[tob-scott-a]

Changes

• Correct taint analysis for data[str(root)] = answer. Model data in answer taints data. The assignment does not taint a trusted root or the str function. Container mutations in helper functions also pass taint to the caller.
• Replace comparisons of all output path pairs with ancestor lookups. This removes quadratic work for large output lists. Keep the existing path, symlink, and overwrite checks.

Closes #22.
Closes #23.

Verification

gmake verify and all required CI checks pass.

Tests cover computed keys, helper mutations, path conflicts, and a complete compiler dry run with 10,000 output paths.