[anth-volk]

Fixes #921

Same-Repository Draft PR Check

• This PR is a draft.
• This PR is from a branch in PolicyEngine/policyengine-sim-api, not a personal fork.

Summary

Last of nine stacked PRs; it builds on #946, which split the last two files over their limit. Every tracked Python file is now within the file-length limits, so this PR enforces sim.quality.python-file-length.

• Enforced: status goes from ratcheted to enforced. The baseline is empty, so rules/baselines/python-file-length.txt and the rule's [rule.baseline] table are deleted. A file over its limit now fails the quality-guards job with no way to list it.
• [rule.downgrade] removed: an enforced rule can't keep one. The section named Enforce the file-length rule and delete its empty baseline #921, which this PR's Fixes line closes when it merges.
• Tier corrected from mechanical to metric, because the rule measures a number, a file's line count, against a threshold, which is what docs/engineering/skills/rules-registry.md calls a metric rule. The proof now uses the metric fields the registry's Proof table asks for:
  • below_fixture: rules/fixtures/sim.quality.python-file-length/good_files.toml, the files at their limit (800 lines for source, 1,500 for test code), which pass;
  • above_fixture: .../bad_files.toml, the files one line over their limit, which fail;
  • threshold = 800, the source limit; both fixtures also cover the 1,500-line limit for test code, as a comment in the registry says;
  • test: the same proof test, scripts/rules/tests/test_file_length.py::TestFileLengthProof::test_rule_proof_python_file_length, run by the same job. The fixtures keep their names: the validator only requires that they exist.
• docs/engineering/skills/file-length.md replaces its baseline section with one saying there is no baseline or exception; docs/generated/rules.md is regenerated (the rule now counts as one enforced metric rule).

Environment variables

None: no workflow or deployment file changes.

Testing

• python scripts/run_quality_guards.py: every guard passed, including file-length with no baseline.
• python -m scripts.rules guard --base-ref origin/file-length-split-entry-app: passed; python -m scripts.rules render leaves no diff.
• python -m unittest discover -s scripts/rules/tests -t .: passed.
• Ruff 0.15.22 lint: clean.

Only the lowest PR in the stack runs full CI, so this PR's CI complete check fails by design until the PRs below it merge.

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