Reject malformed MCP environment declarations #414

🤖 Generated by the Agentic Engineer

Problem

An env array passes package validation. A client expects named string values, so the gate can mark an unusable process environment as ready.

Proposed direction

Validate optional environment maps and their string values, retaining literal variable references.

Acceptance criteria

• Reject arrays and nonstring environment values.
• Preserve empty string values and literal variable references.
• Verify the real validation result.

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