Repair the fixture evaluator and make semantic regression a CI gate

[jmcte]

Problem

The documented evaluation command currently exits 1 while the unit and scheduled CI lanes remain green:

• classification: 0/40
• semantic contract: 0/1
• noise suppression: 0/0

The evaluator and fixtures use different field/wrapper shapes, suppression reads the wrong corpus, and tests assert report shape rather than a passing, non-empty evaluation.

Relevant code

• scripts/evaluate.py:21-40,43-77,80-137
• fixtures/classification/cases.json
• fixtures/semantic/golden_outputs.json
• fixtures/noise_suppression/messages.json
• tests/test_evaluate.py
• scripts/ci/run-extended-validation.sh
• .github/workflows/extended-validation.yml:53-102

Scope

• Normalize evaluator loading to the actual fixture schemas.
• Load semantic artifacts from the top-level artifacts collection.
• Evaluate the dedicated noise-suppression corpus.
• Fail closed when an expected corpus is absent or empty.
• Assert expected case counts and overall_passed == true.
• Add per-lane counts and false-promotion/false-suppression visibility.
• Run the evaluator in extended validation.
• Include pyproject.toml, src/**, tests/**, and fixtures/** in main-push validation scope.
• Avoid rerunning a single unit test as the only “extended” behavior.

Non-goals

• Do not tune classifier rules merely to force a green result unless the fixture expectation is demonstrably wrong.
• Do not add live or private mailbox content.
• Do not make an empty evaluation pass.

Acceptance criteria

• Classification evaluates all 40 current cases with stable IDs.
• Semantic evaluation processes each artifact, not its wrapper object.
• Noise suppression evaluates a nonzero dedicated corpus.
• Missing/empty expected fixture corpora fail clearly.
• Unit tests assert exact corpus counts and overall pass state.
• Extended validation runs the evaluator and uploads or prints an inspectable summary.
• Source, test, fixture, and packaging changes cannot skip relevant post-merge validation.
• A deliberately wrong fixture expectation makes CI fail.

Validation

PYTHONDONTWRITEBYTECODE=1 PYTHONPATH=src python3.12 scripts/evaluate.py --fixtures-dir fixtures --report-json /tmp/mpi-eval.json
PYTHONDONTWRITEBYTECODE=1 PYTHONPATH=src python3.12 -m unittest tests.test_evaluate -v
bash scripts/ci/run-extended-validation.sh

Parent

Part of #98.