Collapse duplicate unregistered custom-type handling in config validation

[Copilot]

validateCustomServerConfig had two adjacent branches that produced the same rules.UnsupportedType(...) error for the same condition in practice: the custom type was not present in customSchemas. This change removes that duplication and keeps the unsupported custom-type error path defined in one place.

• Validation flow

  • Remove the explicit customSchemas == nil early return from validateCustomServerConfig
  • Rely on Go's nil-map lookup semantics so both nil and missing-key cases fall through the same !exists branch

• Behavior

  • Preserve the existing user-facing error for unregistered custom server types
  • Keep nil and missing-entry handling equivalent, but without duplicating the error construction

• Coverage

  • Existing tests for both nil customSchemas and unregistered custom types continue to exercise the shared path

schemaValue, exists := customSchemas[serverType]
if !exists {
	return rules.UnsupportedType(
		"type",
		serverType,
		jsonPath,
		"Custom server type '"+serverType+"' is not registered in customSchemas. "+
			"Add the custom type to the customSchemas field or use a standard type ('stdio' or 'http')",
	)
}

[Copilot]

Pull request overview

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This PR simplifies validateCustomServerConfig by removing duplicate logic for handling unregistered custom server types, relying on Go’s nil-map lookup behavior to unify the error path.

Changes:

• Removed the explicit customSchemas == nil early return branch.
• Consolidated nil map and missing-key handling into the existing !exists branch.

Show a summary per file

File	Description
internal/config/validation.go	Removes duplicate nil-check branch so unregistered custom types share one error path

Copilot's findings

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• Files reviewed: 1/1 changed files
• Comments generated: 1

[lpcox]

@copilot address review feedback

[Copilot]

@copilot address review feedback

Addressed in c4c35c9. I kept the unified unsupported-type error path and restored the nil-vs-missing distinction in logging by appending a (no customSchemas) suffix only when customSchemas is nil.