[lll-hhh]

Fixes #294.

MAP-Elites currently admits non-finite fitness into its archive. With evaluator scores [NaN, 1.0] in one cell, the real optimization loop returns best fitness NaN and acceptance history [True, False]: the finite improvement cannot replace the invalid elite. Infinite feature descriptors are also silently clipped into boundary cells.

Extend the existing numeric validation to reject non-finite fitness and descriptors with field-specific ValueErrors before archive admission or binning. NaN descriptors already fail inside integer conversion; they now receive the same clear field-specific validation error. The existing selection, mutation, finite signed fitness, and finite out-of-range descriptor clipping behavior is preserved.

Validation on Windows / Python 3.11.7:

• python -m pytest tests/src/optimizers --ignore=tests/src/optimizers/test_sew_workflow_scheme.py -q: 30 passed. The new file directly runs the actual optimizer, without model calls, network services, or mocked optimizer methods. It covers scalar/dictionary non-finite fitness, non-finite descriptors, signed finite scores, finite clipping boundaries, ties, and subsequent improvements. On unchanged main (f3d1ea5), the targeted MAP-Elites command yields 9 failed, 17 passed; patched yields 26 passed. Eight cases previously admitted invalid values; the NaN-descriptor case checks the clearer diagnostic.
• The new test file passes Ruff; git diff --check passes. The edited production file has the same 29 pre-existing Ruff diagnostics on base and patched code, with no added diagnostics; these concern existing imports/type annotations and are not reformatted in this bug fix.
• Full-suite collection was attempted on both unchanged and patched trees. Both stop at the same 15 collection errors in this local environment, including optional RAG/workflow dependencies. Thus a full-suite pass is not claimed. test_sew_workflow_scheme.py is one of those collection failures, which is why the affected optimizer group above excludes it.

Setup: isolated virtual environment with uv pip install -e '.[dev,tools,optimizers]' 'mcp<2'. The local MCP compatibility constraint is needed for FastMCP 2's McpError import with the currently resolved packages; no dependency files are changed by this PR. No GPU runs, live LLM calls, or optimization-quality gains are claimed.

This patch, issue, and verification were prepared with AI assistance. No independent human review is asserted.