Expand backend API contract edge-case tests

[felixvippp-ai]

Summary

Closes #1

Expands backend API contract edge-case coverage and makes the offline mock client return structured validation errors for missing request bodies, missing required fields, and malformed field types.

Changes

• Added schema-aware request payload validation for required fields and JSON Schema primitive types.
• Added deterministic negative tests for missing required fields and malformed field types.
• Added async negative-path coverage with asyncio.run, so the suite does not require optional pytest async plugins.
• Documented the focused local test command in tests/backend_api/README.md.
• Committed diagnostic/build-011bb3d4.json, generated by build.py after the repo encryptly preflight failed on this Windows environment.

Testing

• .\.venv\Scripts\python.exe -m pytest -q tests\backend_api -> 15 passed.
• .\.venv\Scripts\python.exe -m py_compile backend\api_contract.py tests\conftest.py tests\backend_api\test_openapi_contract.py -> passed.
• python build.py -> failed during encryptly preflight before module builds; it generated diagnostic/build-011bb3d4.json explaining why no encrypted .logd was created.

Checklist

• Relevant modules affected by these changes build locally
• Tests pass locally
• Diagnostic build log is committed in this PR
• Documentation has been updated, if applicable
• Configuration or schema changes are documented, if applicable
• No generated build artifacts are committed, except the required diagnostic build log
• Changes are scoped to the PR purpose and avoid unrelated cleanup
• Security, privacy, and error-handling implications have been considered

---

• I would like to request that my diagnostic build log is removed before merging

Bounty payout address: 0x1aba67a6f349826fbaea17f54556a42d42399474

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 954ee3b8-254e-415a-86f1-22a1ef8b2cb8

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[felixvippp-ai]

Status refresh for review:

This PR is still current for bounty issue #1 and remains ready for review. The focused backend API contract suite passed locally (15 passed), and the PR body includes the Windows build.py diagnostic JSON explaining why the encrypted .logd artifact could not be produced in this environment.

Please let me know if any final change is needed before acceptance or bounty payment review.

Payment address: 0x1aba67a6f349826fbaea17f54556a42d42399474