[sunruize93-cmyk]

Fixes #110.

Summary

• Return structured request-validation errors for malformed metadata dtype and shape values instead of leaking TypeError as HTTP 500.
• Keep valid metadata serialization and the public interface unchanged; real backend errors still return HTTP 500.
• Add CPU API regressions for invalid inputs, exact field locations, and backend RuntimeError/TypeError/ValueError controls. Exception conversion is limited to the metadata validators.

Validation

Tested at b855f6f9d20bebb6d5664248164e01e7d995fe4e, based on official main 84631a24f36349435f29cc9b305aa068bed87978.

Both dependency sets used Python 3.12.13 and PyTorch 2.14.1:

FastAPI	Pydantic	HTTPX	API tests	CPU suite
0.143.2	2.14.1	0.28.1	18 passed	118 passed, 1 skipped, 12 GPU tests deselected
0.115.0	2.9.2	0.27.2	18 passed	118 passed, 1 skipped, 12 GPU tests deselected

• The same new API tests against unmodified main: 8 failed, 10 passed. The failures were HTTP 500 versus expected 422.
• Real Uvicorn/HTTPX localhost reproduction: three runs per dependency set; valid input returned 200 and all five invalid-input cases returned 422. Invalid requests did not call the backend.
• Full repository pre-commit hooks, repository-pinned Ruff 0.12.2 lint/format, targeted Pyright, compileall, and git diff whitespace checks passed.

Scope

CPU-only validation on macOS arm64. The hardware backend is stubbed, following the existing API test seam; the real application, metadata validators and HTTP transport execute. No GPU, RDMA, actual weight transfer or multi-node validation is claimed.

Kept as Draft pending my final review of the code.

[koriyoshi2041]

Validated exact head b855f6f9 on macOS arm64 with Python 3.13, FastAPI 0.159.1, Pydantic 2.14.1, and PyTorch 2.14.1. All 18 API tests pass. The malformed dtype/shape cases return 422 at the expected field location, load_metas is not called, and the backend RuntimeError/TypeError/ValueError controls still return 500. The conversion is confined to the two Pydantic validators; I did not find a broader exception-masking path in the diff.