test: pin mask constants by re-derivation, lone-high-bit case, relative src import

[thedavidmeister]

Closes #24
Closes #25
Closes #26

Three test-suite hardening items in one file-clustered PR:

• [test-bare-src-import] [LOW] Test uses a bare src/ import (breaks when consumed as a soldeer dependency) #24: the suite imported src/lib/LibCtPop.sol bare, which breaks when the package is consumed as a soldeer dependency; it now imports relatively.
• [unpinned-masks-shared-constant-blindspot] [LOW] Mask constants have no direct test pin; ctpop/ctpopSlow share M1/M2/M4 #25: every CTPOP_M*/CTPOP_H01 constant is pinned by testMaskConstantsRederived, which rebuilds each mask with an independent loop (altMask) instead of trusting the hex literals; previously a corrupted shared constant had no direct value-level test.
• [no-single-high-bit-test] [INFO] No deterministic lone-high-bit (1<<255) test #26: testCtPopLoneHighBit deterministically pins ctpop(1 << 255) == 1 instead of relying on fuzz to reach the top bit.

Also appends the audit/mutation-test-scans.json scan record for this pass.

QA

• Discriminating tests: testMaskConstantsRederived (exact-value assertion per constant, loop-derived — not code-mirroring) and testCtPopLoneHighBit (exact count 1), both added in this PR; full suite 8/8 green on the unmutated baseline (nix develop github:rainlanguage/rainix#sol-shell -c forge test).
• Mutations applied (restore-verified after each):
  • CTPOP_M1 low nibble …55 → …54 → testMaskConstantsRederived FAILS with the exact corrupted value (deterministic kill); the fuzz/mutual-check tests also fail probabilistically because ctpop and ctpopSlow consume M1 through different formulas — the new pin makes the kill deterministic and value-level for all 9 constants, including M8–M128 which only ctpopSlow reads.
  • ctpop final shift >> 248 → >> 240 → testCtPopLoneHighBit FAILS (1 != 256), plus 4 pre-existing tests.
  • Restored → 8/8 PASS, clean tree.
• Oracle: Hamming-weight definition (the file's own Wikipedia reference) — the expected mask patterns (width set bits alternating with width clear, byte-wise 0x01 for H01) and the lone-high-bit count of 1 are derived from the definition, independent of the constants under test.
• Category check: [test-bare-src-import] [LOW] Test uses a bare src/ import (breaks when consumed as a soldeer dependency) #24 names the one bare src/ import in the repo's only test file (fixed); [unpinned-masks-shared-constant-blindspot] [LOW] Mask constants have no direct test pin; ctpop/ctpopSlow share M1/M2/M4 #25 asks for direct pins on the shared mask constants (all 9 pinned); [no-single-high-bit-test] [INFO] No deterministic lone-high-bit (1<<255) test #26 asks for the deterministic lone-high-bit case (added). Adversarial pass on the unit found no candidate bugs: the type(uint256).max special case is correct (the SWAR byte-sum overflows at count 256, which is exactly the excluded case).

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⚙️ Run configuration

Configuration used: Organization UI

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Run ID: 917394a6-9979-472c-9bee-42a2e6f87091

📥 Commits

Reviewing files that changed from the base of the PR and between 208336a and 5846438.

📒 Files selected for processing (2)

• audit/mutation-test-scans.json
• test/src/lib/LibCtPop.ctpop.t.sol

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch 2026-07-18-test-hardening

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[thedavidmeister]

🤖 ai:vetter
Reviewed 5846438: ready — closes #24 #25 #26 — relative src import, all 9 mask constants pinned by independent loop re-derivation, deterministic lone-high-bit test; assertions hand-verified, mutation claims spot-checked
cost 212 — loop-derived mask pins, verify altMask math