Back to Search-quality version diff: v1.1.0 → v1.2.0

Same caveats as `search-quality-versiondiff-v1.0.2-to-v1.2.0.md`:

- Criterion 2 (anti-hallucination). Whether an AI agent given the v1.2.0 top-K actually produces correct Swift. Phase 1.7 (`docs/design/anti-hallucination-eval.md`).
- Per-query class breakdown. The seven Phase 1.x classes (deprecation, cross-source, fragment, acronym, prose, symbol-attribute, agent-end-to-end) each have their own audit. This version diff is restricted to class A + class B.
- Coverage signals. The v1.2.0 round shipped `apple_imports_json` (1/183 → 164/183) and `swift_tools_version` (0/183 → 182/183) coverage on packages.db, but the canonical-lookup corpus doesn't query packages. Those gains land in a separate packages-side audit that doesn't exist yet.