April 2026 (2026-04) highlights focused on stabilizing CI, expanding database tooling, and enabling reliable multi-module builds in Mill. Delivered two major features and fixed a critical CI bug, delivering tangible business value in reliability, configurability, and performance. Key outcomes: - FlywayModule: introduced flywayExtraConfig hook to allow extra Flyway properties (e.g., schemas, outOfOrder), merging into the legacy flywayInstance and propagating to all commands (flywayMigrate, flywayClean, flywayBaseline, flywayInfo, flywayDetectedDatabaseType). - ScalaPBModule: added opt-in resolveProtoc task and scalaPBProtocVersion to resolve and cache a native protoc via Coursier, reducing race conditions in parallel ScalaPB compilations; wiring through scalaPBProtocPath for end-to-end usage. - Proguard sandbox stability: fixed CI sandbox checker failures when using Coursier-managed JDKs by wrapping finalJavaHome and libraryJars in a Task context with BuildCtx.withFilesystemCheckerDisabled; added tests to validate sandbox behavior. Impact and value: - CI reliability improved due to elimination of sandbox read failures and serialized protoc resolution across parallel builds; less flaky pipelines. - Migration tooling becomes more flexible and user-friendly with per-project extra Flyway configuration, reducing boilerplate and enabling advanced migrations. - Build reliability and reproducibility improved for ScalaPB-based projects through a centralized protoc resolution approach. Commits touched (for traceability): aa6d1bf403892dedae528622a3a2d7cdad9e6a6b (Proguard sandbox fix), 21a88e4c712aa593b4ab0f62c87aed9f1d6c9ccd (Flyway extra config hook), f5bb9e2ba8cf9cb76359ab9665d22a7a73be157f (resolveProtoc task for ScalaPB).

December 2025 monthly summary for com-lihaoyi/mill: Delivered cross-language Proguard trait support enabling Java and Scala modules to share the same Proguard configuration. Implemented by replacing ScalaModule with JavaModule in the Proguard trait, preserving backward compatibility since ScalaModule extends JavaModule. This broadens support to pure Java projects and reduces integration risk for Java users, while maintaining stability for Scala projects. Work included careful refactoring and review to minimize disruption, with related PR 6473 and commit 0c9f8fe91e053b9015414edd6169fa7fe04aad79.