Validate MCP transport selectors and executable values #412

🤖 Generated by the Agentic Engineer

Problem

The package gate accepts a numeric command as an executable. The same boundary does not establish a usable transport before declaring a bundled connection valid.

Proposed direction

Validate transport declarations and nonblank command or endpoint strings with coherent transport selection.

Acceptance criteria

• Reject nonstring or blank commands and endpoints and contradictory transport declarations.
• Preserve valid local and declared remote transports.
• Observe rejection through the real package gate.

Reproduced on current main before implementation. Rough size: S.