Forward MCP streamable HTTP headers

[jstar0]

Fixes #295

Summary

Forwards custom MCP server HTTP headers from the top-level headers field into requestInit.headers.

Changes

This PR:

• copies each MCP server's top-level headers into requestInit.headers
• keeps the original top-level headers field intact
• preserves any existing requestInit.headers value when the same header is already set there
• supports both VS Code-style { "servers": ... } config and direct server-map config
• skips malformed non-object requestInit or requestInit.headers shapes instead of replacing user-provided values
• adds regression coverage for the wrapped config, direct config, and duplicate-header precedence cases

Why

Streamable HTTP MCP servers may require custom HTTP headers for authentication. The settings adapter already forwards MCP server configuration to the language server, but top-level headers were not represented in requestInit.headers, so those headers were not available to the Streamable HTTP request path.

Verification

./mvnw -pl com.microsoft.copilot.eclipse.core,com.microsoft.copilot.eclipse.core.test -am -Dtest=CopilotLanguageServerSettingsTests verify

[Copilot]

Pull request overview

This PR fixes MCP Streamable HTTP authentication gaps by ensuring any top-level per-server headers in the MCP JSON config are forwarded into requestInit.headers (without removing the original headers field), so the Streamable HTTP request path can include them.

Changes:

• Normalize MCP server configs by copying server.headers into server.requestInit.headers when not already present there (preserving requestInit.headers precedence).
• Support both VS Code-style wrapped configs ({ "servers": { ... } }) and direct server-map configs ({ "my-server": { ... } }).
• Add regression tests covering wrapped config, direct config, and duplicate-header precedence.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
com.microsoft.copilot.eclipse.core/src/com/microsoft/copilot/eclipse/core/lsp/protocol/CopilotLanguageServerSettings.java	Parses MCP server JSON as JsonObject and normalizes headers into requestInit.headers while preserving existing values and skipping malformed shapes.
com.microsoft.copilot.eclipse.core.test/src/com/microsoft/copilot/eclipse/core/lsp/protocol/CopilotLanguageServerSettingsTests.java	Adds unit tests verifying header forwarding for wrapped/direct configs and that requestInit.headers takes precedence on duplicates.