Add CI test for MCP server compile tool error handling

[Copilot]

Adds CI validation that the gh-aw MCP server correctly exposes the compile tool and returns errors for invalid workflows.

Changes

• New CI job mcp-server-compile-test that:
  • Spawns MCP server via Go SDK's stdio transport
  • Invokes compile tool through MCP protocol
  • Validates error response structure (valid: false, errors array)
  • Tests with workflow containing invalid frontmatter field

Implementation

// Connects to MCP server and calls compile tool
client := mcp.NewClient(&mcp.Implementation{
    Name: "ci-test-client", Version: "1.0.0",
}, nil)

serverCmd := exec.Command(binaryPath, "mcp-server", "--cmd", binaryPath)
session, _ := client.Connect(ctx, &mcp.CommandTransport{Command: serverCmd}, nil)

// Invoke compile on invalid workflow
result, err := session.CallTool(ctx, &mcp.CallToolParams{
    Name: "compile",
    Arguments: map[string]any{"workflows": []string{"test-invalid.md"}},
})

The test verifies end-to-end MCP server functionality: tool discovery, invocation, and error propagation for validation failures.

Original prompt

Add new ci.yml job that runs a compile command through the gh-aw MCP server.

• builds gh-aw
• launches the gh-aw mcp-server
• uses the inspect command to invoke the "compile" tool and retrieve the output

The tool should emit an error.

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