Add test coverage for HTTP MCP server URL validation

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The schema already validates that HTTP MCP servers require a url field via the http_mcp_tool definition in main_workflow_schema.json. This validation provides early feedback during workflow parsing, before runtime execution.

Changes

• Test coverage: Added TestHTTPMCPServerRequiresURL to verify and document the existing validation behavior across three scenarios:
  • HTTP MCP server with type: http but missing url (validation fails)
  • HTTP MCP server with explicit type and url (validation passes)
  • HTTP MCP server with url only, no explicit type (validation passes via type inference)

Example

# ❌ Fails validation
mcp-servers:
  api:
    type: http
    # missing url field

# ✓ Passes validation  
mcp-servers:
  api:
    type: http
    url: "https://api.example.com"

Error message when url is missing:

error: at '/mcp-servers/api': missing property 'url'

The validation is enforced by the JSON schema during workflow compilation, providing IDE/editor feedback without requiring runtime checks.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[task] Add required 'url' field to HTTP MCP tool schema</issue_title>
<issue_description>## Objective
Make the url field required in the MCP config schema for HTTP MCP tools to provide early validation feedback.

Context

This addresses Issue #2 from discussion #2969. Currently, the MCP config schema doesn't enforce the url field as required via JSON Schema, but the compiler enforces it at runtime in pkg/workflow/mcp-config.go:827. Users don't get IDE validation or early warning when url is missing.

Approach

1. Open pkg/parser/schemas/mcp_config_schema.json
2. Locate the http_mcp_tool definition
3. Add a conditional required array that enforces url when type is http
4. Follow the existing pattern used in MCP schemas (which are noted as "gold standard")

Files to Modify

• pkg/parser/schemas/mcp_config_schema.json - Add conditional requirement for url field in HTTP tools

Acceptance Criteria

• Schema validation fails when HTTP MCP tool lacks url field
• Schema validation passes when url is provided for HTTP tools
• Non-HTTP MCP tools are unaffected
• IDE validation provides early feedback
• Run make build and make test successfully
  Related to [Schema Consistency] 🔍 Schema Consistency Check - Required Fields & Error Documentation Gap (Nov 2, 2025) #2969

AI generated by Plan Command for discussion #2969</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [task] Add required 'url' field to HTTP MCP tool schema #2972

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Pull Request Overview

This PR adds validation testing for HTTP MCP server configurations to ensure they require a URL field. The test verifies that HTTP MCP servers fail validation when missing a URL, pass when URL is present with explicit type, and pass when URL is present with inferred type.

• Validates that HTTP MCP servers without a URL field fail compilation
• Confirms HTTP MCP servers with URL field compile successfully
• Tests type inference when URL is present without explicit type

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