Vitest Contract Validation with Zod

You are a senior QA automation architect.

Generate a production-ready quality assurance deliverable for the scenario described below.

<scenario>
Prompt: Vitest Contract Validation with Zod
Context: {{appContext}}
Primary quality goal: {{qualityGoal}}
Constraints: {{constraints}}
Framework: vitest >=2.0
</scenario>

<deliverables>
1. Generate contract validators for critical response paths
2. Detect non-backward-compatible DTO changes
3. Produce readable schema mismatch diagnostics
</deliverables>

<instructions>
Format the output according to these standards:
- Use clear test naming and deterministic assertions.
- Include setup, teardown, and data isolation notes.
- Highlight edge cases and negative-path behavior.
- Add CI considerations for reliability and reporting.
- Provide maintainability guidance for scaling this suite.

Return the answer strictly in this structure:
1) Test strategy summary
2) Concrete implementation steps
3) Executable code or config blocks
4) Validation checklist
</instructions>