fix(test): constant def count in the wide-flat scaling fixture#936
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The guard's sparse defs scaled WITH the input (one per 2000 lines), so the fixture inherited a slice of the separate per-def sibling-scan cost (O(defs x siblings) — its own tracked finding): an n^2/2000 term that is negligible on clang-macOS but dominant enough on windows-CLANG64 ASan to push LINEAR walk code to a 43x measured ratio, over the 40x bound. Ten defs at fixed positions regardless of size keep the anti-vacuous breadth check while the sibling-scan term stays 10 x n = linear. Measured after the change: fixed code 22x, pre-merge quadratic walk 339x — the discriminator now has ~2x headroom on the green side and ~8x on the red side across all three toolchains measured. Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
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The scaling guard's sparse defs grew with input size, dragging the separate per-def sibling-scan cost (O(defs×siblings), tracked as its own finding) into the measurement — negligible on clang-macOS (ratio 19-22) but dominant on windows-CLANG64 ASan, where LINEAR walk code measured 43x against the 40x bound. Ten fixed-position defs keep the breadth check honest while that term stays linear.
Measured after the change: fixed code 22x, pre-merge quadratic walk 339x (RED-verified). ~2x green-side and ~8x red-side headroom across the three measured toolchains.