dead request router and exposes direct SysInit / ListServers methods.
internal/server/system_tools_test.go	Reworks tests to target direct SysInit / ListServers behavior and updates concurrency test structure.
internal/server/session.go	Adds sysInitHandler / sysListServersHandler and consolidates sys tool session lifecycle with session management.
internal/server/session_test.go	Adds coverage for the extracted sys session handlers.
internal/mcp/http_transport.go	Removes HTTP client/auth helper implementations to focus file on transport negotiation/parsing/execution.
internal/mcp/http_transport_client.go	New file containing MCP client creation + header/OIDC RoundTrippers and HTTP client construction helpers.

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• Files reviewed: 10/10 changed files
• Comments generated: 7