- MockEngine popularity search uses Modrinth
downloadssort and the exact Fabric/Minecraft facets. - Reading project detail displays the author/description/license without executing remote content.
- Version selection rejects incompatible and server-only results.
- Required transitive dependency closure creates a reviewable ordered installation plan.
- Modrinth file host/filename/checksum constraints are enforced.
- Verified DownloadManager writes all requested artifacts to a staging area.
- Guarded instance import installs all JARs as one batch, rejecting name/ID collisions.
- Any failed checksum or interrupted preparation preserves installed mods and removes the staging files.
- Gradle tests/desktop compilation and native package builds succeed across supported platforms.
- Open Fabric instance → Mods → Discover on Modrinth.
- Popular list is sorted by download count and filtered for this instance's Minecraft version and loader.
- Search a known mod and inspect full project description and Modrinth page.
- Review installed file(s), version(s), optional notes and required dependency list before approving.
- Install with required dependencies, confirm files are enabled under only this instance's mods folder.
- Relaunch and verify Minecraft/Fabric loads installed mods.
- Change Minecraft version and confirm incompatible mods are no longer offered.
- Verify broken internet, 429, no matching versions, missing dependency, wrong checksum and duplicate conflicts.
- Confirm importing a local JAR still functions.
- Test resizing (400×400 up), keyboard navigation, confirmation and disabling controls while installation is busy.
- Confirm external URL opens only the official Modrinth project page.
Limitations: This is a v0.6 slice, not the complete milestone. Managed project/version persistence, compatible updates, backups and explicit last-update rollback are implemented and deterministically tested. Optional dependency choices, comprehensive version-constraint reconciliation, crash-resume recovery and native/game workflow acceptance remain open. Source project and dependencies remain under Modrinth distribution rights. User-installed mods execute third-party code when Minecraft loads.
Optional branches can be selected in advanced review; unselected branches are not fetched. Tests cover required closure of selected branches, deselection, same-plan conflicts, enabled managed-origin conflicts before download and a locked publication recheck. EN/PL/DE compact UI tests prevent installation during replanning. API 429/transient retry is bounded to three attempts with capped Retry-After. Full arbitrary installed-mod/version-range reconciliation and native gameplay acceptance remain open. See C06.